Influence of urate-lowering therapies on renal handling of uric acid

Association between urinary uric acid excretion and kidney outcome in patients with CKD

Inhibiting tubular urate reabsorption may protect the kidney from urate-induced tubular injury. However, this approach may promote intratubular uric acid crystallization, especially in acidified urine, which could be toxic to the kidney. To assess how tubular urate handling affects kidney outcomes, we conducted a retrospective cohort study including 1042 patients with estimated glomerular filtration rates (eGFR) of 15-60 mL/min/1.73 m2. The exposures were fractional excretion of uric acid (FEUA) and urinary uric acid-to-creatinine ratio (UUCR). The kidney outcome was defined as a halving of eGFR from baseline or initiating kidney replacement therapy. The median FEUA and UUCR were 7.2% and 0.33 g/gCre, respectively. During a median follow-up of 1.9 years, 314 kidney outcomes occurred. In a multivariate Cox model, the lowest FEUA quartile exhibited a 1.68-fold higher rate of kidney outcome than the highest FEUA quartile (95% confidence interval, 1.13-2.50; P = 0.01). Similarly, lower UUCR was associated with a higher rate of kidney outcome. Notably, patients in the highest quartile of FEUA and UUCR were at the lowest risk of kidney outcome even among those with aciduria. In conclusion, lower FEUA and UUCR were associated with a higher risk of kidney failure, suggesting that increased urate reabsorption is harmful to the kidney.

A highly sensitive dual-read assay using nitrogen-doped carbon dots for the quantitation of uric acid in human serum and urine samples

A simple dual-read assay for uric acid (UA) was developed based on a combined ratiometric fluorescent and colorimetric strategy using nitrogen-doped carbon dots (N-CDs). The biosensor relies on the oxidation of UA by uricase to produce H2O2, which was then converted to •OH radicals by I-, resulting in the oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP). In the presence of UA, the colorless biosensor system changed to yellow. Furthermore, the presence of DAP quenched the fluorescence emission of the N-CDs at 427 nm based on the inner filter effect (IFE). With increasing UA concentrations, the fluorescence intensity of the biosensor at 427 nm decreased but increased at 580 nm, demonstrating the ratiometric response. A strong linearity was observed between the fluorescence intensity ratio of DAP to N-CDs (I580/I427) and the corresponding UA concentration over the range 0.5-150 μM, and a limit of detection (S/N ratio of 3) of 0.06 μM was calculated. The dual-read assay was successfully employed in the quantitation of UA in human serum and urine samples, revealing its potential for measuring UA in clinical samples.

Efficacy of different urinary uric acid indicators in patients with chronic kidney disease

Background

Mounting studies have shown that hyperuricemia is related to kidney diseases through multiple ways. However, the application of urinary uric acid indicators in patients with reduced renal function is not clear. In this study, we aim to determine the effects of renal function on various indicators reflecting uric acid levels in patients with chronic kidney disease (CKD).

Methods

Anthropometric and biochemical examinations were performed in 625 patients with CKD recruited from Dept of Nephrology of Huadong hospital affiliated to Fudan University. Multiple regression analyses were used to study correlations of the estimated glomerular filtration rate (eGFR) with serum uric acid (SUA) and renal handling of uric acid. For further study, smooth curve plots and threshold effect analyses were applied to clarify associations between renal function and uric acid levels.

Results

The nonlinear relationships were observed between eGFR and urinary uric acid indicators. The obvious inflection points were observed in smooth curve fitting of eGFR and fractional excretion of uric acid (FEur), excretion of uric acid per volume of glomerular filtration (EurGF). In subsequent analyses where levels of eGFR< 15 mL/min/1.73m² were dichotomized (CKD5a/CKD5b), patients in the CKD5a showed higher levels of FEur and EurGF while lower levels of urinary uric acid excretion (UUA), clearance of uric acid (Cur) and glomerular filtration load of uric acid (FLur) compared with CKD5b group (all P < 0.05). And there was no significant difference of SUA levels between two groups. On the other hand, when eGFR< 109.9 ml/min/1.73 m² and 89.1 ml/min/1.73 m², the resultant curves exhibited approximately linear associations of eGFR with Cur and FLur respectively.

Conclusion

FEur and EurGF showed significantly compensatory increases with decreased renal function. And extra-renal uric acid excretion may play a compensatory role in patients with severe renal impairment to maintain SUA levels. Moreover, Cur and FLur may be more reliable indicators of classification for hyperuricemia in CKD patients.

The Role of a “Treat-to-Target” Approach in the Long-Term Renal Outcomes of Patients with Gout

Background: Although gout is accompanied by the substantial burden of kidney disease, there are limited data to assess renal function as a therapeutic target. This study evaluated the importance of implementing a “treat-to-target” approach in relation to renal outcomes. Methods: Patients with gout who underwent continuous urate-lowering therapy (ULT) for at least 12 months were included. The effect of ULT on renal function was investigated by means of a sequential comparison of the estimated glomerular filtration rate (eGFR). Results: Improvement in renal function was only demonstrated in subjects in whom the serum urate target of <6 mg/dL was achieved (76.40 ± 18.81 mL/min/1.73 m2 vs. 80.30 ± 20.41 mL/min/1.73 m2, p < 0.001). A significant difference in the mean change in eGFR with respect to serum urate target achievement was shown in individuals with chronic kidney disease stage 3 (−0.35 ± 3.87 mL/min/1.73 m2 vs. 5.33 ± 11.64 mL/min/1.73 m2, p = 0.019). Multivariable analysis predicted that patients ≥65 years old had a decreased likelihood of improvement (OR 0.31, 95% CI 0.13–0.75, p = 0.009). Conclusions: The “treat-to-target” approach in the long-term management of gout is associated with better renal outcomes, with a greater impact on those with impaired renal function.

Evaluation of the chemical composition of nephrolithiasis using dual-energy CT in Southern Chinese gout patients

Background

A study to evaluate the prevalence of uric acid (UA) nephrolithiasis with dual-energy CT (DECT) and explore the risk factors for kidney stones in primary gout patients.

Methods

Eighty-four consecutive gout patients underwent urinary tract ultrasonography or DECT to confirm the existence of kidney stones. Urine and blood samples were also taken for laboratory analysis.

Results

Forty-one subjects (48.8%) had nephrolithiasis diagnosed; 38 had a kidney stone. Thirty-two of the 38 patients underwent a DECT scan, and 27 patients had nephrolithiasis in DECT. Among them, 63.0% (17/27) and 14.8% (4/21) of the patients had pure UA and UA-based mixed stone, respectively, and 22.2% (6/27) had a non-UA stone. Those with nephrolithiasis suffered from more frequent acute attacks and had longer disease durations of gout. At least one urine biochemical abnormality was found in 81% of patients. Forty-four (55.0%) patients presented hypomagnesuria. Forty-three (51.8%) patients had low urine volume. Unduly acidic urine (UAU) was present in 36 patients (44.4%). Hyperuricosuria was only found in ten (12.2%) patients. In comparison to the non-lithiasic group, the lithiasic group was more likely to have a UAU. Binary logistic regression showed that female gender was a protective factor, while disease duration of gout and low urine pH were risk factors for nephrolithiasis.

Conclusion

Our results indicated that nephrolithiasis, especially UA stones, were more common than previous reports in gout patients indicated, and that disease duration of gout, and low urine pH, were risk factors for nephrolithiasis.

Highly Acylated Anthocyanins from Purple Sweet Potato ( Ipomoea batatas L.) Alleviate Hyperuricemia and Kidney Inflammation in Hyperuricemic Mice: Possible Attenuation Effects on Allopurinol

Allopurinol is the first-line medication for hyperuricemia treatment. However, severe drug-related adverse effects have often been reported among patients who received allopurinol administration. This study is aimed at evaluating the possible attenuation effects of highly acylated anthocyanins from purple sweet potato (HAA-PSP) on hyperuricemia and kidney inflammation in hyperuricemic mice treated with allopurinol. In comparison with 5 mg kg^-1 allopurinol used alone, the combination of 25 mg kg^-1 HAA-PSP and 2.5 mg kg^-1 allopurinol could not only reduce serum uric acid level in hyperuricemic mice but also attenuate the kidney damage, as indicated by the level of serum biomarkers as well as histopathological examination. The inflammatory response was partially mitigated by inhibiting the protein expression of typical cytokines in the kidney. Our findings provide new evidence for the supplementary therapeutic potential of HAA-PSP with allopurinol on hyperuricemia and inflammation-related syndromes. Moreover, this study provides a theoretical basis for assessing the potential of anthocyanin-rich foods in health.

Renal excretion is a cause of decreased serum uric acid during acute gout

AIMS

To evaluate the fluctuation of serum uric acid (SUA) during acute gout (AG) and explore its potential mechanisms.

METHODS

Data such as SUA, urinary uric acid and 24-hour uric acid urinary excretion were collected from 126 patients diagnosed with gout and were analyzed.

RESULTS

Serum uric acid was negatively correlated with age in gout patients, and significantly elevated in patients aged ≤50 years. Twenty-four-hour uric acid urinary excretion was affected by SUA, creatinine clearance, age, body mass index and urine volume. In contrast, clearance of uric acid and fractional excretion of uric acid (FEur) were more stable. SUA was significantly downregulated during acute attacks. Of the AG patients, 34.92% had detected SUA <420 μmol/L. Clearance of uric acid and FEur were notably increased in patients during acute attacks, especially in patients with SUA <420 μmol/L.

CONCLUSION

This study demonstrated that the level of SUA was remarkably upregulated in young gout patients. Therefore, early onset of gout should be considered of great importance. SUA was downregulated during acute gouty arthritis, which might be associated with increased urinary excretion of uric acid.

Association of Chronic Kidney Disease With Allopurinol Use in Gout Treatment

IMPORTANCE

Clinicians are often cautious about use of allopurinol in patients with gout when renal function declines.

OBJECTIVE

To assess the association of allopurinol use in gout with the risk of developing chronic kidney disease stage 3 or higher.

DESIGN, SETTING, AND PARTICIPANTS

A time-stratified propensity score-matched, population-based, prospective cohort study of individuals with newly diagnosed gout who initiated allopurinol (≥300 mg/d) compared with those who did not initiate allopurinol, using the Health Improvement Network (THIN), a United Kingdom general practitioner electronic health records database, was carried out. The data were analyzed using Cox proportional hazards regression. Among adults aged 18 to 89 years with newly diagnosed gout, we propensity score matched 4760 initiators of allopurinol (≥300 mg/d) to the same number of noninitiators of allopurinol, excluding those with chronic kidney disease stage 3 or higher or urate-lowering therapy use before their gout diagnosis.

EXPOSURES

Allopurinol initiation at a dose of 300 mg or more per day.

MAIN OUTCOMES AND MEASURES

Development of chronic kidney disease stage 3 or higher.

RESULTS

Of the 4760 allopurinol initiators (3975 men, 785 women) and same number of noninitiators (3971 men, 789 women), 579 and 623, respectively, developed chronic kidney disease stage 3 or higher, with a mean follow-up time of 5 and 4 years, mean age of 57 years, and mean body mass index (calculated as weight in kilograms divided by height in meters squared) of 30 for both groups. Use of allopurinol of at least 300 mg/d was associated with lower risk of developing chronic kidney disease stage 3 or higher compared with nonusers, with a hazard ratio (HR) of 0.87 (95% CI, 0.77-0.97). Allopurinol initiation at less than 300 mg/d was not associated with renal function decline (HR, 1.00; 95% CI, 0.91-1.09).

CONCLUSIONS AND RELEVANCE

In this large cohort, allopurinol initiation of at least 300 mg/d was associated with a lower risk of renal function deterioration. Because allopurinol does not appear to be associated with renal function decline, clinicians should consider evaluating other potential causes when patients with gout experience renal function decline.

The urate-lowering efficacy and safety of febuxostat versus allopurinol in Chinese patients with asymptomatic hyperuricemia and with chronic kidney disease stages 3-5

BACKGROUND

While the dose of allopurinol is limited in patients with chronic kidney disease (CKD), information is lacking concerning the efficacy, safety, and maintenance dose of febuxostat in Chinese patients with hyperuricemia and with CKD stages 3-5.

METHODS

A single center, prospective cohort study was conducted in patients with CKD stages 3-5 and with hyperuricemia who had not yet begun to undergo renal replacement therapy. We enrolled 208 patients who were newly treated with febuxostat (n = 112) or allopurinol (n = 96) in this study. The efficacy of febuxostat was determined by the proportion of patients with serum uric acid (sUA) < 360 µmol/L at the end of the study and changes of renal function.

RESULTS

The target of sUA < 360 µmol/L was reached by 96.4% of participants in the febuxostat group and 37.5% in the allopurinol group at 6 months. The eGFR in the febuxostat group showed an increase from 28.45 to 30.65 mL/min/1.73 m² at 6 months, while in the allopurinol group, the eGFR decreased from 28.06 to 24.39 mL/min/1.73 m². Linear regression analysis showed that the reduction in sUA was significantly associated with an increase in eGFR and decrease in proteinuria. We found that 83.0% of the patients could remain with sUA < 360 µmol/L at a maintenance dose of febuxostat 20 mg/day.

CONCLUSION

Febuxostat had superior urate-lowering efficacy to that of allopurinol in Chinese Han patients with hyperuricemia with CKD stages 3-5, and the reduction in sUA levels was associated with a slower progression of renal function.

Physiology of Hyperuricemia and Urate-Lowering Treatments

Gout is the most common form of inflammatory arthritis and is a multifactorial disease typically characterized by hyperuricemia and monosodium urate crystal deposition predominantly in, but not limited to, the joints and the urinary tract. The prevalence of gout and hyperuricemia has increased in developed countries over the past two decades and research into the area has become progressively more active. We review the current field of knowledge with emphasis on active areas of hyperuricemia research including the underlying physiology, genetics and epidemiology, with a focus on studies which suggest association of hyperuricemia with common comorbidities including cardiovascular disease, renal insufficiency, metabolic syndrome and diabetes. Finally, we discuss current therapies and emerging drug discovery efforts aimed at delivering an optimized clinical treatment strategy.

Urinary excretion of uric acid is negatively associated with albuminuria in patients with chronic kidney disease: a cross-sectional study

Background

Increasing evidence has shown that albuminuria is related to serum uric acid. Little is known about whether this association may be interrelated via renal handling of uric acid. Therefore, we aim to study urinary uric acid excretion and its association with albuminuria in patients with chronic kidney disease (CKD).

Methods

A cross-sectional study of 200 Chinese CKD patients recruited from department of nephrology of Huadong hospital was conducted. Levels of 24 h urinary excretion of uric acid (24-h Uur), fractional excretion of uric acid (FEur) and uric acid clearance rate (Cur) according to gender, CKD stages, hypertension and albuminuria status were compared by a multivariate analysis. Pearson and Spearman correlation and multiple regression analyses were used to study the correlation of 24-h Uur, FEur and Cur with urinary albumin to creatinine ratio (UACR).

Results

The multivariate analysis showed that 24-h Uur and Cur were lower and FEur was higher in the hypertension group, stage 3–5 CKD and macro-albuminuria group (UACR> 30 mg/mmol) than those in the normotensive group, stage 1 CKD group and the normo-albuminuria group (UACR< 3 mg/mmol) (all P < 0.05). Moreover, males had higher 24-h Uur and lower FEur than females (both P < 0.05). Multiple linear regression analysis showed that UACR was negatively associated with 24-h Uur and Cur (P = 0.021, P = 0.007, respectively), but not with FEur (P = 0.759), after adjusting for multiple confounding factors.

Conclusions

Our findings suggested that urinary excretion of uric acid is negatively associated with albuminuria in patients with CKD. This phenomenon may help to explain the association between albuminuria and serum uric acid.

The Dietary Fructose:Vitamin C Intake Ratio Is Associated with Hyperuricemia in African-American Adults

Background

A high fructose intake has been shown to be associated with increased serum urate concentration, whereas ascorbate (vitamin C) may lower serum urate by competing with urate for renal reabsorption.

Objective

We assessed the combined association, as the fructose:vitamin C intake ratio, and the separate associations of dietary fructose and vitamin C intakes on prevalent hyperuricemia.

Methods

We conducted cross-sectional analyses of dietary intakes of fructose and vitamin C and serum urate concentrations among Jackson Heart Study participants, a cohort of African Americans in Jackson, Mississippi, aged 21-91 y. In the analytic sample (n = 4576), multivariable logistic regression was used to examine the separate associations of dietary intakes of fructose and vitamin C and the fructose:vitamin C intake ratio with prevalent hyperuricemia (serum urate ≥7 mg/dL), after adjusting for age, sex, smoking, waist circumference, systolic blood pressure, estimated glomerular filtration rate, diuretic medication use, vitamin C supplement use, total energy intake, alcohol consumption, and dietary intake of animal protein. Analyses for individual dietary factors (vitamin C, fructose) were adjusted for the other dietary factor.

Results

In the fully adjusted model, there were 17% greater odds of hyperuricemia associated with a doubling of the fructose:vitamin C intake ratio (OR: 1.17; 95% CI: 1.08, 1.28), 20% greater odds associated with a doubling of fructose intake (OR: 1.20; 95% CI: 1.08, 1.34), and 13% lower odds associated with a doubling of vitamin C intake (OR: 0.87; 95% CI: 0.78, 0.97). Dietary fructose and the fructose:vitamin C intake ratio were more strongly associated with hyperuricemia among men than women (P-interaction ≤ 0.04).

Conclusion

Dietary intakes of fructose and vitamin C are associated with prevalent hyperuricemia in a community-based population of African Americans.

The prevalence, subtypes and associated factors of hyperuricemia in lupus nephritis patients at chronic kidney disease stages 1-3

There is a high prevalence of hyperuricemia (HUA) in the chronic kidney disease (CKD) population. However, there's a dearth of research on HUA's prevalence, subtypes, early detection, and treatment strategies of HUA in lupus nephritis (LN) patients. The aim of this study is to address these knowledge gaps. LN patients presenting to the Department of Nephrology at Shanghai Rui Jin Hospital from January 2011 to January 2016 were recruited. The effective sample size was derived using the power analysis. The demographic, clinical and laboratory characteristics of the LN patients with HUA were compared with those of patients without HUA. Two statistical models for analyzing HUA were built and compared using the receiver operating characteristic (ROC) curve analysis. The total prevalence of HUA in the cohort was 40.11%. The subtypes of HUA included urate underexcretion-type, overproduction-type and combined-type, which proportion being 67.7%, 9.7% and 22.6% respectively. The CKD stage was closely associated with the prevalence of HUA in patients with LN. The other significant associated factors were hypertension, triglycerides, serum creatinine, serum albumin, hemoglobin, parathyroid hormone, phosphorus, calcium, etc. The statistical algorithm successfully identified LN patients at risk of HUA. In conclusion, there was a high prevalence of HUA in LN patients at CKD stages 1-3, and renal underexcretion hyperuricemia was the most prevalent subtype. The occurrence of HUA in LN may be related to renal insufficiency, metabolic disorder and lupus itself. Early care coordination programs can employ risk models to improve HUA prevention and target interventions in LN patients.

Management of Gout and Hyperuricemia in CKD

Hyperuricemia and gout, the clinical manifestation of monosodium urate crystal deposition, are common in patients with chronic kidney disease (CKD). Although the presence of CKD poses additional challenges in gout management, effective urate lowering is possible for most patients with CKD. Initial doses of urate-lowering therapy are lower than in the non-CKD population, whereas incremental dose escalation is guided by regular monitoring of serum urate levels to reach the target level of <6mg/dL (or <5mg/dL for patients with tophi). Management of gout flares with presently available agents can be more challenging due to potential nephrotoxicity and/or contraindications in the setting of other common comorbid conditions. At present, asymptomatic hyperuricemia is not an indication for urate-lowering therapy, though emerging data may support a potential renoprotective effect.

Clinical, Genetic, and Urinary Factors Associated with Uromodulin Excretion

BACKGROUND AND OBJECTIVES

The urinary excretion of uromodulin is influenced by common variants in the UMOD gene, and it may be related to NaCl retention and hypertension. Levels of uromodulin are also dependent of the renal function, but other determinants remain unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We tested associations between the urinary excretion of uromodulin; medical history and medication; serum and urinary levels of electrolytes, glucose, and uric acid; and the genotype at the UMOD/Protein Disulfide Isomerase-Like, Testis Expressed locus (rs4293393 and rs12446492); 943 participants from the CARTaGENE Cohort, a random sample from the Canadian population of 20,004 individuals, were analyzed. Participants with available genotyping were obtained from a substudy addressing associations between common variants and cardiovascular disease in paired participants with high and low Framingham risk scores and vascular rigidity indexes.

RESULTS

The population studied was 54±9 years old, with 51% women and eGFR of 9±14 ml/min per 1.73 m(2). Uromodulin excretion was 25 (11-42) mg/g creatinine. Using linear regression, it was independently higher among patients with higher eGFR, the TT genotype of rs4293393, and the TT genotype of rs12446492. The fractional excretions of urate and sodium showed a strong positive correlation with uromodulin, likely linked to the extracellular volume status. The presence of glycosuria and the use of uricosuric drugs, which both increased the fraction excretion of urate, were independently associated with a lower uromodulin excretion, suggesting novel interactions between uric acid and uromodulin excretion.

CONCLUSIONS

In this large cohort, the excretion of uromodulin correlates with clinical, genetic, and urinary factors. The strongest associations were between uric acid, sodium, and uromodulin excretions and are likely linked to the extracellular volume status.