Activation of tolvaptan-responsive T-cell clones with the structurally-related mozavaptan.

Tolvaptan is an effective drug for the treatment of autosomal dominant polycystic kidney disease, but its use is associated with a significant risk of T-cell-mediated liver injury in a small number of patients. An important clinical conundrum following the contraindication of tolvaptan is whether administration of agents of similar pharmacological action and structure will be tolerated. Herein, we addressed this question through the exposure of tolvaptan-responsive T-cell clones to similar pharmaceutical agents. Whilst lixivaptan and conivaptan did not activate tolvaptan-responsive T-cells, mozavaptan evoked proliferative responses comparable with tolvaptan itself, indicating that there may be collateral immunological intolerance to this compound as a product of sensitization to tolvaptan.

Curcumin supplementation in pediatric patients: A systematic review of current clinical evidence.

This systematic review was designed to determine the clinical efficacy and safety of curcumin supplementation for pediatric patients based on clinical trials in children. We systematically searched electronic databases including PubMed, EMBASE, Web of Science, and Scopus for all studies that investigated curcumin administration in the pediatric population without any time frame limitation. Finally, we identified 16 studies for this review. Clinical efficacy and safety of curcumin were assessed in children with inflammatory and immune disorders (including asthma, inflammatory bowel disease (IBD), and juvenile idiopathic arthritis (JIA)), metabolic disorders, autosomal dominant polycystic kidney disease (ADPKD), cystic fibrosis (CF), tetralogy of Fallot (TOF), and infectious diseases. Curcumin was administered in a wide range of doses (45 mg-4,000 mg daily) and durations (2-48 weeks). Overall, curcumin was well tolerated in all studies and improved the severity of inflammatory and immune disorders and metabolic diseases. However, more studies are needed to clarify the role of curcumin supplementation among children with ADPKD, CF, TOF, and infectious diseases. Because of substantial heterogeneity in methodological quality, design, outcomes, dose, duration of intake, formulations, and study populations across studies, no quantitative analysis was performed. Additional large-scale, randomized, placebo-controlled clinical trials are needed to confirm the results of the conducted studies.

On the Many Actions of Ouabain: Pro-Cystogenic Effects in Autosomal Dominant Polycystic Kidney Disease.

Ouabain and other cardenolides are steroidal compounds originally discovered in plants. Cardenolides were first used as poisons, but after finding their beneficial cardiotonic effects, they were rapidly included in the medical pharmacopeia. The use of cardenolides to treat congestive heart failure remained empirical for centuries and only relatively recently, their mechanisms of action became better understood. A breakthrough came with the discovery that ouabain and other cardenolides exist as endogenous compounds that circulate in the bloodstream of mammals. This elevated these compounds to the category of hormones and opened new lines of investigation directed to further study their biological role. Another important discovery was the finding that the effect of ouabain was mediated not only by inhibition of the activity of the Na,K-ATPase (NKA), but by the unexpected role of NKA as a receptor and a signal transducer, which activates a complex cascade of intracellular second messengers in the cell. This broadened the interest for ouabain and showed that it exerts actions that go beyond its cardiotonic effect. It is now clear that ouabain regulates multiple cell functions, including cell proliferation and hypertrophy, apoptosis, cell adhesion, cell migration, and cell metabolism in a cell and tissue type specific manner. This review article focuses on the cardenolide ouabain and discusses its various in vitro and in vivo effects, its role as an endogenous compound, its mechanisms of action, and its potential use as a therapeutic agent; placing especial emphasis on our findings of ouabain as a pro-cystogenic agent in autosomal dominant polycystic kidney disease (ADPKD).

Branched-chain amino acids enhance cyst development in autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the progressive development of kidney and liver cysts. The mammalian target of rapamycin (mTOR) cascade is one of the important pathways regulating cyst growth in ADPKD. Branched-chain amino acids (BCAAs), including leucine, play a crucial role to activate mTOR pathway. Therefore, we administered BCAA dissolved in the drinking water to Pkd1flox/flox:Mx1-Cre (cystic) mice from four to 22 weeks of age after polyinosinic-polycytidylic acid-induced conditional Pkd1 knockout at two weeks of age. The BCAA group showed significantly greater kidney/body weight ratio and higher cystic index in both the kidney and liver compared to the placebo-treated mice. We found that the L-type amino acid transporter 1 that facilitates BCAA entry into cells is strongly expressed in cells lining the cysts. We also found increased cyst-lining cell proliferation and upregulation of mTOR and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways in the BCAA group. In vitro, we cultured renal epithelial cell lines from Pkd1 null mice with or without leucine. Leucine was found to stimulate cell proliferation, as well as activate mTOR and MAPK/ERK pathways in these cells. Thus, BCAA accelerated disease progression by mTOR and MAPK/ERK pathways. Hence, BCAA may be harmful to patients with ADPKD.

Ouabain activates the Na-K-ATPase signalosome to induce autosomal dominant polycystic kidney disease cell proliferation.

The Na-K-ATPase is part of a cell signaling complex, the Na-K-ATPase signalosome, which upon activation by the hormone ouabain regulates the function of different cell types. We previously showed that ouabain induces proliferation of epithelial cells derived from renal cysts of patients with autosomal dominant polycystic kidney disease (ADPKD cells). Here, we investigated the signaling pathways responsible for mediating the effects of ouabain in these cells. Incubation of ADPKD cells with ouabain, in concentrations similar to those found in blood, stimulated phosphorylation of the epidermal growth factor receptor (EGFR) and promoted its association to the Na-K-ATPase. In addition, ouabain activated the kinase Src, but not the related kinase Fyn. Tyrphostin AG1478 and PP2, inhibitors of EGFR and Src, respectively, blocked ouabain-dependent ADPKD cell proliferation. Treatment of ADPKD cells with ouabain also caused phosphorylation of the caveolar protein caveolin-1, and disruption of cell caveolae with methyl-ß-cyclodextrin prevented Na-K-ATPase-EGFR interaction and ouabain-induced proliferation of the cells. Downstream effects of ouabain in ADPKD cells included activation of B-Raf and MEK and phosphorylation of the extracellular regulated kinase ERK, which translocated into the ADPKD cell nuclei. Finally, ouabain reduced expression of the cyclin-dependent kinase inhibitors p21 and p27, which are suppressors of cell proliferation. Different from ADPKD cells, ouabain showed no significant effect on B-Raf, p21, and p27 in normal human kidney epithelial cells. Altogether, these results identify intracellular pathways of ouabain-dependent Na-K-ATPase-mediated signaling in ADPKD cells, including EGFR-Src-B-Raf-MEK/ERK, and establish novel mechanisms involved in ADPKD cell proliferation.

Altered Hippo signalling in polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive deterioration of renal function and formation of cysts, and is an important cause of end-stage renal disease. Previously we showed that tubular epithelial injury accelerates cyst formation in inducible Pkd1-deletion mice. In these mice, expression of the planar cell polarity (PCP) component Four-jointed (Fjx1) is decreased during epithelial repair, while in control mice Fjx1 expression is increased and may be required during tissue regeneration. In cystic kidneys, however, Fjx1 expression is also increased. Besides a PCP component, Four-jointed is also implicated in the Hippo-signalling pathway. This pathway is involved in organ size control by regulating proliferation and apoptosis. The role of Hippo signalling, together with the opposing expression pattern of Fjx1 during epithelial repair and at cystic stages, triggered us to investigate the activity of the Hippo pathway during these processes. Therefore, we examined its final effector molecule, the transcriptional co-activator Yes-associated protein (YAP) and observed that during tissue repair, YAP expression was not different between Pkd1-deletion mice and controls, ie during tissue regeneration YAP expression was increased and predominantly localized in the cytoplasm but normalized after tissue repair. At a later stage, however, in cystic epithelia and epithelia of dilated tubules, strong nuclear YAP accumulation was observed, accompanied by up-regulation of the YAP transcriptional targets Birc-3, Ctgf, InhbA, and Fjx1. Altered activity of the Hippo pathway was confirmed in renal tissues from human ADPKD and ARPKD patients, as well as in cystic renal tumours. Our data strengthen the concept that during epithelial repair Four-jointed is involved in PCP signalling, while in cystic kidneys it is related to Hippo signalling and cyst growth.

Renal insufficiency due to angiotensin-converting enzyme inhibitors.

Angiotensin-converting enzyme (ACE) inhibitors represent a major therapeutic breakthrough for treatment of hypertension, congestive heart failure and various chronic renal diseases. They are effective generally well tolerated and safe for most patients. However, acute renal insufficiency or overt renal failure occurs in some patients with underlying critical renal artery stenosis (RAS), hypertensive nephrosclerosis, autosomal dominant polycystic kidney disease, diabetes mellitus, and chronic congestive heart failure. Diuretic-induced sodium depletion and underlying chronic renal insufficiency are the major predisposing factors for renal insufficiency in all of these patient populations. Renal insufficiency is usually asymptomatic, nonoliguric, associated with hyperkalemia, and in nearly every case completely reversible after discontinuation of the offending agent. Moreover, it can usually be managed in the outpatient setting by discontinuation of the ACE inhibitor, concomitant diuretic or both. An asymptomatic increase in serum creatinine in patients administered ACE inhibitors should raise the possibility of RAS; however, more common renal diseases should be considered. The decision to pursue testing for RAS should be done on an individual basis; moreover, it is imperative that patient willingness to undergo invasive procedures including angioplasty and/or surgery should be determined prospectively.