Renal impairment and gout

Association of acidic urine pH with impaired renal function in primary gout patients: a Chinese population-based cross-sectional study

Background

Patients with gout frequently have low urinary pH, which is associated with the nephrolithiasis. However, the specific distribution of urinary pH and potential relationship of acidic urine pH to broader manifestations of kidney disease in gout are still poorly understood.

Methods

A 2016–2020 population-based cross-sectional study was conducted among 3565 gout patients in the dedicated gout clinic of the Affiliated Hospital of Qingdao University to investigate the association between low urinary pH and kidney disease. We studied patients that we defined to have “primary gout”, based on the absence of > stage 2 CKD. All subjects underwent 14 days of medication washout and 3-day standardized metabolic diet. We obtained general medical information, blood and urine biochemistries, and renal ultrasound examination on the day of the visit. The primary readouts were urine pH, eGFR, nephrolithiasis, renal cysts, microhematuria, and proteinuria. Patients were assigned into 5 subgroups (urine pH ≤5.0, 5.0 <pH≤ 5.5, 5.5 <pH< 6.2, 6.2 ≤pH≤ 6.9, and pH >6.9), aligning with the clinical significance of urine pH.

Results

Overall, the median urine pH and eGFR of all patients was 5.63 (IQR 5.37~6.09), and 98.32 (IQR 86.03~110.6), with acidic urine in 46.5% of patients. The prevalence of nephrolithiasis, microhematuria, and proteinuria were 16.9%, 49.5%, and 6.9%, respectively. By univariate analysis, eGFR was significantly associated with age, sex, duration of gout, tophus, body mass index, systolic blood pressure, diastolic blood pressure, fasting blood glucose, total cholesterol, serum utare, hypertension, diabetes, and urine pH. On multivariable analysis, eGFR was associated with age, sex, diastolic blood pressure, serum uric acid, hypertension, diabetes, and urine pH. Acidic urine pH, especially urine pH < 5.0, was significantly associated with the prevalence of kidney disease, including > stage 1 CKD, nephrolithiasis, kidney cyst, and microhematuria. Patients with 6.2 ≤ urine pH ≤ 6.9 and SU ≤ 480 μmol/L had the highest eGFR with the lowest prevalence of nephrolithiasis, microhematuria, and proteinuria.

Conclusions

Approximately half of gout subjects had acidic urine pH. Urine pH < 5.0 was associated with significantly increased nephrolithiasis, renal cyst, microhematuria, and proteinuria. The results support prospective clinical investigation of urinary alkalinization in selected gout patients with acidic urine pH.

Age-Specific Imbalance of Circulating Tfh Cell Subsets and Its Association With Gout-Targeted Kidney Impairment

Objective

Gout is a chronic disease characterized by the deposition of monosodium urate (MSU) crystals in tissue. Study with a focus on adaptive immune response remains to be understood although innate immune response has been reported extensively in gout etiology. Our study attempted to investigate the association of gout-related immune cell imbalance with clinical features and comorbidity with renal impairment and the implicated pathogenesis via the assessment of T and B cell subsets in different activity phases or with immune effects combined with the analyses of clinical parameters.

Methods

Fifty-eight gout patients and 56 age- and sex-matched healthy individuals were enrolled. To learn the roles of circulating T cells, a lymphocyte profile incorporating 32 T cell subsets was tested from isolated freshly peripheral blood monocyte cells (PBMCs) with multiple-color flow cytometry. Furthermore, the collected clinical features of participants were used to analyze the characteristics of these differential cell subsets. Stratified on the basis of the level of creatinine (Cr, enzymatic method), all patients were categorized into Cr^low (Cr ≤ 116 μmol/L) and Cr^hi (Cr > 116 μmol/L) groups to exploit whether these gout-associated T cell subsets were functional in gout-targeted kidney dysfunction. The differentiation of B cells was investigated in gout patients.

Results

Our results show that CD 4⁺ T cells, Th2 cells, and Tc2 cells were upregulated, whereas Tc17 cells were downregulated. Tfh cells skewed toward the polarization of Tfh2 cells. Specifically, Tfh2 cells increased, but Tfh1 cells decreased, accompanied with aging for gout patients, suggesting that age might trigger the skewing of Tfh1/Tfh2 cell subsets to influence gout development. Moreover, Tfh2 cells were connected to renal dysfunction as well. No alterations of B cell subsets were observed in patients when compared to controls.

Conclusions

Our data demonstrate age-specific dysfunctions of Tfh1/2 cells in gout occurrence, and Tfh2 cell upregulation is associated with gout-targeted renal dysfunction. However, Tfh2 cells may function in auto-inflammatory gout independent of helping B differentiation, and an in-depth study remains to be conducted.

Clinical features and recurrent attack in gout patients according to serum urate levels during an acute attack

BACKGROUND/AIMS

A substantial portion of gout patients have normal serum urate levels during an acute attack but data on the clinical characteristics and risk of recurrence compared with hyperuricemic patients are limited.

METHODS

In this retrospective cohort study, clinical features of normouricemic and hyperuricemic patients were compared. Multivariate analysis was performed to determine whether normouricemic patients were less likely to have a recurrent attack.

RESULTS

Among a total of 221 gout patients, 88 (39.8%) had normouricemia during an acute attack. Postsurgical gout (22.7% vs. 6.0%, p < 0.001), hemodialysis initiation (9.1% vs. 2.3%, p = 0.029) and inflammatory activity were higher in normouricemic patients than in hyperuricemic patients. The frequency of renal insufficiency was lower in normouricemic patients (25.0% vs. 53.4%, p < 0.001). However, the recurrence rate of gout attack was not different between the two groups (24.7% vs. 33.0%, p = 0.220). In multivariate analysis, female sex, history of urinary stone, presence of tophi, and use of thiazide were associated with increase of recurrent gout attack, but not with serum urate status during an acute attack (hazard ratio, 1.075; 95% confidence interval, 0.972 to 1.190; p = 0.159).

CONCLUSION

Normouricemia during an acute gout attack was more frequently observed in postsurgical episodes, hemodialysis initiation and patients with preserved renal function. While higher inflammatory activity was observed in normouricemic patients, recurrent attack was not associated with serum urate levels during an acute attack. Thus, careful follow-up should be considered in gout patients regardless of serum urate levels during an acute attack.

Role of the Gut Microbiome in Uremia: A Potential Therapeutic Target

Also known as the "second human genome," the gut microbiome plays important roles in both the maintenance of health and the pathogenesis of disease. The symbiotic relationship between host and microbiome is disturbed due to the proliferation of dysbiotic bacteria in patients with chronic kidney disease (CKD). Fermentation of protein and amino acids by gut bacteria generates excess amounts of potentially toxic compounds such as ammonia, amines, thiols, phenols, and indoles, but the generation of short-chain fatty acids is reduced. Impaired intestinal barrier function in patients with CKD permits translocation of gut-derived uremic toxins into the systemic circulation, contributing to the progression of CKD, cardiovascular disease, insulin resistance, and protein-energy wasting. The field of microbiome research is still nascent, but is evolving rapidly. Establishing symbiosis to treat uremic syndrome is a novel concept, but if proved effective, it will have a significant impact on the management of patients with CKD.

Association of kidney disease with prevalent gout in the United States in 1988-1994 and 2007-2010

OBJECTIVE

To determine the prevalence of gout associated with progressive degrees of kidney disease in the US population.

METHODS

We performed a cross-sectional analysis among non-institutionalized adults (age 20 and older) of the National Health and Nutrition Examination Surveys in 1988-1994 and 2007-2010. Gout status was ascertained by self-report of physician-diagnosed gout. Chronic kidney disease (CKD) was defined in stages based on estimated glomerular filtration rate (GFR) and single albuminuria measurements (albumin-to-creatinine ratio). Prevalence ratios comparing successive categories of GFR, albuminuria, and CKD as well as temporal trends over a 22-year interval were determined via Poisson regression.

RESULTS

In the US, the crude prevalence of gout was 2-3% among participants without CKD, 4% among participants with CKD stage 1, 6-10% for stage 2, 11-13% for stage 3, and over 30% for stage 4. The adjusted prevalence ratio comparing the CKD stage 4 stratum to participants without CKD was 3.20 (95% CI: 1.96, 5.24) in 2007-2010 and remained significant even after adjustment for serum uric acid. Notably, there was a statistically significant, progressively greater adjusted prevalence ratio of gout associated with successively lower categories of GFR and higher categories of albuminuria.

CONCLUSIONS

Among US adults, there exists a strong dose-response association between impaired renal function and prevalent gout. Health providers should be aware of the elevated burden of gout among patients with CKD especially when evaluating new onset joint pain and swelling.

Dietary and lifestyle factors and medical conditions associated with urinary citrate excretion

BACKGROUND AND OBJECTIVES

Lower urinary citrate excretion is a risk factor for nephrolithiasis and associated with metabolic acidosis and higher prevalence of hypertension and insulin resistance. This study sought to quantify the independent predictors of urinary citrate excretion in population-based cohorts.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional study of 2561 individuals from the Health Professionals Follow-Up Study and Nurses' Health Studies I and II who provided two 24-hour urine collections was conducted. Dietary data were ascertained from the semiquantitative food frequency questionnaire. Lifestyle and disease data were derived from responses to biennial questionnaires. Multivariable linear regression was used to quantify the predictors of urinary citrate excretion.

RESULTS

After adjusting for age, urinary creatinine, dietary, and other factors, higher intake of nondairy animal protein (per 10 g/d; -20 mg/d; 95% confidence interval [-29 to -11]), higher body mass index (per 1 kg/m(2); -4 mg/d; [-6 to -2]), and history of nephrolithiasis (-57 mg/d; [-79 to -36]), hypertension (-95 mg/d; [-119 to -71]), gout (-104 mg/d; [-155 to -54]), and thiazide use (-34 mg/d; [-68 to -1]) were independently associated with lower 24-hour urinary citrate excretion. Higher intake of potassium (per 1000 mg/d; 53 mg/d; [33 to 74]), higher urinary sodium (per 100 mEq/d; 56 mg/d; [31 to 80]), and history of diabetes (61 mg/d; [21 to 100]) were independently associated with higher citrate excretion.

CONCLUSIONS

Several dietary and lifestyle factors and medical conditions are independently associated with urinary citrate excretion.

Alkalizer administration improves renal function in hyperuricemia associated with obesity

We evaluated the combination effect of the alkalizer citrate with the xanthine oxidase inhibitor allopurinol on renal function and uric acid in patients with hyperuricemia associated with obesity and/or metabolic syndrome (MetS), who were extracted from among the subjects enrolled in a prospective randomized controlled study aimed at assessing the efficacy of such a combination for improving renal function. We also conducted a post hoc analysis to examine influences on lipid profiles.

Patients who consented to participate in the study were randomly allocated to receive either allopurinol alone (monotherapy) or in combination with a citrate preparation (combination therapy). The analysis population consisted of 31 obese patients with a body mass index greater than 25 kg/m² (monotherapy, 15 patients; combination therapy, 16 patients). The creatinine clearance rate (Ccr), serum uric acid levels, and lipid profiles were measured before and at 12 weeks after the start of treatment.

In the combination therapy group, Ccr increased significantly and serum uric acid levels decreased significantly in obese patients, while Ccr tended to increase and serum uric acid levels decreased, though not significantly, in patients with MetS-related clinical parameters. Overall, blood triglyceride levels tended to improve in the combination therapy group as compared with the monotherapy group.

Allopurinol to Febuxostat: How far have we come?

For decades allopurinol has been used as a xanthine oxidase inhibitor for treatment of hyperuricemia and gout. Although effective in many patients, some experience sensitivity to the drug. In some cases, this sensitivity may lead to allopurinol hypersensitivity disorder, which if untreated can be fatal. Recently the Food and Drug Administration has approved the use of febuxostat as an alternative therapy for hyperuricemia and gout. Febuxostat is a new xanthine oxidase inhibitor, but is not purine based and therefore decreases adverse reactions due to patient sensitivity. This review is a comprehensive look at the background of hyperuricemia and gout treatment with allopurinol compared to recent clinical studies with febuxostat. Each clinical study is evaluated and summarized, identifying the advances in treatment that have been made as well as the concerns that still exist with either treatment.

Role of the urate transporter SLC2A9 gene in susceptibility to gout in New Zealand Māori, Pacific Island, and Caucasian case-control sample sets

OBJECTIVE

To examine the role of genetic variation in the renal urate transporter SLC2A9 in gout in New Zealand sample sets of Māori, Pacific Island, and Caucasian ancestry and to determine if the Māori and Pacific Island samples could be useful for fine-mapping.

METHODS

Patients (n= 56 Māori, 69 Pacific Island, and 131 Caucasian) were recruited from rheumatology outpatient clinics and satisfied the American College of Rheumatology criteria for gout. The control samples comprised 125 Māori subjects, 41 Pacific Island subjects, and 568 Caucasian subjects without arthritis. SLC2A9 single-nucleotide polymorphisms rs16890979 (V253I), rs5028843, rs11942223, and rs12510549 were genotyped (possible etiologic variants in Caucasians).

RESULTS

Association of the major allele of rs16890979, rs11942223, and rs5028843 with gout was observed in all sample sets (P = 3.7 x 10(-7), 1.6 x 10(-6), and 7.6 x 10(-5) for rs11942223 in the Māori, Pacific Island, and Caucasian samples, respectively). One 4-marker haplotype (1/1/2/1; more prevalent in the Māori and Pacific Island control samples) was not observed in a single gout case.

CONCLUSION

Our data confirm a role of SLC2A9 in gout susceptibility in a New Zealand Caucasian sample set, with the effect on risk (odds ratio >2.0) greater than previous estimates. We also demonstrate association of SLC2A9 with gout in samples of Māori and Pacific Island ancestry and a consistent pattern of haplotype association. The presence of both alleles of rs16890979 on susceptibility and protective haplotypes in the Māori and Pacific Island sample is evidence against a role for this nonsynonymous variant as the sole etiologic agent. More extensive linkage disequilibrium in Māori and Pacific Island samples suggests that Caucasian samples may be more useful for fine-mapping.

The alkalizer citrate reduces serum uric Acid levels and improves renal function in hyperuricemic patients treated with the xanthine oxidase inhibitor allopurinol

OBJECTIVE

Hyperuricemia, an integral component of metabolic syndrome, is a major health problem causing gout and renal damage. Urine alkalizers such as citrate preparations facilitate renal excretion of the uric acid, but its supportive effect on xanthine oxidase inhibitors has not been tested yet. We performed a randomized, prospective study of the effect of a combination of allopurinol and a citrate preparation on renal function in patients with hyperuricemia, employing 70 patients who had hyperuricemia with serum uric acid levels ≥7.0 mg/dL, or those diagnosed as having hyperuricemia in the past.

METHODS

They were randomly enrolled into two study groups: the allopurinol monotherapy (MT) group or combination treatment (CT) group with allopurinol and a citrate preparation. Allopurinol (100-200 mg/day) in the absence or presence of a citrate preparation (3 g/day) was administered for 12 weeks and levels of serum uric acid, its urinary clearance (Cua), and the renal glomerular filtration rates assessed with the creatinine clearance (Ccr) were evaluated before and after the treatment.

RESULTS

Serum levels of uric acid decreased significantly in both groups, whereas the change observed was much greater in CT group. Cua was significantly increased in CT group but not in MT group. Ccr was not altered in both groups in general, whereas it was significantly increased in a fraction of CT group with decreased renal function.

CONCLUSIONS

These results indicate that an additional use of citrate preparations with xanthine oxidase inhibitors is beneficial for patients with hyperuricemia, reducing circulating uric acid and improving their glomerular filtration rates.

Crystal ball gazing: new therapeutic targets for hyperuricaemia and gout

Recent studies in diverse disciplines have led to significant advances in the understanding of the basic biology of hyperuricaemia and gout, with important implications for future treatment. These findings include genetic variation within SLC2A9 as a key regulator of urate homeostasis, and identification of urate-anion exchanger urate transporter 1 (URAT1) and other renal uric acid transporters. Recognition of urate as an endogenous danger signal and activator of the adaptive immune response suggests an important role for urate crystals in non-microbial immune surveillance. The central role of NALP3 inflammasome activation and IL-1beta signalling in the initiation of the acute gout attack raises the possibility of new therapeutic targets. Disordered osteoclastogenesis in patients with chronic gout highlights potential therapies for prevention of joint damage. This review summarizes these findings and the potential relevance for future management of gout.

Uric Acid and renal disease

The interrelationship between uric acid and renal disease is reviewed in a historical context. Four phases can be distinguished--the descriptions of uric acid stones and gravel in the eighteenth century, of chronically scarred kidneys containing urate crystals in the nineteenth, the appearance of the syndrome of acute urate nephropathy following tumour lysis in the mid twentieth century, and finally the realization that soluble urate affects both systemic and glomerular blood vessels, and may play a role in both hypertension and chronic renal damage.

Epidemiology of crystal arthropathy

Gout is an inflammatory arthritis mediated by the crystallization of uric acid within the joints and often is associated with hyperuricemia. Data suggest that the overall disease burden of gout remains substantial and may be increasing. Identifying and characterizing modifiable risk factors for gout is a major step in preventing and managing this painful condition. As more scientific data on the risk factors and comorbidities of gout become available, their integration into gout prevention and care strategies may become essential. This article reviews the relevant epidemiologic data, with a focus on recent progress and data on other crystal arthropathies.

Purine-rich foods, dairy and protein intake, and the risk of gout in men

BACKGROUND

Various purine-rich foods and high protein intake have long been thought to be risk factors for gout. Similarly, the possibility that the consumption of dairy products has a role in protecting against gout has been raised by metabolic studies. We prospectively investigated the association of these dietary factors with new cases of gout.

METHODS

Over a 12-year period, we prospectively examined the relationship between purported dietary risk factors and new cases of gout among 47,150 men who had no history of gout at base line. We used a supplementary questionnaire to ascertain whether participants met the American College of Rheumatology survey criteria for gout. Diet was assessed every four years by means of a food-frequency questionnaire.

RESULTS

During the 12 years of the study, we documented 730 confirmed new cases of gout. The multivariate relative risk of gout among men in the highest quintile of meat intake, as compared with those in the lowest quintile, was 1.41 (95 percent confidence interval, 1.07 to 1.86; P for trend = 0.02), and the corresponding relative risk associated with seafood intake was 1.51 (95 percent confidence interval, 1.17 to 1.95; P for trend = 0.02). In contrast, the incidence of gout decreased with increasing intake of dairy products; the multivariate relative risk among men in the highest quintile, as compared with those in the lowest quintile, was 0.56 (95 percent confidence interval, 0.42 to 0.74; P for trend <0.001). The level of consumption of purine-rich vegetables and the total protein intake were not associated with an increased risk of gout.

CONCLUSIONS

Higher levels of meat and seafood consumption are associated with an increased risk of gout, whereas a higher level of consumption of dairy products is associated with a decreased risk. Moderate intake of purine-rich vegetables or protein is not associated with an increased risk of gout.

Acute uric acid nephropathy in two gouty patients with moderate hyperuricemia and high urine acidity

Acute uric acid nephropathy has been described almost uniformly in patients with massive uric acid overload (malignancies with rapid cell destruction, epileptic seizures). Severe hyperuricosuria and intratubular uric acid precipitation result. Here we present two patients with gout, normal uric acid production, and moderate hyperuricemia, both of whom developed acute uric acid nephropathy. Because of pronounced urine acidity (pH values of 4.6 and 5.0 in morning fasting urines), supersaturation with respect to undissociated uric acid exceeded solubility (0.54 mmol/l), despite basal urate secretions of less than 2.2 mmol/24 hours. Additional predisposing factors, such as uricosuric treatment, heavy beer-drinking, over-consumption of purine-rich foods, and hot environment, were superimposed in both cases.

Renal handling of uric acid in gout: impaired tubular transport of urate not dependent on serum urate levels

Metabolic studies were conducted in 56 patients with primary gout and in ten normal subjects to assess differences in the tubular transport mechanisms of urate. Renal handling of uric acid was examined by means of pyrazinamide and probenecid tests at increased and pharmacologically reduced serum urate concentrations in both groups. Patients with gout showed similar serum urate levels and glomerular filtration rates than controls at both serum urate levels. Pyrazinamide decreased urinary uric acid excretion to less than 1.0% of the urate filtered load in both groups at increased and diminished serum urate concentrations. The maximum uricosuric response promoted by probenecid at high serum urate levels was (mean +/- SD) 3,707 +/- 443 micrograms/min/1.73 m2 in controls and 2,215 +/- 738 micrograms/min/1.73 m2 in patients with gout (P less than 0.01). Forty-four patients had a daily uric acid excretion rate below 700 mg/1.73 m2, and all of them showed a diminished uricosuric response to probenecid. When serum urate was reduced in normal subjects and 30 patients to a mean of 2.1 and 2.3 mg/dL, respectively, probenecid elicited a significantly lower urate excretion rate in gout (532 +/- 202 micrograms/min/1.73 m2) than in controls (922 +/- 136 micrograms/min/1.73 m2; P less than 0.01). Among these 30 patients examined in their basal state and at decreased serum urate levels, uric acid excretion following probenecid was normal in six and diminished in 24 in both situations. The difference between maximum uricosuria and basal urate excretion was not increased in gouty patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A controlled study of diet in patients with gout

To determine whether patients with gout have a diet which is distinctive in quality or quantity a careful dietary questionnaire was posed over 7 days to 61 men with gout and 52 control subjects. The average daily intake of most nutrients, including total purine nitrogen, was similar except that the patients with gout drank significantly more alcohol. Beer was the most popular beverage, and 25 (41%) of those with gout consumed more than 60 g alcohol daily (equivalent to 2 . 5 litres of beer). The heavy drinkers had a significantly higher intake of purine nitrogen, half of which was derived from beer. Though the effect of ingested purine on the blood uric acid is difficult to estimate, it probably was sufficient to have a clinical effect, augmenting the hyperuricaemic effect of alcohol itself.

Allopurinol treatment and its effect on renal function in gout: a controlled study

Fifty-nine patients with primary gout were treated with either a combination of colchicine and allopurinol or colchicine alone. Assessments of renal function over 2 years revealed a statistically significant fall of glomerular filtration rate an urine concentrating ability in those receiving only colchicine. The renal function of patients given allopurinol did not change. Treatment with allopurinol resulted ina significant reduction of ammonium excretion, a phenomenon which could not be readily explained. Urate clearance also declined during allopurinol treatment, and the impaired urate clearance associated with gout became more evident. The most important observation was that allopurinol retarded an apparent decline of renal function. Presumably this was achieved through its hypouricaemic effect and implies that the hyperuricaemia of gouty patients is deleterious to the kidneys.