Successful treatment with hydrochlorothiazide and amiloride in an infant with congenital nephrogenic diabetes insipidus

EGF Receptor Inhibition by Erlotinib Increases Aquaporin 2-Mediated Renal Water Reabsorption

Nephrogenic diabetes insipidus (NDI) is caused by impairment of vasopressin (VP) receptor type 2 signaling. Because potential therapies for NDI that target the canonical VP/cAMP/protein kinase A pathway have so far proven ineffective, alternative strategies for modulating aquaporin 2 (AQP2) trafficking have been sought. Successful identification of compounds by our high-throughput chemical screening assay prompted us to determine whether EGF receptor (EGFR) inhibitors stimulate AQP2 trafficking and reduce urine output. Erlotinib, a selective EGFR inhibitor, enhanced AQP2 apical membrane expression in collecting duct principal cells and reduced urine volume by 45% after 5 days of treatment in mice with lithium-induced NDI. Similar to VP, erlotinib increased exocytosis and decreased endocytosis in LLC-PK1 cells, resulting in a significant increase in AQP2 membrane accumulation. Erlotinib increased phosphorylation of AQP2 at Ser-256 and Ser-269 and decreased phosphorylation at Ser-261 in a dose-dependent manner. However, unlike VP, the effect of erlotinib was independent of cAMP, cGMP, and protein kinase A. Conversely, EGF reduced VP-induced AQP2 Ser-256 phosphorylation, suggesting crosstalk between VP and EGF in AQP2 trafficking and a role of EGF in water homeostasis. These results reveal a novel pathway that contributes to the regulation of AQP2-mediated water reabsorption and suggest new potential therapeutic strategies for NDI treatment.

Molecular basis and clinical features of nephrogenic diabetes insipidus

Maintenance of water and electrolyte homeostasis is central to mammalian survival and, therefore, under stringent hormonal control. Water homeostasis is achieved by balancing fluid intake with water excretion, governed by the antidiuretic action of arginine vasopressin. Arginine vasopressin stimulation of renal V₂ vasopressin receptors in the basolateral membrane of principal cells induces aquaporin-2-mediated water reabsorption in the kidney. The importance of this system is apparent when mutations inactivate V₂ vasopressin receptors and aquaporin-2 and cause the clinical phenotype of nephrogenic diabetes insipidus. To date, over 190 mutations in the V₂ vasopressin receptors gene (AVPR2) and approximately 38 mutations in the aquaporin-2 gene have been identified in patients with inherited nephrogenic diabetes insipidus. Extensive in vitro expression and mutagenesis studies of V₂ vasopressin receptors and aquaporin-2 have provided detailed insights into the molecular mechanisms of G-protein-coupled receptor and water channel dysfunction per se. Targeted deletions of AVPR2 and AQP2 in mice have extended the knowledge of nephrogenic diabetes insipidus pathophysiology and have stimulated testing of old and new ideas to therapeutically restore normal kidney function in animal models and patients with this disease. In this review, we summarize the current knowledge relevant to understand the molecular basis of inherited nephrogenic diabetes insipidus forms and the rationales for the current pharmacological treatment of patients with this illness.

Diabetes insipidus in children: pathophysiology, diagnosis and management

In diabetes insipidus, the amount of water ingested and the quantity and concentration of urine produced needs to be carefully regulated if fluid volume and osmolality are to be maintained within the normal range. One of the principal mechanisms controlling urine output is vasopressin which is released from the posterior pituitary gland and enhances water reabsorption from the renal collecting duct. In diabetes insipidus, the excessive production of dilute urine, and the causes of this clinical picture can be divided into three main groups: the first is primary polydipsia where the amount of fluid ingested is inappropriately large; the second group is cranial diabetes insipidus where the production of vasopressin is abnormally low; and, the third group is nephrogenic diabetes insipidus where the kidney response to vasopressin is impaired. The history and examination may suggest an underlying explanation for diabetes insipidus but a range of baseline and more extensive investigations may be required before a diagnosis can be reached. These investigations are not without risk, and the results need to be interpreted carefully because children do not always segregate neatly into a particular diagnostic category on the basis of one test alone. Children with cranial diabetes insipidus typically respond to arginine vasopressin or its manufactured analogue, desmopressin, with an increase in urine osmolality and an associated reduction in urine output. Such children usually require neuroimaging to look for evidence of evolving CNS pathology, such as an intracranial tumour. Vasopressin "replacement" with desmopressin is the treatment of choice in patients with cranial diabetes insipidus although extreme caution is required when treating babies or small children because of the danger of fluid overload. Abnormal production of other pituitary hormones in children with CNS disease can also influence fluid balance. Nephrogenic diabetes insipidus can be due to abnormal electrolyte concentrations, therefore these should be measured as part of the initial assessment. In a small number of children the defect is a primary abnormality of the vasopressin receptor or one of the water channel proteins (aquaporins) involved in water transport. The treatment of these patients is difficult and typically involves therapy with a diuretic such as chlorothiazide, as well as indomethacin. These agents enhance urine osmolality by their effect on circulating volume and renal solute and water handling. The fluid intake of most young children with primary polydipsia can be safely reduced to a more appropriate level.

Treatment of nephrogenic diabetes insipidus with hydrochlorothiazide and amiloride

Nephrogenic diabetes insipidus (NDI) is characterised by the inability of the kidney to concentrate urine in response to arginine vasopressin. The consequences are severe polyuria and polydipsia, often associated with hypertonic dehydration. Intracerebral calcification, seizures, psychosomatic retardation, hydronephrosis, and hydroureters are its sequelae. In this study, four children with NDI were treated with 3 mg/kg/day hydrochlorothiazide and 0.3 mg/kg/day amiloride orally three times a day for up to five years. While undergoing treatment, none of the patients had signs of dehydration or electrolyte imbalance, all showed normal body growth, and there was no evidence of cerebral calcification or seizures. All but one had normal psychomotor development and normal sonography of the urinary tract. However, normal fluid balance was not attainable (fluid intake, 3.8-7.7 l/m2/day; urine output, 2.2-7.4 l/m2/day). The treatment was well tolerated and no side effects could be detected. Prolonged treatment with hydrochlorothiazide/amiloride appears to be more effective and better tolerated than just hydrochlorothiazide. Its efficacy appears to be similar to that of hydrochlorothiazide/indomethacin but without their severe side effects.