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

Preconditioning by Moderate-Intensity Exercise Prevents Gentamicin-Induced Acute Kidney Injury

A strict correlation among proximal tubule epithelial cell dysfunction, proteinuria, and modulation of the Renin-Angiotensin System and Kalikrein-Kinin System are crucial factors in the pathogenesis of Acute Kidney Injury (AKI). In this study, we investigated the potential protective effect of preconditioning by moderate-intensity aerobic exercise on gentamicin-induced AKI. Male Wistar rats were submitted to a moderate-intensity treadmill exercise protocol for 8 weeks, and then injected with 80 mg/kg/day s.c. gentamicin for 5 consecutive days. Four groups were generated: 1) NT+SAL (control); 2) NT+AKI (non-trained with AKI); 3) T+SAL (trained); and 4) T+AKI (trained with AKI). The NT+AKI group presented: 1) impairment in glomerular function parameters; 2) increased fractional excretion of Na + , K + , and water; 4) proteinuria and increased urinary γ-glutamyl transferase activity (a marker of tubular injury) accompanied by acute tubular necrosis; 5) an increased renal angiotensin-converting enzyme and bradykinin B1 receptor mRNA expression. Interestingly, the preconditioning by moderate-intensity aerobic exercise attenuated all alterations observed in gentamicin-induced AKI (T+AKI group). Taken together, our results show that the preconditioning by moderate-intensity aerobic exercise ameliorates the development of gentamicin-induced AKI. Our findings help to expand the current knowledge regarding the effect of physical exercise on kidneys during physiological and pathological conditions.

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.

Altered Serum Uric Acid Levels in Kidney Disorders

Serum uric acid levels are altered by kidney disorders because the kidneys play a dominant role in uric acid excretion. Here, major kidney disorders which accompany hyperuricemia or hypouricemia, including their pathophysiology, are discussed. Chronic kidney disease (CKD) and hyperuricemia are frequently associated, but recent clinical trials have not supported the pathogenic roles of hyperuricemia in CKD incidence and progression. Diabetes mellitus (DM) is often associated with hyperuricemia, and hyperuricemia may be associated with an increased risk of diabetic kidney disease in patients with type 2 DM. Sodium-glucose cotransporter 2 inhibitors have a uricosuric effect and can relieve hyperuricemia in DM. Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an important hereditary kidney disease, mainly caused by mutations of uromodulin (UMOD) or mucin-1 (MUC-1). Hyperuricemia and gout are the major clinical manifestations of ADTKD-UMOD and ADTKD-MUC1. Renal hypouricemia is caused by URAT1 or GLUT9 loss-of-function mutations and renders patients susceptible to exercise-induced acute kidney injury, probably because of excessive urinary uric acid excretion. Hypouricemia derived from renal uric acid wasting is a component of Fanconi syndrome, which can be hereditary or acquired. During treatment for human immunodeficiency virus, hepatitis B or cytomegalovirus, tenofovir, adefovir, and cidofovir may cause drug-induced renal Fanconi syndrome. In coronavirus disease 2019, hypouricemia due to proximal tubular injury is related to disease severity, including respiratory failure. Finally, serum uric acid and the fractional excretion of uric acid are indicative of plasma volume status; hyperuricemia caused by the enhanced uric acid reabsorption can be induced by volume depletion, and hypouricemia caused by an increased fractional excretion of uric acid is the characteristic finding in syndromes of inappropriate anti-diuresis, cerebral/renal salt wasting, and thiazide-induced hyponatremia. Molecular mechanisms by which uric acid transport is dysregulated in volume or water balance disorders need to be investigated.

Renal hypouricemia in a recipient of living-donor kidney transplantation: a case report and literature review

Hypouricemia in kidney transplant (KT) recipients is rare since they usually have subnormal kidney function which raises serum uric acid level. Recently, interests in pathogenesis of hypouricemia have been increasing due to the understanding of the role of uric acid transporter in renal hypouricemia (RHUC). We herein report the case of RHUC consequently developed in a KT recipient from a living donor with RHUC diagnosed by the detailed urinary and genetic test. A 73-year-old Japanese man underwent KT, and the donor was his wife who had hypouricemia [serum uric acid (S-UA) 0.6 mg/dL]. Nine months after KT, the recipient's S-UA was low (1.5 mg/dL) with serum creatinine (S-Cr) of 1.56 mg/dL, and fractional excretion of UA (FEUA) was high (59.7%; normal < 10%), indicating RHUC. Regarding the donor's information, S-Cr, S-UA, and FEUA were 0.95 mg/dL, 1.0 mg/dL, and 54.5%, respectively. To investigate further on the pathogenesis of RHUC in both the recipient and the donor, we performed genetic tests. The donor had a homozygous mutation of W258X in the SLC22A12 gene and the recipient had a wild type of W258X. Finally, we reviewed the previous literature on RHUC among KT recipients and discussed the strategy of follow-up for these patients.

Xanthine Oxidoreductase Inhibitors Suppress the Onset of Exercise-Induced AKI in High HPRT Activity Urat1-Uox Double Knockout Mice

BACKGROUND

Hereditary renal hypouricemia type 1 (RHUC1) is caused by URAT1/SLC22A12 dysfunction, resulting in urolithiasis and exercise-induced AKI (EIAKI). However, because there is no useful experimental RHUC1 animal model, the precise pathophysiologic mechanisms underlying EIAKI have yet to be elucidated. We established a high HPRT activity Urat1-Uox double knockout (DKO) mouse as a novel RHUC1 animal model for investigating the cause of EIAKI and the potential therapeutic effect of xanthine oxidoreductase inhibitors (XOIs).

METHODS

The novel Urat1-Uox DKO mice were used in a forced swimming test as loading exercise to explore the onset mechanism of EIAKI and evaluate related purine metabolism and renal injury parameters.

RESULTS

Urat1-Uox DKO mice had uricosuric effects and elevated levels of plasma creatinine and BUN as renal injury markers, and decreased creatinine clearance observed in a forced swimming test. In addition, Urat1-Uox DKO mice had increased NLRP3 inflammasome activity and downregulated levels of Na⁺-K⁺-ATPase protein in the kidney, as Western blot analysis showed. Finally, we demonstrated that topiroxostat and allopurinol, XOIs, improved renal injury and functional parameters of EIAKI.

CONCLUSIONS

Urat1-Uox DKO mice are a useful experimental animal model for human RHUC1. The pathogenic mechanism of EIAKI was found to be due to increased levels of IL-1β via NLRP3 inflammasome signaling and Na⁺-K⁺-ATPase dysfunction associated with excessive urinary urate excretion. In addition, XOIs appear to be a promising therapeutic agent for the treatment of EIAKI.

Uric Acid in Inflammation and the Pathogenesis of Atherosclerosis

Hyperuricemia is a common metabolic syndrome. Elevated uric acid levels are risk factors for gout, hypertension, and chronic kidney diseases. Furthermore, various epidemiological studies have also demonstrated an association between cardiovascular risks and hyperuricemia. In hyperuricemia, reactive oxygen species (ROS) are produced simultaneously with the formation of uric acid by xanthine oxidases. Intracellular uric acid has also been reported to promote the production of ROS. The ROS and the intracellular uric acid itself regulate several intracellular signaling pathways, and alterations in these pathways may result in the development of atherosclerotic lesions. In this review, we describe the effect of uric acid on various molecular signals and the potential mechanisms of atherosclerosis development in hyperuricemia. Furthermore, we discuss the efficacy of treatments for hyperuricemia to protect against the development of atherosclerosis.

Mutation in the SLC2A9 Gene: A New Family with Familial Renal Hypouricemia Type 2

Familial renal hypouricemia is a rare genetic disorder characterized by a defect in renal tubular urate reabsorption. Some patients present with exercise-induced acute kidney injury and nephrolithiasis. Type II is caused by mutations in the SLC2A9 gene. Here, we report the case of a young patient who developed acute kidney injury after exercise secondary to familial renal hypouricemia type II. The same mutation was found in other asymptomatic members of his family. We review the medical literature on this condition. This case highlights the importance of considering uric acid disorders in the work-up of acute kidney injury after exercise.

Urate Transporters in the Kidney: What Clinicians Need to Know

Urate is produced in the liver by the degradation of purines from the diet and nucleotide turnover and excreted by the kidney and gut. The kidney is the major route of urate removal and has a pivotal role in the regulation of urate homeostasis. Approximately 10% of the glomerular filtered urate is excreted in the urine, and the remainder is reabsorbed by the proximal tubule. However, the transport of urate in the proximal tubule is bidirectional: reabsorption and secretion. Thus, an increase in reabsorption or a decrease in secretion may induce hyperuricemia. In contrast, a decrease in reabsorption or an increase in secretion may result in hyperuricosuria. In the proximal tubule, urate reabsorption is mainly mediated by apical URAT1 (SLC22A12) and basolateral GLUT9 (SLC2A9) transporter. OAT4 (SLC22A11) also acts in urate reabsorption in the apical membrane, and its polymorphism is associated with the risk of hyperuricemia. Renal hypouricemia is caused by SLC22A12 or SLC2A9 loss-of-function mutations, and it may be complicated by exercise-induced acute kidney injury. URAT1 and GLUT9 are also drug targets for uricosuric agents. Sodium-glucose cotransporter inhibitors may induce hyperuricosuria by inhibiting GLUT9b located in the apical plasma membrane. Urate secretion is mediated by basolateral OAT1 (SLC22A6) and OAT3 (SLC22A8) and apical ATP-binding cassette super-family G member 2 (ABCG2), NPT1 (SLC17A1), and NPT4 (SLC17A3) transporter in the proximal tubule. NPT1 and NPT4 may be key players in renal urate secretion in humans, and deletion of SLC22A6 and SLC22A8 in mice leads to decreased urate excretion. Dysfunctional variants of ABCG2 inhibit urate secretion from the gut and kidney and may cause gout. In summary, the net result of urate transport in the proximal tubule is determined by the dominance of transporters between reabsorption (URAT1, OAT4, and GLUT9) and secretion (ABCG2, NPT1, NPT4, OAT1, and OAT3).

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.

Effects of uric acid dysregulation on the kidney

Recently, research has redirected its interests in uric acid (UA) from gout, an inflammatory disease in joints, to groups of closely interrelated pathologies associated with cardiovascular and kidney dysfunction. Many epidemiological, clinical, and experimental studies have shown that UA may play a role in the pathophysiology of the cardiorenal syndrome continuum; however, it is still unclear if it is a risk factor or a causal role. Hyperuricemia has been well studied in the past two decades, revealing mechanistic insights into UA homeostasis. Likewise, some epidemiological and experimental evidence suggests that hypouricemia can lead to cardiorenal pathologies. The goal of this review is to highlight why studying both hyperuricemia and hypouricemia is warranted as well as to summarize the relevance of UA to kidney function.