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

Co-occurrence of exercise-induced acute kidney injury and rhabdomyolysis in a holding cell at a police station: a case report

We present a rare case of a patient with co-occurring exercise-induced acute kidney injury (AKI) and rhabdomyolysis. A 67-year-old man was referred to our department with AKI. Five days before referral, the patient had sudden-onset loin pain while banging and kicking on a door in a holding cell at a police station. Diffusion-weighted magnetic resonance imaging showed wedge-shaped areas of signal hyperintensity in both kidneys. Serum and urinary myoglobin levels were mildly elevated. Kidney biopsy showed cellular injury of the tubular epithelial cells and myoglobin casts in the tubules. The patient was diagnosed with exercise-induced AKI and mild rhabdomyolysis and was treated conservatively. His kidney function improved gradually with no need for hemodialysis. This case report exhibits a unique presentation of the co-occurrence of exercise-induced AKI and rhabdomyolysis after intense anaerobic and aerobic exercise. To the best of our knowledge, this is the first report to pathologically demonstrate co-occurring exercise-induced AKI and rhabdomyolysis.

Dysuricemia

Gout results from elevated serum urate (SU) levels, or hyperuricemia, and is a globally widespread and increasingly burdensome disease. Recent studies have illuminated the pathophysiology of gout/hyperuricemia and its epidemiology, diagnosis, treatment, and complications. The genetic involvement of urate transporters and enzymes is also proven. URAT1, a molecular therapeutic target for gout/hyperuricemia, was initially derived from research into hereditary renal hypouricemia (RHUC). RHUC is often accompanied by complications such as exercise-induced acute kidney injury, which indicates the key physiological role of uric acid. Several studies have also revealed its physiological role as both an anti-oxidant and a pro-oxidant, acting as both a scavenger and a generator of reactive oxygen species (ROSs). These discoveries have prompted research interest in SU and xanthine oxidoreductase (XOR), an enzyme that produces both urate and ROSs, as status or progression biomarkers of chronic kidney disease and cardiovascular disease. The notion of "the lower, the better" is therefore incorrect; a better understanding of uric acid handling and metabolism/transport comes from an awareness that excessively high and low levels both cause problems. We summarize here the current body of evidence, demonstrate that uric acid is much more than a metabolic waste product, and finally propose the novel disease concept of "dysuricemia" on the path toward "normouricemia", or optimal SU level, to take advantage of the dual roles of uric acid. Our proposal should help to interpret the spectrum from hypouricemia to hyperuricemia/gout as a single disease category.