Lithium-induced nephrogenic diabetes insipidus: New clinical and experimental findings

Lithium (Li+) salts are widely used to treat bipolar mood disorders. Recent trials suggest a potential efficacy also in the treatment of amyotrophic lateral sclerosis and Alzheimer's disease. Li+ is freely filtered by the glomerulus and mainly reabsorbed in the proximal convoluted tubule. Reabsorption in the distal nephron becomes significant under sodium-restricted conditions. Nevertheless, the distal nephron is greatly affected by Li+ even under normal sodium intake. Polyuria, renal tubular acidosis and finally chronic renal failure are the most frequent adverse effects. The occurrence of an overt nephrogenic diabetes insipidus (NDI) limits Li+ usage and imposes suspension. The molecular mechanisms of Li+-related urinary concentration defect involve a dysregulation of the aquaporin system in principal cells of the collecting duct. ENaC is crucial as the entry route for intracellular Li+ accumulation. The basolateral exit route is not clearly identified, but some evidence suggests Na+/H+ exchanger 1 (NHE1) as a potential candidate. Li+ promotes polyuria mainly counteracting the intracellular vasopressin signaling. An additional role of the inner medullary interstitial cells and PGE-2 pathway has to be considered. The GSK3β cascade is also regulated by Li+. GSK3β inhibition could lead not only to the polyuria, but also to the Li+-dependent proliferative effect on principal cells. Cellular reorganization of the collecting duct and microcysts are the main pathological findings during Li+ treatment. Their relationship with the urinary concentration defect and an eventual Li+-induced ciliopathy has to been investigated. Li+-induced NDI has been a matter of investigation since the early 1970s. This manuscript reports the latest clinical and experimental findings in combination with the older fundamental results

Effects of medium hypertonicity on water permeability in the mammalian rectum: ultrastructural and molecular correlates

Minute-by-minute net water fluxes (JW) were measured across the isolated rectal epithelium in rats and rabbits. Five minutes after a serosal (but not mucosal) hypertonic challenge (plus 200 mosmol/l) a significant increase in the basal JW was recorded in both species [ΔJW, μl min-1 cm-2: 0.40±0.06 (rats); 0.45±0.10 (rabbits)]. At the same time, most epithelial cells shrank markedly while the intercellular spaces were wide open (electron microscopy studies). In freeze-fracture studies multi-strand tight-junction structures (only slightly modified by serosal hypertonicity in rabbits) were observed in control conditions. No structural changes were observed after mucosal hypertonicity (both in rats and rabbits). Immunohistochemical studies showed the expression of aquaporin 3 (AQP3) at the basolateral membrane of epithelial cells in the rat. A first conclusion is that the epithelium of the mammalian rectum is a highly polarized, aquaporin-3-containing, water permeability structure. The JW increase induced by serosal hypertonicity was sensitive to mercurial agents in both species and no changes in unidirectional [14C]mannitol fluxes (P(S)) or transepithelial resistance (R(T)) were observed during this JW increase. These observations suggest a transcellular route for the osmotically induced increase in water fluxes. In the rabbit rectum the initial JW response, associated with serosal hypertonicity, was a transient one. It was followed by a second, slow and HgCl2-sensitive JW increase (a transient peak in paracellular mannitol permeability was also observed). A second conclusion is that serosal hypertonicy induces an increase in transcellular water permeability in both rat and rabbit rectum.Fil: Kierbel, Arlinet. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; ArgentinaFil: Capurro, Claudia Graciela. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Pisam, Monique. Inserm; FranciaFil: Gobin, Renée. Inserm; FranciaFil: Mønster Christensen, Birgitte. Inserm; FranciaFil: Nielsen, Soren. Inserm; FranciaFil: Parisi, Mario Nestor. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentin

αENaC-Mediated Lithium Absorption Promotes Nephrogenic Diabetes Insipidus

Lithium-induced nephrogenic diabetes insipidus (NDI) is accompanied by polyuria, downregulation of aquaporin 2 (AQP2), and cellular remodeling of the collecting duct (CD). The amiloride-sensitive epithelial sodium channel (ENaC) is a likely candidate for lithium entry. Here, we subjected transgenic mice lacking αENaC specifically in the CD (knockout [KO] mice) and littermate controls to chronic lithium treatment. In contrast to control mice, KO mice did not markedly increase their water intake. Furthermore, KO mice did not demonstrate the polyuria and reduction in urine osmolality induced by lithium treatment in the control mice. Lithium treatment reduced AQP2 protein levels in the cortex/outer medulla and inner medulla (IM) of control mice but only partially reduced AQP2 levels in the IM of KO mice. Furthermore, lithium induced expression of H+-ATPase in the IM of control mice but not KO mice. In conclusion, the absence of functional ENaC in the CD protects mice from lithium-induced NDI. These data support the hypothesis that ENaC-mediated lithium entry into the CD principal cells contributes to the pathogenesis of lithium-induced NDI

Identification of Acer2 as a First Susceptibility Gene for Lithium-Induced Nephrogenic Diabetes Insipidus in Mice

International audienceBackground: Lithium, mainstay treatment for bipolar disorder, causes nephrogenic diabetes insipidus and hypercalcemia in about 20% and 10% of patients, respectively, and may lead to acidosis. These adverse effects develop in only a subset of patients treated with lithium, suggesting genetic factors play a role.Methods: To identify susceptibility genes for lithium-induced adverse effects, we performed a genome-wide association study in mice, which develop such effects faster than humans. On day 8 and 10 after assigning female mice from 29 different inbred strains to normal chow or lithium diet (40 mmol/kg), we housed the animals for 48 hours in metabolic cages for urine collection. We also collected blood samples.Results: In 17 strains, lithium treatment significantly elevated urine production, whereas the other 12 strains were not affected. Increased urine production strongly correlated with lower urine osmolality and elevated water intake. Lithium caused acidosis only in one mouse strain, whereas hypercalcemia was found in four strains. Lithium effects on blood pH or ionized calcium did not correlate with effects on urine production. Using genome-wide association analyses, we identified eight gene-containing loci, including a locus containing Acer2, which encodes a ceramidase and is specifically expressed in the collecting duct. Knockout of Acer2 led to increased susceptibility for lithium-induced diabetes insipidus development.Conclusions: We demonstrate that genome-wide association studies in mice can be used successfully to identify susceptibility genes for development of lithium-induced adverse effects. We identified Acer2 as a first susceptibility gene for lithium-induced diabetes insipidus in mice

Sodium and potassium balance depends on αENaC expression in connecting tubule.

Mutations in α, β, or γ subunits of the epithelial sodium channel (ENaC) can downregulate ENaC activity and cause a severe salt-losing syndrome with hyperkalemia and metabolic acidosis, designated pseudohypoaldosteronism type 1 in humans. In contrast, mice with selective inactivation of αENaC in the collecting duct (CD) maintain sodium and potassium balance, suggesting that the late distal convoluted tubule (DCT2) and/or the connecting tubule (CNT) participates in sodium homeostasis. To investigate the relative importance of ENaC-mediated sodium absorption in the CNT, we used Cre-lox technology to generate mice lacking αENaC in the aquaporin 2-expressing CNT and CD. Western blot analysis of microdissected cortical CD (CCD) and CNT revealed absence of αENaC in the CCD and weak αENaC expression in the CNT. These mice exhibited a significantly higher urinary sodium excretion, a lower urine osmolality, and an increased urine volume compared with control mice. Furthermore, serum sodium was lower and potassium levels were higher in the genetically modified mice. With dietary sodium restriction, these mice experienced significant weight loss, increased urinary sodium excretion, and hyperkalemia. Plasma aldosterone levels were significantly elevated under both standard and sodium-restricted diets. In summary, αENaC expression within the CNT/CD is crucial for sodium and potassium homeostasis and causes signs and symptoms of pseudohypoaldosteronism type 1 if missing