Effect of vasopressin on uric acid excretion: evidence for distal nephron reabsorption of urate in man

Mangiferin Ameliorates Hyperuricemic Nephropathy Which Is Associated With Downregulation of AQP2 and Increased Urinary Uric Acid Excretion

Hyperuricemia is characterized by abnormally high level of circulating uric acid in the blood and is associated with increased risk of kidney injury. The pathophysiological mechanisms leading to hyperuricemic nephropathy (HN) involve oxidative stress, endothelial dysfunction, inflammation, and fibrosis. Mangiferin is a bioactive C-glucoside xanthone, which has been exerting anti-inflammatory, anti-fibrotic, and antioxidative effects in many diseases. This study aimed to evaluate the effect of mangiferin treatment in HN. In a mouse model of HN, we observed lower circulating urate levels and ameliorated renal dysfunction with mangiferin treatment, which was associated with reduced renal inflammation and fibrosis. We next investigated the mechanism of urate lowering effect of mangiferin. Metabolic cage experiment showed that mangiferin-administrated mice excreted significantly more urinary uric acid due to elevated urine output, but no marked change in urine uric acid concentration. Expressions of water channels and urate transporters were further assessed by western blot. Renal AQP2 expression was decreased, yet urate transporters URAT1, GLUT9, and OAT1 expressions were not affected by mangiferin in HN mice. Moreover, mangiferin treatment also normalized xanthine oxidase and SOD activity in HN mice, which would decrease uric acid synthesis and improve oxidative stress, respectively. Therefore, our results reveal a novel mechanism whereby mangiferin can reduce serum uric acid levels by promoting AQP2-related urinary uric acid excretion. This study suggested that mangiferin could be a multi-target therapeutic candidate to prevent HN via mechanisms that involve increased excretion and decreased production of uric acid and modulation of inflammatory, fibrotic, and oxidative pathways.

Juvenile-onset gout and adipsic diabetes insipidus: A case report and literature review

The prevalence of juvenile-onset gout has been increasing. Hereditary factors and secondary diseases should be considered in these patients. Adipsic diabetes insipidus (ADI) is characterized by arginine vasopressin (AVP) deficiency, which results in hypotonic polyuria, and dysfunction of thirst osmoreceptors, which results in failure to generate a thirst sensation in response to hypernatremia. We herein report a case of a boy with gouty arthritis, refractory hyperuricemia, prominent hypernatremia, a high creatinine concentration, and a history of surgery for a hypothalamic hamartoma. The patient was diagnosed with central diabetes insipidus after endocrine evaluation. Because he never had symptoms of thirst, the final diagnosis was corrected to ADI. This is the first report of gout due to chronic ADI in an adolescent. Volume contraction due to ADI might be one cause of hyperuricemia and renal impairment in such patients. Moreover, AVP deficiency might directly lead to low urate clearance due to the lack of vasopressin receptor 1 stimulation. Lack of polydipsia and polyuria may delay the diagnosis of ADI and lead to severe complications of a chronic hyperosmolar status. Sufficient and effective establishment of normovolemia is critical for these patients.

Metabolic and Kidney Diseases in the Setting of Climate Change, Water Shortage, and Survival Factors

Climate change (global warming) is leading to an increase in heat extremes and coupled with increasing water shortage, provides a perfect storm for a new era of environmental crises and potentially, new diseases. We use a comparative physiologic approach to show that one of the primary mechanisms by which animals protect themselves against water shortage is to increase fat mass as a means for providing metabolic water. Strong evidence suggests that certain hormones (vasopressin), foods (fructose), and metabolic products (uric acid) function as survival signals to help reduce water loss and store fat (which also provides a source of metabolic water). These mechanisms are intricately linked with each other and stimulated by dehydration and hyperosmolarity. Although these mechanisms were protective in the setting of low sugar and low salt intake in our past, today, the combination of diets high in fructose and salty foods, increasing temperatures, and decreasing available water places these survival signals in overdrive and may be accelerating the obesity and diabetes epidemics. The recent discovery of multiple epidemics of CKD occurring in agricultural workers in hot and humid environments may represent harbingers of the detrimental consequences of the combination of climate change and overactivation of survival pathways.