Pseudohypoaldosteronism type II is a salt-sensitive form of hypertension with hyperkalemia in humans caused by mutations in the with-no-lysine kinase 4 (WNK4). Several studies have shown that WNK4 modulates the activity of the renal Na + Cl − cotransporter, NCC. Because the renal consequences of WNK4 carrying pseudoaldosteronism type II mutations resemble the response to intravascular volume depletion (promotion of salt reabsorption without K + secretion), a condition that is associated with high angiotensin II (AngII) levels, it has been proposed that AngII signaling might affect WNK4 modulation of the NCC. In Xenopus laevis oocytes, WNK4 is required for modulation of NCC activity by AngII. To demonstrate that WNK4 is required in the AngII-mediated regulation of NCC in vivo, we used a total WNK4-knockout mouse strain (WNK4 −/− ). WNK4 mRNA and protein expression were absent in WNK4 −/− mice, which exhibited a mild Gitelman-like syndrome, with normal blood pressure, increased plasma renin activity, and reduced NCC expression and phosphorylation at T-58. Immunohistochemistry revealed normal morphology of the distal convoluted tubule with reduced NCC expression. Low-salt diet or infusion of AngII for 4 d induced phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and of NCC at S-383 and T-58, respectively, in WNK4 +/+ but not WNK4 −/− mice. Thus, the absence of WNK4 in vivo precludes NCC and SPAK phosphorylation promoted by a low-salt diet or AngII infusion, suggesting that AngII action on the NCC occurs via a WNK4-SPAK-dependent signaling pathway. Additionally, stimulation of aldosterone secretion by AngII, but not by a high-K + diet, was impaired in WNK4 −/− mice. distal tubule | diuretics | thiazide | renin-angiotensin-aldosterone system

Our data show that aldosterone plays an important role as a mediator of renal injury induced by CsA. Thus, mineralocorticoid receptor blockade may be a potential strategy to prevent CsA nephrotoxicity.

Renal ischemia and reperfusion (I/R) injury is the major cause of acute renal failure and may also be involved in the development and progression of some forms of chronic kidney disease. We previously showed that a mineralocorticoid receptor (MR) blockade prevents renal vasoconstriction induced by cyclosporine that leads to acute and chronic renal failure (Feria I, Pichardo I, Juarez P, Ramirez V, Gonzalez MA, Uribe N, Garcia-Torres R, Lopez-Casillas F, Gamba G, Bobadilla NA. Kidney Int 63: 43-52, 2003; Perez-Rojas JM, Derive S, Blanco JA, Cruz C, Martinez de la Maza L, Gamba G, Bobadilla NA. Am J Physiol Renal Physiol 289: F1020-F1030, 2005). Thus we investigated whether spironolactone administration prevents the functional and structural damage induced by renal ischemia-reperfusion (I/R). Five groups were studied: sham-operated animals, rats that underwent 20 min of ischemia and 24 h of reperfusion, and three groups that received spironolactone 1, 2, or 3 days before I/R, respectively. Renal I/R produced significant renal dysfunction and tubular damage. Spironolactone administration completely prevented a decrease in renal blood flow, the development of acute renal failure, and tubular apoptosis. The protection conferred by spironolactone was characterized by decreasing oxidative stress, as evidenced by a reduction in kidney lipoperoxidation, increasing expression of antioxidant enzymes, and restoration of urinary NO(2)/NO(3) excretion. Endothelial nitric oxide synthase expression was upregulated by a mineralocorticoid receptor blockade in I/R groups; in addition, an increase in activating phosphorylation of this enzyme at residue S1177 and a decrease in inactivating phosphorylation at T497 were observed. In conclusion, our study shows that spironolactone administration prevents the renal injury induced by I/R, suggesting that aldosterone plays a central role in this model of renal injury.

Acute kidney injury (AKI) has been recognized as a risk factor for the development of chronic kidney disease (CKD). Aldosterone has a critical role in promoting renal injury induced by ischemia. Here, we evaluated whether spironolactone administered before or after AKI caused by ischemia protects against CKD. In the first set of experiments, Wistar rats underwent a sham operation without or with prior spironolactone treatment, or underwent 45 minutes of bilateral renal ischemia without or with spironolactone treatment before ischemia and assessed over 270 days. The second set of rats received low (20 mg/kg) or high (80 mg/kg) doses of spironolactone at three different times after the sham operation or bilateral renal ischemia and were assessed after 90 days. Untreated animals developed CKD following ischemia-induced AKI as characterized by a progressive increase in proteinuria, renal dysfunction, podocyte injury, glomerular hypertrophy, and focal sclerosis. This was associated with increased oxidative stress, an upregulation of tumor growth factor (TGF)-β, followed by upregulation of the TGF-β downstream effectors phospho-Smad3, collagen I, fibronectin, and proinflammatory cytokines. Treatment with spironolactone either before or after ischemia prevented subsequent CKD by avoiding the activation of fibrotic and inflammatory pathways. Thus, spironolactone may be a promising treatment for the prevention of AKI-induced CKD.

Recent studies from our laboratory have shown that the mineralocorticoid receptor (MR) blockade with spironolactone (Sp) prevented renal dysfunction and reduced renal injury in both acute and chronic cyclosporine (CsA) nephrotoxicity. This study was designed to evaluate whether Sp administration reduces functional and structural renal damage associated in the setting of preexisting chronic CsA nephrotoxicity. Twenty eight male Wistar rats were fed a low-sodium diet. Fourteen received vehicle (V) and the others were treated with CsA (15 mg/kg sc). After 18 days one half of each group received Sp (20 mg/kg po) for the subsequent 18 days. Creatinine clearance, arteriolopathy, tubulointerstitial fibrosis, arteriolar thickening, glomerular diameter, apoptosis index and TGF-beta, procaspase-3, and kidney injury molecule 1 (Kim-1) mRNA levels as well as Kim-1 shedding in urine were evaluated. Sp reduced the progression of renal dysfunction and tubulointerstitial fibrosis in preexisting chronic CsA nephrotoxicity. There was a significant reduction of arteriolar thickening in the CsA+Sp group that was associated with greater glomerular diameter and reduction of apoptosis index. These renoprotective effects were associated with reduction of TGF-beta, procaspase-3, and Kim-1 mRNA levels as well as Kim-1 shedding into the urine. In conclusion, MR blockade with Sp prevented the progression of renal injury in preexisting chronic CsA nephropathy. These results suggest that Sp may reduce CsA-induced established nephrotoxicity in patients.