Exercise-induced acute renal failure associated with renal hypouricaemia: results of a questionnaire-based survey in Japan

Acute Renal Failure with Severe Loin Pain and Patchy Renal Ischemia after Anaerobic Exercise in Active Duty Marines

Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE) is a rare cause of exertional acute kidney injury. The proposed mechanism of injury in ALPE is renovascular spasm, in the setting of oxidative stress and muscular damage, which creates a characteristic wedge-shaped infarction pattern on delayed imaging. Patients present with nausea, vomiting, loin or abdominal pain, and fatigue within 1-2 days of anaerobic exercise, associated with an acute rise in serum creatinine, which generally plateaus within 3 days. This process is likely exacerbated by dehydration, analgesic usage, and lower baseline fitness levels. This disease process is distinct from rhabdomyolysis, in that creatine kinase levels are not significantly elevated, myoglobinuria is not seen, and aggressive fluid resuscitation is not beneficial. We present three cases of ALPE following participation in the Marine Combat Fitness Test (CFT), an anaerobic evolution. Medical workup demonstrated no additional etiology for acute renal failure. The average peak creatinine in these patients was 2.9 mg/dL, and all demonstrated return to normal renal function, without hemodialysis. One patient experienced recurrent ALPE, after short-interval CFT participation. Military medical providers should be aware of this diagnosis when evaluating service members with acute renal injury after exercise. The clinical course is benign, and affected service members are at increased risk of recurrence, with subsequent intense exercise. Service members should engage in a graduated exercise program, before intense exercise activities, and should be monitored closely for recurrent renal injury.

Genotype and Phenotype of Renal Hypouricemia: A Single-Center Study from China

BACKGROUND

Renal hypouricemia (RHUC), a rare inherited disorder characterized by impaired uric acid reabsorption and subsequent profound hypouricemia, occurs mainly due to variants in SLC22A12 or SLC2A9. Only anecdotal cases and one small-scale RHUC screening study have been reported in the Chinese population.

METHODS

A total of 19 patients with RHUC from 17 unrelated families were recruited from our center. The medical history, clinical manifestations, biochemical exam, and clinical outcomes were collected. Next-generation sequencing-based targeted gene sequencing or whole exon sequencing was performed.

RESULTS

A total of 22 variants in SLC22A12 or SLC2A9 were found in 19 patients. The variant c.944G>A (p.W315X) in SLC2A9 was identified in three patients. Three variants c.165C>A (p.D55E), c.1549_1555delGAGACCC (p.E517Rfs*17), and c.1483T>C (p.W495R) in SLC22A12 and three variants c.1215+1G>A (splicing variant), c.643A>C (p.T215P), and c.227C>A (p.S76X) in SLC2A9 were novel. A proportion of 10 out of 19 patients presented with exercise-induced acute kidney injury (EIAKI). The renal outcome was favorable. Five patients had nephrolithiasis, in whom three had hypercalciuria.

CONCLUSION

The current study reported six novel variants in SLC22A12 and SLC2A9 genes of Chinese patients with RHUC. The variant c.944G>A (p.W315X) in SLC2A9 may be common in Chinese patients. EIAKI is the main clinical phenotype associated with RHUC in our cohort, with a favorable outcome. Hypercalciuria presented in some RHUC patients is a new finding.

Recurrent exercise-induced acute kidney injury associated with hypouricemia: a case report and literature review

BACKGROUND

Hereditary renal hypouricemia (RHUC) is a heterogenous disorder characterized by defective uric acid (UA) reabsorption resulting in hypouricemia and increased fractional excretion of UA. RHUC is an important cause of exercise-induced acute kidney injury (EIAKI), nephrolithiasis and posterior reversible encephalopathy syndrome (PRES). We present here an unusual case of a patient with RHUC who presented with recurrent EIAKI and had two heterozygous mutations in the SLC2A9 gene.

CASE PRESENTATION

A 43-year old man was admitted to our clinic because of bilateral loin pain, nausea and sleeplessness for 3 days after strenuous exercise. The laboratory results revealed increased levels of blood urea nitrogen (BUN) (15 mmol/l) and serum creatinine (Scr) (450 μmol/l), while the UA level was extremely low at 0.54 mg/dl, and his fractional excretion of urate (FE-UA) was 108%. The patient had an episode of acute kidney injury after playing soccer approximately 20 years ago, and on routine physical examination, his UA was less than 0.50 mg/dl. In view of the marked hypouricemia and high FE-UA, a diagnosis of RHUC was suspected, which led us to perform mutational screening of the SLC22A12 and SLC2A9 genes. DNA sequencing revealed no mutation in SLC22A12 gene, but two heterozygous mutations in the SLC2A9 gene.

CONCLUSIONS

This is a rare report of a patient with RHUC2 due to the mutation of SLC2A9. And this unique symptom of EIAKI and decreased or normal serum concentrations of UA warrant more attention as an early cue of RHUC.

J-shaped Association between Serum Uric Acid Levels and the Prevalence of a Reduced Kidney Function: A Cross-Sectional Study Using Japanese Health Examination Data

Objective While an association between a reduced kidney function and hyperuricemia has been reported, its association with hypouricemia is not well understood. The present study therefore investigated this association. Methods Using a large Japanese health examination dataset, we performed a multivariable logistic regression analysis to assess the association between serum uric acid (SUA) levels and a reduced kidney function. The covariates included the age, body mass index, alcohol intake, and the presence of hypertension, dyslipidemia, or diabetes. Patients This study included 227,672 patients (104,854 men; 46.1%), and the analyses were performed separately for men and women. The patients were classified into 5 groups: hypouricemia (SUA ≤2.0 mg/dL) (1st) and four other (2nd-5th) groups with SUA levels of ≤2.0, 2.1-5.1, 5.2-5.9, 6.0-6.8, ≥6.9 mg/dL in men and ≤2.0, 2.1-3.7, 3.8-4.4, 4.5-5.1, ≥5.2 mg/dL in women, respectively. Results The characteristics of the study population were as follows: men, age 55.9±14.9 years old, SUA 5.9±1.3 mg/dL, estimated glomerular filtration rate (eGFR) 80.0±17.2 mL/min/1.73 m2, and a reduced kidney function (eGFR<60.0 mL/min/1.73 m2) 9.4%; women, age 57.3±15.0 years old, SUA 4.5±1.1 mg/dL, eGFR 81.2±18.0 mL/min/1.73 m2, and a reduced kidney function 9.4%. Compared with the 2nd group, the other 4 groups groups had a significantly higher prevalence of a reduced kidney function [odds ratio (OR), 2.58; 95% confidence interval (CI), 1.64-4.06 in men; OR, 1.66; 95% CI, 1.16-2.39 in women]. Conclusion The prevalence of a reduced kidney function was high in both men and women in the hypouricemia and high-SUA groups. SUA levels and the prevalence of a reduced kidney function showed a J-shaped association.

Possible Use of Non-purine Selective Xanthine Oxidoreductase Inhibitors for Prevention of Exercise-induced Acute Kidney Injury Associated with Renal Hypouricemia

Exercise-induced acute kidney injury (EIAKI) is frequently complicated with renal hypouricemia (RHUC). In patients with RHUC, limiting anaerobic exercise can prevent EIAKI. However, it is challenging to reduce exercise intensity in athletes. We herein report a 16-year-old Japanese football player with familial RHUC with compound heterozygous mutations in urate transporter 1 (URAT1) who presented with recurrent EIAKI. As prophylaxis (hydration during exercise) could not prevent EIAKI, febuxostat was initiated. EIAKI was not observed for 16 months despite exercising intensively. Hence, non-purine-selective xanthine oxidoreductase inhibitors may decrease the incidence of EIAKI in athletes with RHUC.

Increased prevalence of periodontitis with hypouricemic status: findings from the Korean National Health and Nutrition Examination Survey, 2016-2018

PURPOSE

The aim of this study was to investigate the relationship between serum uric acid (SUA) levels and the risk of periodontitis in Korean adults using data from the Korean National Health and Nutrition Examination Survey (KNHANES).

METHODS

This cross-sectional study used data from the KNHANES 2016-2018 and analysed 12,735 Korean adults aged ≥19 years who underwent oral examinations. Hypouricemia was defined as SUA <3 mg/dL in men and <2 mg/dL in women, and hyperuricemia was defined as SUA ≥7 mg/dL in men and ≥6 mg/dL in women.

RESULTS

The weighted prevalence of hypouricemia and hyperuricemia was 0.6% and 12.9%, respectively. The overall weighted periodontitis rate was 30.5%. The frequency of periodontitis in subjects with hypouricemia, normouricemia, and hyperuricemia were 51.1%, 30.3%, and 30.6%, respectively. Study participants with hypouricemia were significantly older, had significantly fasting blood glucose levels, and had better kidney function than non-hypouricemic participants. In univariate logistic regression analyses, hypouricemia was associated with periodontitis, but hyperuricemia was not. The fully adjusted model revealed that the adjusted odds ratio of hypouricemia for periodontitis was 1.62 (95% confidence interval, 1.13-2.33), while the relationship between hyperuricemia and periodontitis in the multivariable logistic regression model was not significant.

CONCLUSIONS

The results of this study suggest that hypouricemia is associated with an increased risk of periodontitis.

Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise

BACKGROUND

There are two known types of exercise-induced acute renal failure. One is the long-known myoglobinuria-induced acute renal failure due to severe rhabdomyolysis, and the other is the recently recognized non-myoglobinuria-induced acute renal failure with mild rhabdomyolysis. Exercise-induced acute renal failure was first reported in 1982. Non-myoglobinuria-induced acute renal failure is associated with severe low back pain and patchy renal vasoconstriction, and it is termed post-exercise acute renal failure because it usually occurs hours after exercise. It is also called acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE).

AIM

To makes a significant contribution to medical literature as it presents a study that investigated a not-widely-known type of exercise-induced acute renal failure known as ALPE.

METHODS

We performed a database search selecting papers published in the English or Japanese language. A database search was lastly accessed on September 1, 2022. The results of this study were compared with those reported in other case series.

RESULTS

The study evaluated renal hypouricemia as a key risk factor of ALPE. The development of ALPE is due to the sum of risk factors such as exercise, hypouricemia, nonsteroidal anti-inflammatory drugs, vasopressors, and dehydration.

CONCLUSION

In conclusion, hypouricemia plays a key role in the development of ALPE and is often associated with anaerobic exercise. The development of ALPE is a result of the cumulative effects of risk factors such as exercise, hypouricemia, NSAIDs, vasopressors, and dehydration.

Prevalence and factors related to hypouricemia and hyperuricemia in schoolchildren: results of a large-scale cross-sectional population-based study conducted in Japan

Hypouricemia in children including renal hypouricemia, which is a major cause of exercise-induced acute renal injury (EIAKI), is an important clinical problem, in addition to hyperuricemia. However, no large-scale studies of serum uric acid (UA) concentrations in the general pre-adolescent population have been carried out. We conducted a population-based cross-sectional study to measure the prevalences of hypouricemia and hyperuricemia and identify the associated factors. We analyzed 31,822 (16,205 boys and 15,617 girls) 9-10-year-old children who underwent pediatric health check-ups in Kagawa prefecture between 2014 and 2018. Hypouricemia and hyperuricemia were defined using serum UA concentrations of ≤ 2.0 mg/dL and ≥ 6.0 mg/dL, respectively. The prevalence of hypouricemia was 0.38% in both 9- and 10-year-old boys and girls, and was not significantly associated with age, sex, or environmental factors, including overweight. The prevalence of hyperuricemia was significantly higher in boys (2.7%) than in girls (1.9%), and was significantly associated with age, overweight, future diabetes risk, hypertriglyceridemia, low high-density lipoprotein-cholesterol, and liver damage, but not with high low-density lipoprotein cholesterol. Therefore, some pre-adolescent children in the general population in Japan showed hypouricemia. A means of identifying children with hypouricemia and lifestyle guidance measures for the prevention of EIAKI should be established.

Lack of xanthine dehydrogenase leads to a remarkable renal decline in a novel hypouricemic rat model

Uric acid (UA) is the final metabolite in purine catabolism in humans. Previous studies have shown that the dysregulation of UA homeostasis is detrimental to cardiovascular and kidney health. The Xdh gene encodes for the Xanthine Oxidoreductase enzyme group, responsible for producing UA. To explore how hypouricemia can lead to kidney damage, we created a rat model with the genetic ablation of the Xdh gene on the Dahl salt-sensitive rat background (SS^Xdh−/−). SS^Xdh−/− rats lacked UA and exhibited impairment in growth and survival. This model showed severe kidney injury with increased interstitial fibrosis, glomerular damage, crystal formation, and an inability to control electrolyte balance. Using a multi-omics approach, we highlighted that lack of Xdh leads to increased oxidative stress, renal cell proliferation, and inflammation. Our data reveal that the absence of Xdh leads to kidney damage and functional decline by the accumulation of purine metabolites in the kidney and increased oxidative stress.

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A novel rat model of hypouricemia was created by the gene ablation of the Xdh gene

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The SS^Xdh-/- rat showed a failure to thrive, kidney injury, and functional decline

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Multi-omics revealed increased inflammation and oxidative stress in SS^Xdh-/- rats

Genetic Basis of the Epidemiological Features and Clinical Significance of Renal Hypouricemia

A genetic defect in urate transporter 1 (URAT1) is the major cause of renal hypouricemia (RHUC). Although RHUC is detected using a serum uric acid (UA) concentration <2.0 mg/dL, the relationship between the genetic state of URAT1 and serum UA concentration is not clear. Homozygosity and compound heterozygosity with respect to mutant URAT1 alleles are associated with a serum UA concentration of <1.0 mg/dL and are present at a prevalence of ~0.1% in Japan. In heterozygous individuals, the prevalence of a serum UA of 1.1−2.0 mg/dL is much higher in women than in men. The frequency of mutant URAT1 alleles is as high as 3% in the general Japanese population. The expansion of a specific mutant URAT1 allele derived from a single mutant gene that occurred in ancient times is reflected in modern Japan at a high frequency. Similar findings were reported in Roma populations in Europe. These phenomena are thought to reflect the ancient migration history of each ethnic group (founder effects). Exercise-induced acute kidney injury (EI-AKI) is mostly observed in individuals with homozygous/compound heterozygous URAT1 mutation, and laboratory experiments suggested that a high UA load on the renal tubules is a plausible mechanism for EI-AKI.

Hypouricemia and Urate Transporters

Hypouricemia is recognized as a rare disorder, defined as a serum uric acid level of 2.0 mg/dL or less. Hypouricemia is divided into an overexcretion type and an underproduction type. The former typical disease is xanthinuria, and the latter is renal hypouricemia (RHUC). The frequency of nephrogenic hypouricemia due to a deficiency of URAT1 is high in Japan, accounting for most asymptomatic and persistent cases of hypouricemia. RHUC results in a high risk of exercise-induced acute kidney injury and urolithiasis. It is vital to promote research on RHUC, as this will lead not only to the elucidation of its pathophysiology but also to the development of new treatments for gout and hyperuricemia.

J-shaped Relationship Between Chronic Kidney Disease and Serum Uric Acid Levels: A Cross-sectional Study on the Korean Population

Objective

Both hypouricemia and hyperuricemia are reportedly associated with reduced kidney function This study investigated the association between uric acid levels and the risk of reduced renal function in men and women.

Methods

We conducted a cross-sectional study using data from a government-funded health examinee cohort of a Korean genome and epidemiological study A total of 172,970 participants (58,981 men, 113,989 women) aged 40∼79 years were included A logistic regression test was performed, and the odds ratio (OR) and 95% confidence interval (CI) were calculated to examine the relationship between stratified uric acid levels and the frequency of chronic kidney disease.

Results

As the uric acid level increased, the risk of reduced renal function increased Moreover, for uric acid levels ≤20 mg/dL, the risk of reduced renal function was higher than that of the reference group Among the total, man, and woman groups, a statistically significant association was observed in men (OR 171, 95% CI 0945∼3111, OR 5003, 95% CI 1405∼17809, and OR 1377, 95% CI 0696∼2724, respectively).

Conclusion

The OR of reduced renal function according to uric acid levels formed a J-shaped curve in both genders.

Recurrent Acute Kidney Injury with Severe Loin Pain and Patchy Renal Ischaemia after Anaerobic Exercise without Renal Hypouricaemia in a New Zealand European Male

Acute kidney injury with severe loin pain and patchy renal ischaemia after anaerobic exercise (ALPE) is a rare clinical syndrome. ALPE has predominantly been described in Japanese and Korean populations to date. Many cases and most recurrent examples are associated with renal hypouricaemia. We describe a 28-year-old New Zealand European male without renal hypouricaemia who developed recurrent ALPE whilst performing elite-level sport. Avoiding elite-level anaerobic exercise was successful at preventing further episodes. This report confirms the first known case of ALPE in a New Zealand European male and raises the possibility that ALPE is an under-recognized condition. Long-term outcomes of recurrent ALPE remain unclear, and preventative strategies should be implemented to preserve renal function. Avoiding intense anaerobic exercise is an effective preventative strategy.

J-shaped curve for the association between serum uric acid levels and the prevalence of blood pressure abnormalities

Low and high serum uric acid levels are associated with an increased risk of cardiovascular diseases. However, whether there is a similar association between serum uric acid levels and blood pressure abnormalities has not yet been elucidated. Data from 236,221 individuals (age, 56.0 ± 15.0 years; 107,146 men) who underwent routine health checkups were analyzed. Participants with a serum uric acid level ≤2.0 mg/dL were separated, and the remaining participants were divided into quartiles according to their serum uric acid levels. Among each group, the proportions of participants with high blood pressure (≥130/80 mmHg, and/or medication) and hypertension (≥140/90 mmHg, and/or medication), were calculated. The adjusted odds ratio of each group compared to the group with the lowest proportion of blood pressure abnormalities was calculated. The participants were divided into five groups according to their serum uric acid levels, ≤2.0, 2.1-4.0, 4.1-5.0, 5.1-6.0, and ≥6.1 mg/dL, and the prevalence of high blood pressure was 49.0, 44.6, 52.3, 58.6, and 65.3% and that of hypertension was 31.0, 27.4, 33.5, 38.7, and 43.8%, respectively. Compared to the second-lowest serum uric acid group (2.1-4.0 mg/dL), groups with higher serum uric acid levels (4.1-5.0, 5.1-6.0, and ≥6.1 mg/dL), as well as the group with the lowest serum uric acid level (≤2.0 mg/dL), showed significantly higher odds ratios for high blood pressure and hypertension. High and low serum uric acid levels were significantly associated with an increased prevalence of high blood pressure and followed a J-shaped curve.

The Management of Gout in Renal Disease

Gout, a debilitating inflammatory arthritis, currently affects more than 9 million Americans. Hyperuricemia, the laboratory abnormality associated with the development of gout, also occurs in a significant number of patients with chronic kidney disease (CKD), a condition that affects approximately 14% of the US population. Several recent studies have attempted to provide a definitive link between the presence of hyperuricemia and progression of CKD; however, the treatment of asymptomatic hyperuricemia in CKD is not supported by recent randomized controlled trials. The pharmacology of acute gout flares and urate lowering is complicated in patients who also have evidence of CKD, primarily because of an increased risk of medication toxicity. Recipients of kidney transplants are particularly at risk of debilitating gout and medication toxicity. We review the available data linking CKD, gout, and hyperuricemia, providing practice guidelines on managing gout in CKD patients and kidney transplant recipients. We advocate for much greater involvement of nephrologists in the management of gout in renal patients.

Renal effects of uric acid: hyperuricemia and hypouricemia

The prevalence of chronic kidney disease (CKD) is increasing worldwide. Although hyperuricemia has been associated with CKD in many studies, it remains controversial whether this is the cause or the result of decreased renal function. Recent observational studies of healthy populations and patients with CKD have reported that uric acid (UA) has an independent role in the development or progression of CKD. Experimental studies have shown several potential mechanisms by which hyperuricemia may cause or promote CKD. However, other reports have indicated an association between hypouricemia and CKD. This opposing effect is hypothesized to occur because UA is a major antioxidant in human plasma and is associated with oxidative stress. In this article, we discuss the potential association between UA imbalance and CKD and how they can be treated.

New insights into purine metabolism in metabolic diseases: role of xanthine oxidoreductase activity

Xanthine oxidoreductase (XOR) consists of two different forms, xanthine dehydrogenase and xanthine oxidase (XO), and is a rate-limiting enzyme of uric acid production from hypoxanthine and xanthine. Uric acid is the end product of purine metabolism in humans and has a powerful antioxidant effect. The lack of ascorbic acid, known as vitamin C, in hominoids has been thought to cause a compensatory increase in uric acid as an antioxidant by unfunctional gene mutation of uricase to a pseudogene. Because XO is involved in an increase in reactive oxygen species (ROS) by generating superoxide and hydrogen peroxide, inadequate activation of XOR promotes oxidative stress-related tissue injury. Plasma XOR activity is associated with obesity, smoking, liver dysfunction, hyperuricemia, dyslipidemia, insulin resistance, and adipokines, indicating a novel biomarker of metabolic disorders. However, XOR activity in adipose tissue is low in humans unlike in rodents, and hypoxanthine is secreted from human adipose tissue. The concentration of hypoxanthine, but not xanthine, is independently associated with obesity in a general population, indicating differential regulation of hypoxanthine and xanthine. Treatment with an XOR inhibitor can decrease uric acid for preventing gout, reduce production of XO-related ROS, and promote reutilization of hypoxanthine and ATP production through the salvage pathway. It has recently been suggested that discontinuation of an XOR inhibitor causes adverse cardiovascular outcomes as XOR inhibitor withdrawal syndrome, possibly due to cardiac disturbance of conduction and contraction by reduced ATP production. New insights into purine metabolism, including the role of XOR activity in the past 5 yr, are mainly discussed in this review.

Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise

Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE) is gradually gaining recognition. In this case series, we describe the presentation of ALPE in the emergency department setting and its clinical course. In Case 1, an 18-year-old man presented with acute-onset nausea, vomiting, and right flank pain after playing basketball, with a creatinine level of 6.42 mg/dL on initial presentation. He received fluid therapy and intravenous furosemide for 2 days. His creatinine level was 1.80 mg/dL on day 8 and finally declined to 0.71 mg/dL on day 39. In Case 2, a 31-year-old man presented with acute-onset nausea and right lower abdominal pain after swimming, with a creatinine level of 4.68 mg/dL on initial presentation. He only received fluid therapy, and his creatinine level finally declined to 0.90 mg/dL on day 11. In both cases, severe loin pain began after anaerobic exercise, and acute kidney injury without myoglobinuria was observed. The findings of our case series suggest that emergency physicians should consider ALPE in the differential diagnosis of abdominal and loin pain accompanied by an elevated creatinine level in young patients because it can be treated conservatively and has a good prognosis. Moreover, watchful waiting is recommended for ALPE while also emphasizing the need to exclude potentially life threatening or treatable kidney diseases.

Transplantation of a kidney with a heterozygous mutation in the SLC22A12 (URAT1) gene causing renal hypouricemia: a case report

Background

Renal hypouricemia (RHUC) is a genetic disorder caused by mutations in the SLC22A12 gene, which encodes the major uric acid (UA) transporter, URAT1. The clinical course of related, living donor-derived RHUC in patients undergoing kidney transplantation is poorly understood. Here, we report a case of kidney transplantation from a living relative who had an SLC22A12 mutation. After the transplantation, the recipient’s fractional excretion of UA (FEUA) decreased, and chimeric tubular epithelium was observed.

Case presentation

A 40-year-old man underwent kidney transplantation. His sister was the kidney donor. Three weeks after the transplantation, he had low serum-UA, 148.7 μmol/L, and elevated FEUA, 20.8% (normal: < 10%). The patient’s sister had low serum-UA (101.1 μmol/L) and high FEUA (15.8%) before transplant. Suspecting RHUC, we performed next-generation sequencing on a gene panel containing RHUC-associated genes. A heterozygous missense mutation in the SLC22A12 gene was detected in the donor, but not in the recipient. The recipient’s serum-UA level increased from 148.7 μmol/L to 231.9 μmol/L 3 months after transplantation and was 226.0 μmol/L 1 year after transplantation. His FEUA decreased from 20.8 to 11.7% 3 months after transplantation and was 12.4% 1 year after transplantation. Fluorescence in situ hybridization of allograft biopsies performed 3 months and 1 year after transplantation showed the presence of Y chromosomes in the tubular epithelial cells, suggesting the recipient’s elevated serum-UA levels were owing to a chimeric tubular epithelium.

Conclusions

We reported on a kidney transplant recipient that developed RHUC owing to his donor possessing a heterozygous mutation in the SLC22A12 (URAT1) gene. Despite this mutation, the clinical course was not problematic. Thus, the presence of donor-recipient chimerism in the tubular epithelium might positively affect the clinical course, at least in the short-term.

Extreme hyperuricemia is a risk factor for infection-related deaths in incident dialysis patients: a multicenter prospective cohort study

Introduction

There are few studies on the association between serum uric acid (UA) level and mortality in incident dialysis patients. We aimed to clarify whether the serum UA level at dialysis initiation is associated with mortality during maintenance dialysis.

Methods

We enrolled 1486 incident dialysis patients who participated in a previous multicenter prospective cohort study in Japan. We classified the patients into the following five groups according to their serum UA levels at dialysis initiation: G1 with a serum UA level <6 mg/dL; G2, 6.0–8.0 mg/dL; G3, 8.0–10.0 mg/dL; G4, 10.0–12.0 mg/dL; and G5, ≥12.0 mg/dL. We created three models (Model 1: adjusted for age and sex, Model 2: adjusted for Model 1 + 12 variables, and Model 3: stepwise regression adjusted for Model 2 + 13 variables) and performed a multivariate Cox proportional hazard regression analysis to examine the association between the serum UA level and outcomes, including infection-related mortality.

Results

Hazard ratios (HRs) were calculated relative to the G2, because the all-cause mortality rate was the lowest in G2. For Models 1 and 2, the all-cause mortality rate was significantly higher in G5 than in G2 (HR: 1.63, 95% confidence interval [CI]: 1.14–2.33 and HR: 1.78, 95% CI: 1.19–2.68, respectively). For Models 1, 2, and 3, the infection-related mortality rate was significantly higher in G5 than in G2 (HR: 2.75, 95% CI: 1.37–5.54, HR: 3.09, 95% CI: 1.45–6.59, HR: 3.37, and 95% CI: 1.24–9.15, respectively).

Conclusions

Extreme hyperuricemia (serum UA level ≥12.0 mg/dL) at dialysis initiation is a risk factor for infection-related deaths.

A Case of Acute Kidney Injury in a Patient with Renal Hypouricemia without Intense Exercise

Exercise-induced acute kidney injury (EIAKI) frequently develops in patients with renal hypouricemia (RHUC). However, several cases of RHUC with acute kidney injury (AKI) but without intense exercise have been reported. We encountered a 15-year-old male with RHUC who experienced AKI. He reported no episodes of intense exercise and displayed no other representative risk factors of EIAKI, although a vasopressor had been administered for orthostatic dysregulation before AKI onset. His kidney dysfunction improved with discontinuation of the vasopressor and conservative treatment. Thus, AKI can develop in patients with RHUC in the absence of intense exercise, for which vasopressors may be a risk factor.

Uric acid and inflammation in kidney disease

Asymptomatic hyperuricemia is frequently observed in patients with kidney disease. Although a substantial number of epidemiologic studies have suggested that an elevated uric acid level plays a causative role in the development and progression of kidney disease, whether hyperuricemia is simply a result of decreased renal excretion of uric acid or is a contributor to kidney disease remains a matter of debate. Over the last two decades, multiple experimental studies have expanded the knowledge of the biological effects of uric acid beyond its role in gout. In particular, uric acid induces immune system activation and alters the characteristics of resident kidney cells, such as tubular epithelial cells, endothelial cells, and vascular smooth muscle cells, toward a proinflammatory and profibrotic state. These findings have led to an increased awareness of uric acid as a potential and modifiable risk factor in kidney disease. Here, we discuss the effects of uric acid on the immune system and subsequently review the effects of uric acid on the kidneys mainly in the context of inflammation.

Intensive uric acid-lowering therapy in CKD patients: the protocol for a randomized controlled trial

BACKGROUND

Hyperuricemia would be a risk factor for the development/progression of CKD. However, several studies showed U-shape association between serum uric acid level and renal impairment, suggesting that hypouricemia was rather associated with renal dysfunction. Perhaps, there is the optimal target level of serum UA for renal function.

METHODS

The Target-UA study is a multicenter randomized controlled trial. Eligible CKD patients (eGFR ≥ 30, < 60 mL/min/1.73 m2 and urine protein < 0.5 g/gCr or urine albumin to creatinine ratio (ACR) < 300 mg/gCr) with serum UA ≥ 8.0 mg/dL (≥ 7.0 mg/dl: under the treatment) will be enrolled and be randomly assigned to the intensive therapy group (target serum UA level ≥ 4.0 mg/dL, < 5.0 mg/dL) or the standard therapy group (serum UA level ≥ 6.0 mg/dL, < 7.0 mg/dL). Topiroxostat, a new xanthine oxidase inhibitor, will be administered to treat hyperuricemia. The primary endpoint is a change in logarithmic value of urine ACR between baseline and week 52 of treatment. The secondary endpoints include changes in serum UA, eGFR, urine protein, lipid profile, and onset of composite cardiovascular events, renal events, gouty arthritis, and attack of urolithiasis. The number of subjects has been set to be 185 in each group for a total of 370.

DISCUSSION

This is the first study, to the best of our knowledge, to determine the optimal target level of serum UA for renal protection and is expected to lead to progress in CKD treatment.

TRIAL REGISTRATION

(UMIN000026741 and jRCTs051180146).

Non-urate transporter 1, non-glucose transporter member 9-related renal hypouricemia and acute renal failure accompanied by hyperbilirubinemia after anaerobic exercise: a case report

Background

Renal hypouricemia (RHUC) is an inherited heterogenous disorder caused by faulty urate reabsorption transporters in the renal proximal tubular cells. Anaerobic exercise may induce acute kidney injury in individuals with RHUC that is not caused by exertional rhabdomyolysis; it is called acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE).

RHUC is the most important risk factor for ALPE. However, the mechanism of onset of ALPE in patients with RHUC has not been elucidated. The currently known genes responsible for RHUC are SLC22A12 and SLC2A9.

Case presentation

A 37-year-old man presented with loin pain after exercising. Despite having a healthy constitution from birth, biochemical examination revealed hypouricemia, with a uric acid (UA) level of < 1 mg/dL consistently at every health check. We detected acute kidney injury, with a creatinine (Cr) level of 4.1 mg/dL, and elevated bilirubin; hence, the patient was hospitalized. Computed tomography revealed no renal calculi, but bilateral renal swelling was noted. Magnetic resonance imaging detected cuneiform lesions, indicating bilateral renal ischemia. Fractional excretion values of sodium and UA were 0.61 and 50.5%, respectively. Urinary microscopy showed lack of tubular injury. The patient’s older sister had hypouricemia. The patient was diagnosed with ALPE. Treatment with bed rest, fluid replacement, and nutrition therapy improved renal function and bilirubin levels, and the patient was discharged on day 5. Approximately 1 month after onset of ALPE, his Cr, UA, and TB levels were 0.98, 0.8, and 0.9 mg/dL, respectively. We suspected familial RHUC due to the hypouricemia and family history and performed genetic testing but did not find the typical genes responsible for RHUC. A full genetic analysis was opposed by the family.

Conclusions

To the best of our knowledge, this is the first report of ALPE with hyperbilirubinemia. Bilirubin levels may become elevated as a result of heme oxygenase-1 activation, occurring in exercise-induced acute kidney injury in patients with RHUC; this phenomenon suggests renal ischemia-reperfusion injury. A new causative gene coding for a urate transporter may exist, and its identification would be useful to clarify the urate transport mechanism.

Hypouricemia: what the practicing rheumatologist should know about this condition

We presented an update in the field of hypouricemia, which is defined as a serum urate concentration of < 2 mg/dL (119 μmol/L), for the practicing rheumatologist, who usually is the consulting physician in cases of disorders of urate metabolism. We performed a narrative review through a literature search for original and review articles in the field of human hypouricemia published between January 1950 and July 2018. We divided the etiology of hypouricemia into two main categories: those associated with a decrease in urate production and those promoting the elimination of urate via the kidneys. The most common conditions associated with these categories are discussed. Furthermore, the etiology of hypouricemia may be associated with certain medications prescribed by the practicing rheumatologists, such as the following: urate-lowering drugs (allopurinol and febuxostat); recombinant uricase (pegloticase); uricosuric agents (probenecid, benzbromarone); urate transporter URAT1 inhibitor (lesinurad); angiotensin II receptor blocker (losartan); fenofibrate; high-dose trimethoprim-sulfamethoxazole; some NSAID; and high-dose salicylate therapy. The rheumatologist is considered an expert in the metabolism of urate and its associated pathological conditions. Therefore, specialists must recognize hypouricemia as a biomarker of various pathological and potentially harmful conditions, highlighting the importance of conducting a deeper clinical investigation to reach a more accurate diagnosis and treatment.

Idiopathic renal hypouricemia: A case report and literature review

Idiopathic renal hypouricemia is a rare hereditary condition. Type 2 renal hyperuricemia (RHUC2) is caused by a mutation in the SLC2A9 gene, which encodes a high‑capacity glucose and urate transporter, glucose transporter (GLUT)9. RHUC2 predisposes to exercise‑induced acute renal failure (EIARF) and nephrolithiasis, which is caused by a defect in renal tubular urate transport and is characterized by increased clearance of renal uric acid. In the present study a case of a 35‑year‑old Chinese man with EIARF is reported. The patient had isolated renal hypouricemia, with a serum uric acid level of 21 µmol/l and a fractional excretion of uric acid of 200%. The mutational analysis revealed a homozygous mutation (c.857G>A in exon 8) in the SLC2A9 gene. The patient's family members carried the same mutation, but were heterozygous and clinically asymptomatic. In conclusion, to the best of our knowledge, this is the first report of a RHUC2 patient with a GLUT9 mutation, p.W286X, which may be a pathogenic mutation of RHUC2. Further investigation into the functional role of GLUT9 in this novel SLC2A9 mutation is required.

Exercise-Induced Acute Kidney Injury in a Police Officer with Hereditary Renal Hypouricemia

Hereditary renal hypouricemia is characterized by hypouricemia with hyper-uric acid clearance due to a defect in renal tubular transport. Patients with hereditary renal hypouricemia have a higher risk of exercise-induced acute kidney injury (EAKI) and reduced kidney function. Although the best preventive measure is avoiding exercise, there are many kinds of jobs that require occupational exercise. A 27-year-old male police officer suffered from stage 3 AKI after performing a 20-m multistage shuttle run test. His mother had previously been diagnosed as having renal hypouricemia at another facility. The patient had reported having hypouricemia during a health check at a previous police station, but his serum uric acid concentration was within the normal range at our hospital. After treatment, he recovered from EAKI and exhibited low serum uric acid and hyper-uric acid clearance. Since the patient desired to continue his career requiring strenuous exercise, it was difficult to establish a preventive plan against the recurrence of EAKI. Patients with hereditary renal hypouricemia who must undergo strenuous occupational anaerobic exercise are at higher risk of developing EAKI than other workers. The risks of EAKI among patients with hypouricemia should be considered when undergoing physical occupational training.

Management of a pregnant woman with hypouricemia: a case report

Renal hypouricemia is associated with urinary calculi and severe acute renal failure after exercise. The epidemiology of renal hypouricemia is not yet sufficiently understood, and there is no report of it occurring during pregnancy. We report the case of a pregnant woman with renal hypouricemia. At her first pregnancy, she developed preeclampsia with severe features at the 34th week of gestation. After parturition, she developed acute renal failure and was diagnosed with renal hypouricemia. During the second pregnancy, when she was referred to our hospital, care was taken to ensure adequate hydration by infusion of liquids and water at the time of labour. Consequently, she did not have onset of renal hypouricemia. We suggest that acute renal failure may be avoided in pregnant women with renal hypouricemia by preventing dehydration via drinking enough during pregnancy postpartum period and by infusion during labour.

Atypical anti-glomerular basement membrane disease presenting as macroscopic haematuria, loin pain and acute kidney injury after intensive exercise

We report a 35-year-old man who suffered from recurrent macroscopic haematuria after intensive exercise. One episode was associated with bilateral loin (flank) pain and severe acute kidney injury. His kidney biopsy revealed an atypical anti-glomerular basement membrane (GBM) disease typified by bright linear GBM staining for monotypic immunoglobulin G but without a diffuse crescentic phenotype and no circulating anti-GBM antibody. Outcome was spontaneously favourable. The patient had no recurrence or urine abnormality without running. The original presentation emphasized that exercise could reveal an underlying glomerulopathy.

Distribution and Characteristics of Hypouricemia within the Japanese General Population: A Cross-Sectional Study

Background and objectives: There is insufficient epidemiological knowledge of hypouricemia. In this study, we aimed to describe the distribution and characteristics of Japanese subjects with hypouricemia. Materials and Methods: Data from subjects who underwent routine health checkups from January 2001 to December 2015 were analyzed in this cross-sectional study. A total of 246,923 individuals, which included 111,117 men and 135,806 women, met the study criteria. The participants were divided into quartiles according to their serum uric acid (SUA) levels. We subdivided the subjects with hypouricemia, which was defined as SUA level ≤ 2.0 mg/dL, into two groups and compared their characteristics, including their cardiovascular risks. Results: The hypouricemia rates were 0.46% overall, 0.21% for the men and 0.66% for the women (P < 0.001). The number of the subjects with hypouricemia showed two distributions at SUA levels of 0.4–1.1 mg/dL (lower hypouricemia group), which included a peak at 0.7–0.8 mg/dL, and at SUA levels of 1.4–2.0 mg/dL (higher hypouricemia group). The men in the higher hypouricemia group had lower body mass indexes (BMI) and triglyceride (TG) levels and had higher fasting blood glucose levels than those in the lower hypouricemia group. The women in the higher hypouricemia group were younger; had lower BMI, total protein, TG, total cholesterol and low-density lipoprotein cholesterol levels; and had higher estimated glomerular filtration rates levels compared to those in the lower hypouricemia group. Conclusions: The characteristics of the individuals in the lower and higher hypouricemia groups differed significantly, indicating different pathophysiologies within each group.

Unexpected high plasma xanthine oxidoreductase activity in female subjects with low levels of uric acid

Hypouricemia is a high-risk factor of exercise-induced acute kidney injury (EIAKI) probably through a lack of an antioxidant effect of uric acid. Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the formation of uric acid from hypoxanthine and xanthine, leading to an increase in superoxide and reactive oxygen species. Activation of XOR has been proposed to promote oxidative stress-related tissue injury. We measured plasma XOR activity by a sensitive and accurate assay using a combination of liquid chromatography and triple quadrupole mass spectrometry in subjects with relatively low levels of uric acid (≤4.0 mg/dL) who were recruited from 627 subjects (male/female: 292/335) in the Tanno-Sobetsu Study, a population-based cohort. The numbers of subjects with uric acid ≤4.0 mg/dL, ≤3.0 mg/dL and ≤2.0 mg/dL were 72 (11.5%, male/female: 5/67), 13 (2.1%, all females) and 2 (0.3%, both females), respectively. Plasma XOR activities in 5 male subjects were below the median value of the 292 male subjects. In 12 (17.9%) of the 67 female subjects with uric acid ≤4.0 mg/dL, plasma XOR activities were above the upper quartile value of the 335 female subjects. Eleven of the 12 female subjects with high plasma XOR activity and a low uric acid level had liver dysfunction and/or insulin resistance. In conclusion, unexpected high plasma XOR activities were found in some female subjects with relatively low levels of uric acid. Measurement of plasma XOR activity may help to identify hypouricemic patients with a high risk for EIAKI.

URAT1 and GLUT9 mutations in Spanish patients with renal hypouricemia

BACKGROUND

Renal hypouricemia (RHUC), a rare inherited disorder characterized by impaired uric acid (UA) reabsorption in the proximal tubule, is caused by mutations in SLC22A12 or SLC2A9. Most mutations have been identified in Japanese patients, and only a few have been detected in Europeans.

METHODS

We report clinical, biochemical and genetics findings of fourteen Spanish patients, six Caucasians and eight of Roma ethnia, diagnosed with idiopathic RHUC. Two of the patients presented exercise-induced acute renal failure and another one had several episodes of nephrolithiasis and four of them had progressive deterioration of renal function, while the rest were asymptomatic.

RESULTS

Molecular analysis revealed SLC22A12 mutations in ten of the patients, and SLC2A9 mutations in the other four. A new heterozygous SLC22A12 missense mutation, c.1427C>A (p.A476D), was identified in two affected members of the same family. The rest of the patients presented homozygous, heterozygous or compound heterozygous mutations that have been previously identified in patients with RHUC; SLC22A12 p.T467M and p.L415_G417del, and SLC2A9 p.T125M. Expression studies in Xenopus oocytes revealed that c.1427C>A reduced UA transport but did not alter the location of URAT1 protein on the plasma membrane.

CONCLUSIONS

The biochemical and clinical features of our patients together with the genetic analysis results confirmed the diagnosis of RHUC. This is the first report describing SLC22A12 and SLC2A9 mutations in Spanish patients.

Uric acid, an important screening tool to detect inborn errors of metabolism: a case series

Background

Uric acid is the metabolic end product of purine metabolism in humans. Altered serum and urine uric acid level (both above and below the reference ranges) is an indispensable marker in detecting rare inborn errors of metabolism. We describe different case scenarios of 4 Sri Lankan patients related to abnormal uric acid levels in blood and urine.

Case 1

A one-and-half-year-old boy was investigated for haematuria and a calculus in the bladder. Xanthine crystals were seen in microscopic examination of urine sediment. Low uric acid concentrations in serum and low urinary fractional excretion of uric acid associated with high urinary excretion of xanthine and hypoxanthine were compatible with xanthine oxidase deficiency.

Case 2

An 8-month-old boy presented with intractable seizures, feeding difficulties, screaming episodes, microcephaly, facial dysmorphism and severe neuro developmental delay. Low uric acid level in serum, low fractional excretion of uric acid and radiological findings were consistent with possible molybdenum cofactor deficiency. Diagnosis was confirmed by elevated levels of xanthine, hypoxanthine and sulfocysteine levels in urine.

Case 3

A 3-year-10-month-old boy presented with global developmental delay, failure to thrive, dystonia and self-destructive behaviour. High uric acid levels in serum, increased fractional excretion of uric acid and absent hypoxanthine–guanine phosphoribosyltransferase enzyme level confirmed the diagnosis of Lesch–Nyhan syndrome.

Case 4

A 9-year-old boy was investigated for lower abdominal pain, gross haematuria and right renal calculus. Low uric acid level in serum and increased fractional excretion of uric acid pointed towards hereditary renal hypouricaemia which was confirmed by genetic studies.

Conclusion

Abnormal uric acid level in blood and urine is a valuable tool in screening for clinical conditions related to derangement of the nucleic acid metabolic pathway.

Acute Renal Failure with Severe Loin Pain and Patchy Renal Vasoconstriction in a Patient without Hypouricemia, Provoked by Epileptic Seizure

A 26-year-old Japanese man without hypouricemia and with 3 previous episodes of seizures concurrent with acute kidney injury (AKI) was admitted due to an epileptic seizure, lower back pain and AKI. His creatinine kinase levels were slightly elevated. Patchy renal ischemia on contrast-enhanced computed tomography and persistent residual contrast medium was observed, consistent with acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE). Diffusion-weighted imaging (DWI) demonstrated signal changes in the corresponding area. ALPE should be considered a cause of AKI following seizures. We recommend DWI as an alternative diagnostic modality.

Prevalence and complications of hypouricemia in a general population: A large-scale cross-sectional study in Japan

BACKGROUNDS

Hypouricemia was reported as a risk factor for exercise-induced acute renal injury (EIAKI) and urinary stones. However, the prevalence of kidney diseases among hypouricemic subjects has not been evaluated. This study was conducted to clarify the prevalence of hypouricemia and the association of hypouricemia with kidney diseases by using a large-scale Japanese population data.

METHODS

This study is a retrospective cross-sectional study at the Center for Preventive Medicine, St. Luke's International Hospital, Tokyo, Japan, and Sanin Rousai Hospital, Yonago, Japan. We analyzed the medical records of 90,143 Japanese subjects at the center in St. Luke's International Hospital, Tokyo, and 4,837 subjects in Sanin Rousai Hospital, Yonago, who underwent annual regular health check-up between January 2004 and June 2010. We defined hypouricemia as serum uric acid level of ≤2.0 mg/dL. We checked the medical history of all the study subjects and compared the rates of complications including urinary stones and kidney diseases among those with or without hypouricemia.

RESULTS

The prevalence of hypouricemia was 0.19% in St. Luke's International Hospital, Tokyo, and 0.58% in Sanin Rousai Hospital, Yonago. The prevalence of hypouricemia in women was larger than that in men both in Tokyo (0.31% vs 0.068%, p<0.001) and in Yonago (1.237% vs 0.318%, p<0.001). Among 172 hypouricemic subjects (30 men), the rates of previous urinary stones and kidney diseases (including nephritis/nephrosis) were 1.2% (3.3% men, 0.7% women) and 2.3% (10% men, 0.7% women), respectively. Hypouricemic men had a 9-fold higher rate of previously having kidney diseases compared to non-hypouricemic men (p<0.001). However, the rates of other diseases including urinary stones were not significantly different between the two groups.

CONCLUSIONS

Hypouricemia was associated with a history of kidney disease especially in men.

Rare case of nephrocalcinosis in the distal tubules caused by hereditary renal hypouricaemia 3 months after kidney transplantation

We report a rare case of nephrocalcinosis caused by hereditary renal hypouricaemia 3 months after kidney transplantation. A 41-year-old man who underwent living-related kidney transplantation from his father was admitted to our hospital for a protocol biopsy; he had a serum creatinine (S-Cr) of 1.37 mg/dL and no proteinuria. Histologically, there was no evidence of rejection or calcineurin inhibitor toxicity, although scattered nephrocalcinosis was observed in the distal tubules. Perioperatively, the patient had a serum uric acid (S-UA) of 1.9 mg/dL with a fractional excretion of uric acid (FEUA) of 29% (normal, <10%) and UA clearance of 26.8 mL/min (normal, 7.3-14.7 mL/min) 3 days after kidney transplantation. The donor also had a relatively low S-UA of 2.4 mg/dL and high FEUA of 10.3%. Subsequent DNA direct sequencing followed by restriction fragment length polymorphism revealed that both the recipient's and donor's urate transporter 1 (URAT1) gene had a heterozygous nonsense mutation in exon 5 (C889T). Further, the immunoreactivity of antibodies for the C terminus of URAT1 revealed a partial deletion. De Galantha and von Kossa staining revealed that the nephrocalcinosis was due to urate crystals and calcium stones. Therefore, we diagnosed hereditary renal hypouricaemia. We directed the patient to avoid hard exercise, drink plenty of water, and alkalize the urine. The 1-year follow-up allograft biopsy showed no evidence of nephrocalcinosis in the distal tubules. This is the first report of nephrocalcinosis in the distal tubules as a diagnostic clue to hereditary renal hypouricaemia. We also review the related literature.

Sex-specific Relationship of Serum Uric Acid with All-cause Mortality in Adults with Normal Kidney Function: An Observational Study

OBJECTIVE

To explain the clinical effect of serum uric acid (SUA) levels as a risk factor for mortality, considering exclusion of kidney function.

METHODS

Participants aged over 40 years who underwent health checkups were recruited. Individuals with estimated glomerular filtrations rates < 60 ml/min/1.73 m² and who received laboratory study and colonoscopy on the same day were excluded.

RESULTS

SUA levels were higher in men than in women (5.7 ± 1.2 mg/dl for men and 4.2 ± 0.9 mg/dl for women, p < 0.001). During 12.3 ± 3.6 years of followup, 1402 deaths occurred among 27,490 participants. About 6.9% of men and 3.1% of women died. The overall mortality rate had a U-shaped association with SUA levels, a U-shaped association in men, and no association in women. There was a significant interaction of sex for the SUA-mortality association (p for interaction = 0.049); therefore, survival analysis was conducted by sex. In men, the lower SUA group had a higher mortality rate after adjustment (SUA ≤ 4.0 mg/dl, adjusted HR 1.413, 95% CI 1.158-1.724, p = 0.001) compared with the reference group (SUA 4.1-6.0 mg/dl). A higher SUA contributed to an insignificant increased mortality in men (> 8.0 mg/dl, adjusted HR 1.140, 95% CI 0.794-1.636, p = 0.479). Women failed to show any significant association between SUA and mortality.

CONCLUSION

This study provided novel evidence that SUA-mortality association differed by sex. We demonstrated that a lower SUA was an independent risk factor for all-cause mortality in men with normal kidney function.

Biochemical response to physical exercise in show-jumping horses

The information on the biochemical response of horses submitted to physical exercise by jumping over obstacles is limited and controversial. The purpose of the present study was to monitor the change in activity of muscle enzymes creatine kinase (CK), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as the serum concentrations of triacylglycerols, cholesterol and creatinine in performance horses. Correlations between study parameters were also estimated. Six healthy Hanoverian geldings were submitted to physical exercise similar to a competition consisting of jumping over barriers over four consecutive days. The applied exercise induced increases of biochemical parameters CK, AST, ALT, triacylglycerols, total cholesterol and creatinine within the reference ranges. The changes in these parameters reflected the changes in skeletal muscle and kidney functions as well as alterations in the type of used energy. Negative correlations were established between CK and ALT at 2 hours, and between triacylglycerols and total cholesterol during the entire period of the study. Also, a positive association was established between СK and AST at 24 hours and between total cholesterol and creatinine before exercise, and at 0 and 2 hours post-exercise. The data from the present study could be utilised as guidelines for prevention and early detection of metabolic disturbances in show jumping horses.

A case of xanthinuria type I with a novel mutation in xanthine dehydrogenase

Hereditary hypouricemia is generally caused by renal hypouricemia, an autosomal recessive disorder that is characterized by impaired renal tubular uric acid transport, or by xanthinuria, a rare autosomal recessive disorder caused by a deficiency of xanthine dehydrogenase (XDH; xanthinuria type I) or by a deficiency of both XDH and aldehyde oxidase (xanthinuria type II). In contrast to renal hypouricemia, which sometimes leads to exercise-induced acute kidney injury (EIAKI), xanthinuria has not been associated with this disorder. We report here a case of xanthinuria type I due to a compound heterozygous mutation. A 46-year-old woman was found to have undetectable plasma and urinary levels of uric acid. She had no symptoms and no history of EIAKI. Xanthinuria type I was diagnosed following the allopurinol loading test. Mutation analysis revealed a compound heterozygous mutation [c.305A>G (p.Gln102Arg) and c.2567delC (p.Thr856Lysfs*73)] in the XDH gene. Of these two mutations, the former is novel. The patient did not exhibit EIAKI. However, because xanthinuria is a rare disease, the identification of additional cases is necessary to determine whether this disease is complicated with EIAKI.

Relationship between Serum Uric Acid Levels and Chronic Kidney Disease in a Japanese Cohort with Normal or Mildly Reduced Kidney Function

Background

Some observational studies have shown the relationships between hyperuricemia and chronic kidney disease (CKD); however, the threshold of serum uric acid (SUA) for deterioration of kidney function and the association between SUA and kidney injury by baseline kidney function remains unclear. This study aimed to clarify the relationships between SUA and reduced kidney function.

Methods

We analyzed a historical cohort of male Japanese individuals who underwent medical checkup between 1998 and 2007. Participants with baseline data and who were followed up for at least one year were included and stratified according to baseline kidney function. Kidney function was classified as normal [estimated glomerular filtration rate (eGFR) ≥ 90 ml/min/1.73 m²] or mildly reduced (eGFR 60–89 ml/min/1.73 m²). The outcome measured was kidney impairment defined as a decrease in eGFR to < 60 ml/min/1.73 m². Associations between SUA and risk for outcome and eGFR slopes were assessed.

Results

A total of 41632 subjects with mean age 45.4 years were included. During a mean follow-up of four years, 3186 (7.6%) subjects developed kidney dysfunction. Subjects with SUA ≥ 6.0 mg/dL had a significantly increased risk for kidney impairment compared with subjects with SUA of 4–4.9 mg/dL. SUA threshold levels were different according to baseline kidney function; SUA ≥ 7.0 and ≥ 6.0 mg/dL for normal and mildly reduced kidney function, respectively. Approximately the same trends were observed for eGFR slopes.

Conclusion

In the general population, hyperuricemia appears to be a risk factor for kidney impairment in males. For participants with mild kidney dysfunction, even a slight elevation of SUA can be a risk factor.

Association between hypouricemia and reduced kidney function: a cross-sectional population-based study in Japan

BACKGROUND

Hypouricemia, conventionally defined as a serum uric acid level of ≤2 mg/dl, is considered a biochemical disorder with no clinical significance. However, individuals with renal hypouricemia have a high risk of urolithiasis and exercise-induced acute kidney injury, both of which are risk factors for reduced kidney function.

METHODS

To test the hypothesis that individuals with hypouricemia would be at a higher risk of reduced kidney function, we conducted a population-based cross-sectional study using data from the Specific Health Checkups and Guidance System in Japan. Logistic analysis was used to examine the relationship between hypouricemia and reduced kidney function, defined as estimated glomerular filtration rate <60 ml/min/1.73 m(2).

RESULTS

Among 90,710 men (mean age, 63.8 years) and 136,935 women (63.7 years), 193 (0.2%) and 540 (0.4%) were identified as having hypouricemia, respectively. The prevalence of hypouricemia decreased with age in women (p for trend <0.001), but not in men (p for trend = 0.24). Hypouricemia was associated with reduced kidney function in men (odds ratio, 1.83; 95% confidence interval, 1.23-2.74), but not in women (0.61; 0.43-0.86), relative to the reference category (i.e., serum uric acid levels of 4.1-5.0 mg/dl) after adjusting for age, drinking, smoking, diabetes, hypertension, hypercholesterolemia, obesity, and history of renal failure. Sensitivity analyses stratified by diabetic status yielded similar results.

CONCLUSIONS

This study is the first to provide evidence that hypouricemia is associated with reduced kidney function in men. Further research will be needed to determine the long-term prognosis of individuals with hypouricemia.

Uric acid level has a U-shaped association with loss of kidney function in healthy people: a prospective cohort study

Background

The relationship between hyperuricemia and chronic kidney disease (CKD) has been found in various observational studies. Although hypouricemia is associated with cardiovascular events, it has not been established as a risk factor for CKD. We investigated the relationship between serum uric acid level and the loss of kidney function and incident CKD in healthy people.

Materials and Methods

Healthy people were enrolled in this community-based prospective cohort study, the Saitama Cardiometabolic Disease and Organ Impairment Study, Japan. The analysis was conducted on 4188 subjects followed up for at least 3 years, 3102 for 6 years and 1052 for 9 years. Their data including glomerular filtration rate (eGFR) decline were examined every three years. The outcome event was incident CKD or the decrease in eGFR by more than 25% in three years. Multivariate statistical models were adjusted for the baseline characteristics.

Results

The following data was obtained: mean±SD age, male, 39.6±10.4 years, female 38.4±10.8 years; eGFR, male, 81.9±16.4 ml/min/1.73m2, female, 82.1±17.5 ml/min/1.73m2; serum uric acid level, male, 5.8±1.2 mg/dl, female, 4.1±0.9 mg/dl. Both low and high serum uric acid levels were associated with the outcome and eGFR decline in males (multivariate logistic additional additive models, linear p = 0.0001, spline p = 0.043; generalized additive models, linear p = 0.0001, spline p = 0.012). In subjects with low serum uric acid levels (male, <5 mg/dl; female, <3.6 mg/dl), multivariate linear mixed models showed that low serum uric acid levels were associated with eGFR decline in a time-dependent manner (male, p = 0.0001; female, p = 0.045).

Conclusion

This study showed that low as well as high levels of uric acid are associated with the loss of kidney function. Hypouricemia is a candidate predictor of kidney function decline in healthy people.

Modern diagnostic approach to hereditary xanthinuria

Hereditary xanthinuria (HX) is a rare inherited disorder caused by a deficiency of xanthine dehydrogenase/oxidase (XDH/XO). Missing XDH/XO activity leads to undetectable levels of uric acid excessively replaced by xanthine in serum/urine. The allopurinol loading test has been traditionally used to differentiate between HX types I and II. Final confirmation of HX has been based on the biopsy finding of the absent XDH/XO activity in the small intestine or liver. We present the clinical, biochemical, ultrasound and molecular genetics findings in three new patients with HX and suggest a simple three-step approach to be used for diagnosis, typing and confirmation of HX. In the first step, the diagnosis of HX is determined by extremely low serum/urinary uric acid excessively replaced by xanthine. Second, HX is typed using urinary metabolomics. Finally, the results are confirmed by molecular genetics. We advocate for this safe and non-invasive diagnostic algorithm instead of the traditional allopurinol loading test and intestinal or liver biopsy used in the past.

Acute kidney injury after acute gastroenteritis in an infant with hereditary hypouricemia

Hereditary hypouricemia is a rare disorder characterized by extremely low serum uric acid levels caused by excessive urinary excretion due to an inherited tubular defect in urate handling. Exercise-induced acute kidney injury (AKI) is the main complication of this disorder, though AKI may also be induced by other factors. A 7-month-old boy with hereditary hypouricemia developed AKI associated with severe dehydration caused by rotavirus gastroenteritis. He also showed severe hypernatremia and metabolic acidosis and received continuous renal replacement therapy for 3 days. He showed no signs of hydronephrosis or urolithiasis. However, hypouricemia was noted when his renal function recovered (serum uric acid <0.6 mg/dl). Analysis of the urate transporter 1 gene revealed a homozygous nonsense mutation in exon 4 (c.774G > A, p.W258X). Both parents were heterozygous for the mutation and his younger brother was later determined to have severe hypouricemia (0.6 mg/dl).

CONCLUSION

Uric acid is an essential factor for scavenging oxidative stressors. In this patient, severe dehydration may have directly caused pre-renal AKI, but susceptibility to oxidative stressors under severe dehydration, as well as exercise, may also contribute to AKI. Careful attention should be paid to dehydration, especially in young children, to avoid the development of AKI in patients with hereditary hypouricemia.

Sex differences in serum CK activity but not in glomerular filtration rate after resistance exercise: is there a sex dependent renal adaptative response?

We investigated differences in sex responses in serum CK activity and renal function measured by glomerular filtration rate (GFR) after an exercise session. Twenty-two healthy and trained volunteers (11 males and 11 females) performed 17 resistance exercises with 3 × 12 repetitions in a circuit training fashion. Subjects provided blood samples prior to exercise session, and at 24, 48, and 72 h following exercise sessions for creatine kinase and creatinine. Twenty-four-hour urine samples were collected before and 72 h after the exercise. Estimate (e) GFR was obtained by using the Chronic Kidney Disease Epidemiology Collaboration equation adjusted for males and females. After the exercise session, males showed greater serum CK activity than females (p < 0.02), serum creatinine increased 31.3 % for males and 29.8 % for females, and urinary creatinine decreased on average 5.4 % for males and 0.6 % for females, with no significant differences (p > 0.05) between sex for serum and urinary creatinine. eGFR decreased significantly for males (~10 %) and females (~8 %), but also without a difference between the sexes (p > 0.05). The correlation between CK and eGFR was significant for males (r = -0.794; p = 0.003), and females (r = -0.8875; p < 0.001). A significant negative correlation between CK activity and the eGFR indice of renal function in both males and females was observed. Additionally, the renal function compromise was similar for both sexes, despite males presenting greater exercise-induced skeletal muscle damage when compared to females.