Sirolimus and kidney growth in autosomal dominant polycystic kidney disease

Meckel-Gruber syndrome and the role of primary cilia in kidney, skeleton, and central nervous system development

The ciliopathies are a group of related inherited diseases characterized by malformations in organ development. The diseases affect multiple organ systems, with kidney, skeleton, and brain malformations frequently observed. Research over the last decade has revealed that these diseases are due to defects in primary cilia, essential sensory organelles found on most cells in the human body. Here we discuss the genetic and cell biological basis of one of the most severe ciliopathies, Meckel-Gruber syndrome, and explain how primary cilia contribute to the development of the affected organ systems.

Murine Models of Polycystic Kidney Disease

Polycystic diseases affect approximately 1/1000 and are important causes of kidney failure. No therapies presently are in clinical practice that can prevent disease progression. Multiple mouse models have been produced for the genetic forms of the disease that most commonly affect humans. In this report, we review recent progress in the field and describe some of the outstanding challenges.

Polycystic kidney disease: a case of suppressed autophagy?

Autosomal-dominant polycystic kidney disease is the most common form of polycystic kidney disease in adults and is caused by a mutation in the polycystic kidney disease 1 or 2 genes, which encode, respectively, polycystin-1 and polycystin-2. Autophagy is present in polycystic kidneys in rat and mouse models of polycystic kidney disease. Autophagy has yet to be shown in human polycystic kidney disease kidneys. The mechanism of cyst growth has been studied extensively in vitro and in vivo. Multiple molecules and signaling pathways have been implicated in cyst growth including mammalian target of rapamycin, the renin-angiotensin-aldosterone system, vasopressin and cyclic adenosine monophosphate, epidermal growth factor and insulin-like growth factor tyrosine kinases, vascular endothelial growth factor, extracellular signal-related kinase, tumor necrosis factor-α, cyclin-dependent kinases, caspases and apoptosis, and cyclic adenosine monophosphate-activated protein kinases. Many of the agents that inhibit these signaling pathways and slow cyst growth are also autophagy inducers such as mammalian target of rapamycin inhibitors, cyclin-dependent kinase inhibitors, caspase inhibitors, tyrosine kinase inhibitors, metformin, curcumin, and triptolide. There are reasons to believe that suppression of autophagy may play a role in cyst formation and growth. This review presents the hypothesis that suppression of autophagy may play a role in cyst formation and growth, based on the following: (1) many of the agents that protect against polycystic kidney disease also induce autophagy, (2) suppression of autophagy in polycystic kidney disease 1 knockout cells, (3) a defect in autophagy in congenital polycystic kidney mice with polycystic kidney disease, (4) how suppressed autophagy may relate to apoptosis in polycystic kidney disease, and (5) conditions with defective cilia, the ciliopathies, are associated with decreased autophagy.

Tuberous sclerosis complex, mTOR, and the kidney: report of an NIDDK-sponsored workshop

Remarkable basic and translational advances have elucidated the role of the mammalian target of rapamycin (mTOR) signaling network in the pathogenesis of renal disease. Many of these advances originated from studies of the genetic disease tuberous sclerosis complex (TSC), leading to one of the clearest therapeutic opportunities to target mTOR with rapamycin and its analogs ("rapalogs"), which effectively inhibit mTOR complex 1 (mTORC1) by an allosteric mechanism. Clinical trials based on these discoveries have provided strongly positive therapeutic results in TSC (Bissler JJ, McCormack FX, Young LR, Elwing JM, Chuck G, Leonard JM, Schmithorst VJ, Laor T, Brody AS, Bean J, Salisbury S, Franz DN. N Engl J Med 358: 140-151, 2008; Krueger DA, Care MM, Holland K, Agricola K, Tudor C, Mangeshkar P, Wilson KA, Byars A, Sahmoud T, Franz DN. N Engl J Med 363: 1801-1811, 2010; McCormack FX, Inoue Y, Moss J, Singer LG, Strange C, Nakata K, Barker AF, Chapman JT, Brantly ML, Stocks JM, Brown KK, Lynch JP 3rd, Goldberg HJ, Young LR, Kinder BW, Downey GP, Sullivan EJ, Colby TV, McKay RT, Cohen MM, Korbee L, Taveira-DaSilva AM, Lee HS, Krischer JP, Trapnell BC. N Engl J Med 364: 1595-1606, 2011). In June 2013, the National Institute of Diabetes and Digestive and Kidney Diseases convened a small panel of physicians and scientists working in the field to identify key unknowns and define possible "next steps" in advancing understanding of TSC- and mTOR-dependent renal phenotypes. TSC-associated renal disease, which affects >85% of TSC patients, and was a major topic of discussion, focused on angiomyolipomas and epithelial cysts. The third major topic was the role of mTOR and mTOR inhibition in the pathogenesis and therapy of chronic renal disease. Renal cell carcinoma, while recognized as a manifestation of TSC that occurs in a small fraction of patients, was not the primary focus of this workshop and thus was omitted from panel discussions and from this report.

Polycystin-1 but not polycystin-2 deficiency causes upregulation of the mTOR pathway and can be synergistically targeted with rapamycin and metformin

Autosomal dominant polycystic kidney disease (ADPKD) is caused by loss-of-function mutations in either PKD1 or PKD2 genes, which encode polycystin-1 (TRPP1) and polycystin-2 (TRPP2), respectively. Increased activity of the mammalian target of rapamycin (mTOR) pathway has been shown in PKD1 mutants but is less documented for PKD2 mutants. Clinical trials using mTOR inhibitors were disappointing, while the AMP-activated kinase (AMPK) activator, metformin is not yet tested in patients. Here, we studied the mTOR activity and its upstream pathways in several human and mouse renal cell models with either siRNA or stable knockdown and with overexpression of TRPP2. Our data reveal for the first time differences between TRPP1 and TRPP2 deficiency. In contrast to TRPP1 deficiency, TRPP2-deficient cells did neither display excessive activation of the mTOR-kinase complex nor inhibition of AMPK activity, while ERK1/2 and Akt activity were similarly affected among TRPP1- and TRPP2-deficient cells. Furthermore, cell proliferation was more pronounced in TRPP1 than in TRPP2-deficient cells. Interestingly, combining low concentrations of rapamycin and metformin was more effective for inhibiting mTOR complex 1 activity in TRPP1-deficient cells than either drug alone. Our results demonstrate a synergistic effect of a combination of low concentrations of drugs suppressing the increased mTOR activity in TRPP1-deficient cells. This novel insight can be exploited in future clinical trials to optimize the efficiency and avoiding side effects of drugs in the treatment of ADPKD patients with PKD1 mutations. Furthermore, as TRPP2 deficiency by itself did not affect mTOR signaling, this may underlie the differences in phenotype, and genetic testing has to be considered for selecting patients for the ongoing trials.

Effect of longacting somatostatin analogue on kidney and cyst growth in autosomal dominant polycystic kidney disease (ALADIN): a randomised, placebo-controlled, multicentre trial

BACKGROUND

Autosomal dominant polycystic kidney disease slowly progresses to end-stage renal disease and has no effective therapy. A pilot study suggested that the somatostatin analogue octreotide longacting release (LAR) could be nephroprotective in this context. We aimed to assess the effect of 3 years of octreotide-LAR treatment on kidney and cyst growth and renal function decline in participants with this disorder.

METHODS

We did an academic, multicentre, randomised, single-blind, placebo-controlled, parallel-group trial in five hospitals in Italy. Adult (>18 years) patients with estimated glomerular filtration rate (GFR) of 40 mL/min per 1·73 m(2) or higher were randomly assigned (central allocation by phone with a computerised list, 1:1 ratio, stratified by centre, block size four and eight) to 3 year treatment with two 20 mg intramuscular injections of octreotide-LAR (n=40) or 0·9% sodium chloride solution (n=39) every 28 days. Study physicians and nurses were aware of the allocated group; participants and outcome assessors were masked to allocation. The primary endpoint was change in total kidney volume (TKV), measured by MRI, at 1 year and 3 year follow-up. Analyses were by modified intention to treat. This study is registered with ClinicalTrials.gov, NCT00309283.

FINDINGS

Recruitment was between April 27, 2006, and May 12, 2008. 38 patients in the octreotide-LAR group and 37 patients in the placebo group had evaluable MRI scans at 1 year follow-up, at this timepoint, mean TKV increased significantly less in the octreotide-LAR group (46·2 mL, SE 18·2) compared with the placebo group (143·7 mL, 26·0; p=0·032). 35 patients in each group had evaluable MRI scans at 3 year follow-up, at this timepoint, mean TKV increase in the octreotide-LAR group (220·1 mL, 49·1) was numerically smaller than in the placebo group (454·3 mL, 80·8), but the difference was not significant (p=0·25). 37 (92·5%) participants in the octreotide-LAR group and 32 (82·1%) in the placebo group had at least one adverse event (p=0·16). Participants with serious adverse events were similarly distributed in the two treatment groups. However, four cases of cholelithiasis or acute cholecystitis occurred in the octreotide-LAR group and were probably treatment-related.

INTERPRETATION

These findings provide the background for large randomised controlled trials to test the protective effect of somatostatin analogues against renal function loss and progression to end-stage kidney disease.

FUNDING

Polycystic Kidney Disease Foundation.

Health-related quality of life in patients with autosomal dominant polycystic kidney disease and CKD stages 1-4: a cross-sectional study

BACKGROUND

In people with early autosomal dominant polycystic kidney disease (ADPKD), average total kidney volume (TKV) is 3 times normal and increases by an average of 5% per year despite a seemingly normal glomerular filtration rate (GFR). We hypothesized that increased TKV would be a source of morbidity and diminished quality of life that would be worse in patients with more advanced disease.

STUDY DESIGN

Cross-sectional.

SETTING & PARTICIPANTS

1,043 patients with ADPKD, hypertension, and a baseline estimated GFR (eGFR)> 20mL/min/1.73m(2).

PREDICTORS

(1) eGFR, (2) height-adjusted TKV (htTKV) in patients with eGFR> 60mL/min/1.73m(2).

OUTCOMES

36-Item Short Form Health Survey (SF-36) and the Wisconsin Brief Pain Survey.

MEASUREMENTS

Questionnaires were self-administered. GFR was estimated from serum creatinine using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. htTKV was measured by magnetic resonance imaging.

RESULTS

Back pain was reported by 50% of patients, and 20% experienced it "often, usually, or always." In patients with early disease (eGFR> 60mL/min/1.73m(2)), there was no association between pain and htTKV, except in patients with large kidneys (htTKV> 1,000mL/m). Comparing across eGFR levels and including patients with eGFRs< 60mL/min/1.73m(2), patients with eGFRs of 20-44mL/min/1.73m(2) were significantly more likely to report that pain impacted on their daily lives and had lower SF-36 scores than patients with eGFRs of 45-60 and ≥60mL/min/1.73m(2). Symptoms relating to abdominal fullness were reported by 20% of patients and were related significantly to lower eGFRs in women, but not men.

LIMITATIONS

TKV and liver volume were not measured in patients with eGFR < 60mL/min/1.73m(2). The number of patients with eGFRs< 30mL/min/1.73m(2) is small. Causal inferences are limited by cross-sectional design.

CONCLUSIONS

Pain is a common early symptom in the course of ADPKD, although it is not related to kidney size in early disease (eGFR> 60mL/min/1.73m(2)), except in individuals with large kidneys (htTKV> 1,000 mL/m). Symptoms relating to abdominal fullness and pain are greater in patients with more advanced (eGFR, 20-45mL/min/1.73m(2)) disease and may be due to organ enlargement, especially in women. More research about the role of TKV in quality of life and outcomes of patients with ADPKD is warranted.

Berberine slows cell growth in autosomal dominant polycystic kidney disease cells

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary monogenic disorder characterized by development and enlargement of kidney cysts that lead to loss of renal function. It is caused by mutations in two genes (PKD1 and PKD2) encoding for polycystin-1 and polycystin-2 proteins which regulate different signals including cAMP, mTOR and EGFR pathways. Abnormal activation of these signals following PC1 or PC2 loss of function causes an increased cell proliferation which is a typical hallmark of this disease. Despite the promising findings obtained in animal models with targeted inhibitors able to reduce cystic cell growth, currently, no specific approved therapy for ADPKD is available. Therefore, the research of new more effective molecules could be crucial for the treatment of this severe pathology. In this regard, we have studied the effect of berberine, an isoquinoline quaternary alkaloid, on cell proliferation and apoptosis in human and mouse ADPKD cystic cell lines. Berberine treatment slows cell proliferation of ADPKD cystic cells in a dose-dependent manner and at high doses (100 μg/mL) it induces cell death in cystic cells as well as in normal kidney tubule cells. However, at 10 μg/mL, berberine reduces cell growth in ADPKD cystic cells only enhancing G0/G1 phase of cell cycle and inhibiting ERK and p70-S6 kinases. Our results indicate that berberine shows a selected antiproliferative activity in cellular models for ADPKD, suggesting that this molecule and similar natural compounds could open new opportunities for the therapy of ADPKD patients.

TNF-α blockade is ineffective in animal models of established polycystic kidney disease

Background

Given the large medical burden of polycystic kidney disease (PKD) and recent clinical trial failures, there is a need for novel, safe and effective treatments for the disorder.

Methods

In PCK rat and PKD2^(ws25/w183) mouse models, entanercept was administered once every three days at 5 or 10 mg/kg, once daily. Mozavaptan was administered as a pilot control, provided continuously via milled chow at 0.1%. Animals were assessed for measures of pharmacodynamic response, and improvements in measures of polycystic kidney disease.

Results

Entanercept treatment modulated inflammatory markers, but provided limited therapeutic benefit in multiple animal models of established polycystic kidney disease. Kidney weight, cyst burden and renal function markers remained unchanged following administration of etanercept at various dose levels and multiple treatment durations.

Conclusions

While it remains possible that TNF-α inhibition may be effective in truly preventative settings, our observations suggest this pathway is less likely to exhibit therapeutic or disease-modifying efficacy following the standard clinical diagnosis of disease.

Pathophysiology, epidemiology, classification and treatment options for polycystic liver diseases

Polycystic liver diseases (PLD) represent a group of genetic disorders in which cysts occur in the liver (autosomal dominant polycystic liver disease) or in combination with cysts in the kidneys (autosomal dominant polycystic kidney disease). Regardless of the genetic mutations, the natural history of these disorders is alike. The natural history of PLD is characterized by a continuous increase in the volume and the number of cysts. Both genders are affected; however, women have a higher prevalence. Most patients with PLD are asymptomatic and can be managed conservatively. Severe symptoms can affect 20% of patients who develop massive hepatomegaly with compression of the surrounding organs. Rrarely, patients with PLD suffer from acute complications caused by the torsion of hepatic cysts, intraluminal cystic hemorrhage and infections. The most common methods for the diagnosis of PLD are cross sectional imaging studies. Abdominal ultrasound and computerized tomography are the two most frequently used investigations. Magnetic resonance imaging is more sensitive and specific, and it is a valuable test for patients with intravenous contrast allergies or renal dysfunction. Different treatment modalities are available to physicians caring for these patients. Medical treatment has been ineffective. Percutaneous sclerotherapy, trans-arterial embolization, cyst fenestration, hepatic resection and liver transplantation are indicated to specific groups of patients and have to be tailored according to the extent of disease. This review outlines the current knowledge of the pathophysiology, clinical course, diagnosis and treatment strategies of PLD.

Long-term treatment with mammalian target of rapamycin inhibitor does not benefit patients with autosomal dominant polycystic kidney disease: a meta-analysis

BACKGROUND

The role of the mammalian target of rapamycin (mTOR) inhibition in the treatment of autosomal dominant polycystic kidney disease (ADPKD) remains unclear. This meta-analysis included all randomized controlled trials (RCTs) that used mTOR inhibitors (TORIs) to halt the progression of ADPKD.

METHODS

Databases including MEDLINE, EMBASE, and the Cochrane Library were searched to find relevant trials. RCTs of TORI treatment in patients with ADPKD were included. Effects on the primary outcome [total kidney volume (TKV)] and secondary outcomes [changes in cyst volume (CV) and parenchymal volume (PV), glomerular filtration rate (GFR), proteinuria, and adverse events] were analyzed.

RESULTS

The results of 5 RCTs, which included 619 patients, were analyzed. TORIs did not significantly reduce TKV [mean difference (WMD) -90.01 ml, 95% CI -235.49 to 55.47, p = 0.23; I(2) = 0%; p for heterogeneity = 0.67]. CV decreased after TORI treatment (WMD -15.08 ml, 95% CI -17.82 to -12.34, p < 0.00001), and PV did not change (WMD -0.55 ml, 95% CI -64.55 to 63.45, p = 0.99). There was no significant difference in GFR between the TORI-treated and control groups (WMD 4.94 ml/min, 95% CI -0.81 to 10.68, p = 0.09). Proteinuria was significantly higher in the TORI-treated group than in the control group (standard mean difference 0.27, 95% CI 0.09-0.44, p = 0.002).

CONCLUSION

Long-term treatment with TORIs does not benefit patients with ADPKD.

Looking at the (w)hole: magnet resonance imaging in polycystic kidney disease

Inherited cystic kidney diseases, including autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD), are the most common monogenetic causes of end-stage renal disease (ESRD) in children and adults. While ARPKD is a rare and usually severe pediatric disease, the more common ADPKD typically shows a slowly progressive course leading to ESRD in adulthood. At the present time there is no established disease-modifying treatment for either ARPKD or ADPKD. Various therapeutic approaches are currently under investigation, such as V2 receptor antagonists, somatostatins, and mTOR inhibitors. Renal function remains stable for decades in ADPKD, and thus clinically meaningful surrogate markers to assess therapeutic efficacy are needed. Various studies have pointed out that total kidney volume (TKV) is a potential surrogate parameter for disease severity in ADPKD. Recent trials have therefore measured TKV by magnet resonance imaging (MRI) to monitor and to predict disease progression. Here, we discuss novel insights on polycystic kidney disease (PKD), the value of MRI, and the measurement of TKV in the diagnosis and follow-up of PKD, as well as novel emerging therapeutic strategies for ADPKD.

Patient-reported outcomes in clinical trials of CKD-related therapies: report of a symposium sponsored by the national kidney foundation and the U.S. Food and Drug Administration

The National Kidney Foundation and the U.S. Food and Drug Administration (FDA) convened a symposium in September 2010, bringing together more than 70 experts, including representatives from the FDA, the National Institutes of Health, the Critical Path Institute, nephrologists, patients, and the pharmaceutical industry to discuss the feasibility and process of developing patient-reported outcome (PRO) measures to access how patients feel or function to be used in clinical trials for regulatory review of treatment benefit. Three disease areas were evaluated for development of end point models in which PRO measures may be useful: anemia secondary to chronic kidney disease, autosomal dominant polycystic kidney disease (ADPKD), and nephrotic syndrome. The participants thought it valuable to use observational data to generate hypotheses regarding patient baseline characteristics that are likely to predict clinically important changes in PROs in response to anemia treatment and to design adequately powered blinded randomized controlled trials of anemia treatment using PROs as primary rather than secondary end points. Validated PRO instruments that reflect the patient experience in ADPKD and nephrotic syndrome are essential to incorporate into clinical trials of new therapeutic interventions because glomerular filtration rate decline may occur late in the disease course, at which point therapeutic benefit is less likely. Conference attendees addressed how PRO measures could be used to evaluate, monitor, provide care, and facilitate the introduction of treatments for patients with these challenging conditions.

The role of phospholipase D in modulating the MTOR signaling pathway in polycystic kidney disease

The mammalian target of rapamycin (mTOR) signaling pathway is aberrantly activated in polycystic kidney disease (PKD). Emerging evidence suggests that phospholipase D (PLD) and its product phosphatidic acid (PA) regulate mTOR activity. In this study, we assessed in vitro the regulatory function of PLD and PA on the mTOR signaling pathway in PKD. We found that the basal level of PLD activity was elevated in PKD cells. Targeting PLD by small molecule inhibitors reduced cell proliferation and blocked mTOR signaling, whereas exogenous PA stimulated mTOR signaling and abolished the inhibitory effect of PLD on PKD cell proliferation. We also show that blocking PLD activity enhanced the sensitivity of PKD cells to rapamycin and that combining PLD inhibitors and rapamycin synergistically inhibited PKD cell proliferation. Furthermore, we demonstrate that targeting mTOR did not induce autophagy, whereas targeting PLD induced autophagosome formation. Taken together, our findings suggest that deregulated mTOR pathway activation is mediated partly by increased PLD signaling in PKD cells. Targeting PLD isoforms with pharmacological inhibitors may represent a new therapeutic strategy in PKD.

Loss of cilia suppresses cyst growth in genetic models of autosomal dominant polycystic kidney disease

Kidney cysts occur following inactivation of polycystins in otherwise intact cilia or following complete removal of cilia by inactivation of intraflagellar transport-related proteins. We investigated the mechanisms of cyst formation in these two distinct processes by combining conditional inactivation of polycystins with concomitant ablation of cilia in developing and adult kidney and liver. We found that loss of intact cilia suppresses cyst growth following inactivation of polycystins and that the severity of cystic disease was directly related to the length of time between the initial loss of the polycystin proteins and the subsequent involution of cilia. This cilia-dependent cyst growth was not explained by activation of the MAPK/ERK, mTOR or cAMP pathways and is likely to be distinct from the mechanism of cyst growth following complete loss of cilia. The data establish the existence of a novel pathway defined by polycystin-dependent inhibition and cilia-dependent activation that promotes rapid cyst growth.

Kidney volume and function in autosomal dominant polycystic kidney disease

Background

The significance of total kidney volume (TKV) as a biomarker of kidney function in autosomal dominant polycystic kidney disease (ADPKD) is controversial and has been reappraised.

Methods

Between 2007 and 2012, 64 patients were followed with a mean 39.7-month observation period. TKV measurements by magnetic resonance imaging and estimation of renal function with estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease equation and 24-h urine creatinine clearance were repeated annually.

Results

TKV and its adjusted parameters (height-adjusted, body surface area-adjusted and log-converted TKV [log-TKV]) correlated with eGFR significantly. Among them, the correlation coefficient of log-TKV was most significant (r = −0.6688, p < 0.001). The eGFR slope correlated negatively with TKV slope (p < 0.05). TKV increased faster and became larger as chronic kidney disease (CKD) stage advanced. As age advanced, eGFR declined significantly (p < 0.001), but the eGFR slope remained constant. There was no significant correlation between TKV and age, but the log-TKV slope became smaller as age advanced. If baseline TKV was large, the eGFR slope was steeper (p < 0.05), which suggests that eGFR declines faster in patients with larger kidney volume.

Conclusions

TKV is confirmed as a clinically meaningful surrogate marker in ADPKD. Log-TKV correlates with eGFR most significantly. Higher rates of kidney enlargement and larger kidney volume are associated with a more rapid decrease in kidney function. Kidney function decreased faster as CKD stage advanced, but its declining slope did not change significantly by age, at least after ~30 years of age.

Everolimus does not further reduce polycystic liver volume when added to long acting octreotide: results from a randomized controlled trial

BACKGROUND & AIMS

Polycystic liver disease (PLD) is associated with autosomal dominant polycystic kidney disease (ADPKD) or autosomal dominant polycystic liver disease (PCLD). The resulting hepatomegaly compromises quality of life. Somatostatin analogues reduce PLD volume by approximately 5% when given for 6-12 months. A pilot trial in 16 ADPKD patients demonstrated that sirolimus, an mTOR inhibitor, reduced PLD volume by 26%. The aim of this study was to assess the PLD volume reducing effect of everolimus and octreotide relative to octreotide monotherapy.

METHODS

We designed a randomized controlled trial that compared 48 weeks of everolimus 2.5 mg daily, combined with octreotide 40 mg intramuscularly every 4 weeks, to octreotide monotherapy. We included PCLD and ADPKD patients. Exclusion criteria were MDRD-GFR <60 ml/min/1.73 m(2) and liver volume <2500 ml. Primary outcome was change in liver volume measured with CT-volumetry.

RESULTS

We randomized 44 PLD patients (29 PCLD, 15 ADPKD, 89% female) to treatment with octreotide (n=23) or octreotide-everolimus (n=21). Liver volume decreased by 3.5% (p<0.01) in the monotherapy arm, compared to 3.8% with combination therapy (p<0.01). The difference between treatment arms was not significant (p=0.73).

CONCLUSIONS

Adding everolimus to octreotide in PLD does not increase the liver volume reducing effect of octreotide.

Novel role of ouabain as a cystogenic factor in autosomal dominant polycystic kidney disease

The classic role of the Na-K-ATPase is that of a primary active transporter that utilizes cell energy to establish and maintain transmembrane Na(+) and K(+) gradients to preserve cell osmotic stability, support cell excitability, and drive secondary active transport. Recent studies have revealed that Na-K-ATPase located within cholesterol-containing lipid rafts serves as a receptor for cardiotonic steroids, including ouabain. Traditionally, ouabain was viewed as a toxin produced only in plants, and it was used in relatively high concentrations to experimentally block the pumping action of the Na-K-ATPase. However, the new and unexpected role of the Na-K-ATPase as a signal transducer revealed a novel facet for ouabain in the regulation of a myriad of cell functions, including cell proliferation, hypertrophy, apoptosis, mobility, and metabolism. The seminal discovery that ouabain is endogenously produced in mammals and circulates in plasma has fueled the interest in this endogenous molecule as a potentially important hormone in normal physiology and disease. In this article, we review the role of the Na-K-ATPase as an ion transporter in the kidney, the experimental evidence for ouabain as a circulating hormone, the function of the Na-K-ATPase as a signal transducer that mediates ouabain's effects, and novel results for ouabain-induced Na-K-ATPase signaling in cystogenesis of autosomal dominant polycystic kidney disease.

Sirolimus and non-melanoma skin cancer prevention after kidney transplantation: a meta-analysis

BACKGROUND

Whether sirolimus is useful in the prevention of non-melanoma skin cancer (NMSC) remains unclear and we therefore performed this meta-analysis of randomized controlled trials to test the hypothesis that Sirolimus-based immunosuppression is associated with a decrease in NMSC.

METHODS

The main outcomes were NMSC, squamous-cell carcinoma and basal-cell carcinoma. The pooled risk ratio (RR) with its 95% confidence interval (95%CI) were used to assess the effects.

RESULTS

5 randomized trials involving a total of 1499 patients receiving kidney transplantation were included. Patients undergoing Sirolimus-based immunosuppression had much lower risk of NMSC (RR = 0.49, 95%CI 0.32-0.76, P = 0.001). Subgroup analyses by tumor type showed that Sirolimus-based immunosuppression significantly decreased risk of both squamous-cell carcinoma (RR = 0.58, 95%CI 0.43-0.78, P < 0.001) and basal-cell carcinoma (RR = 0.56, 95%CI 0.37-0.85, P = 0.006). The quality of evidence was high for NMSC, and moderate for squamous-cell carcinoma and basal-cell carcinoma. No evidence of publication bias was observed.

CONCLUSION

High quality evidence suggests that Sirolimus-based immunosuppression decreases risk of non-melanoma skin cancer, and Sirolimus has an antitumoral effect among kidney-transplant recipients.

Tubular secretion of creatinine in autosomal dominant polycystic kidney disease: consequences for cross-sectional and longitudinal performance of kidney function estimating equations

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal tubular cell proliferation and dedifferentiation, which may influence tubular secretion of creatinine (CCr[TS]).

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

We therefore investigated CCr(TS) in patients with ADPKD and controls and studied consequences for the performance of glomerular filtration rate (GFR) estimating equations.

INDEX & REFERENCE TESTS

In patients with ADPKD and healthy controls, we measured GFR as (125)I-iothalamate clearance while simultaneously determining creatinine clearance.

OTHER MEASUREMENTS

24-hour urinary albumin excretion.

RESULTS

In 121 patients with ADPKD (56% men; mean age, 40 ± 11 [SD] years) and 215 controls (48% men; mean age, 53 ± 10 years), measured GFR (mGFR) was 78 ± 30 and 98 ± 17 mL/min/1.73 m(2), respectively, and CCr(TS) was 15.9 ± 10.8 and 10.9 ± 10.6 mL/min/1.73 m(2), respectively (P < 0.001). The higher CCr(TS) in patients with ADPKD remained significant after adjustment for covariates and appeared to be dependent on mGFR. Correlation and accuracy between mGFR and CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) estimated GFR (eGFR) were 0.95 and 99%, respectively; between mGFR and MDRD (Modification of Diet in Renal Disease) Study eGFR, they were 0.93 and 97%, respectively. Values for bias, precision, and accuracy were similar or slightly better than in controls. In addition, change in mGFR during 3 years of follow-up in 45 patients with ADPKD correlated well with change in eGFR.

LIMITATIONS

Cross-sectional, single center.

CONCLUSIONS

CCr(TS) in patients with ADPKD is higher than that in controls, but this effect is limited and observed at only high-normal mGFR. Consequently, the CKD-EPI and MDRD Study equations perform relatively well in estimating GFR and change in GFR in patients with ADPKD.

Mechanistic target of rapamycin inhibitors in solid organ transplantation: from benchside to clinical use

PURPOSE OF REVIEW

Here, we review recent advances and new insights in mechanistic target of rapamycin (mTOR) biology (signalling pathway, kidney biology and immune system), and recent clinical data on mTOR inhibitors related to solid organ transplantation.

RECENT FINDINGS

The mTOR pathway is a major integrator of signals governing protein and lipid biosynthesis and growth factor-driven cell cycle progression. Recent findings have emphasized a critical role of mTOR in cellular homeostasis with a crucial role in podocyte function. Beyond CD8(+) and regulatory T-cell control, mTOR protein is involved in critical biological functions of T helper cells or dendritic cells. New specific inhibitors of mTORC1/C2 are available and shed new light on mTOR functions. Finally, clinical trials have better defined the use of mTOR inhibitors and emphasized their role in cancer prevention.

SUMMARY

The mTOR pathway is considered as a key integrator of multiple inputs that drives numerous biological processes in cell biology. mTOR inhibitors are potent immunosuppressive drugs for solid organ transplantation. Newly designed specific inhibitors of mTOR complex 1 and 2 offer promising therapeutic effects and a better understanding of the pathway. Many conditions may benefit from mTOR inhibition for a short period, but tolerance of treatment in a chronic setting remains a major concern.

Generation of c-Myc transgenic pigs for autosomal dominant polycystic kidney disease

After several decades of research, autosomal dominant polycystic kidney disease (ADPKD) is still incurable and imposes enormous physical, psychological, and economic burdens on patients and their families. Murine models of ADPKD represent invaluable tools for studying this disease. These murine forms of ADPKD can arise spontaneously, or they can be induced via chemical or genetic manipulations. Although these models have improved our understanding of the etiology and pathogenesis of ADPKD, they have not led to effective treatment strategies. The mini-pig represents an effective biomedical model for studying human diseases, as the pig's human-like physiological processes help to understand disease mechanisms and to develop novel therapies. Here, we tried to generate a transgenic model of ADPKD in pigs by overexpressing c-Myc in kidney tissue. Western-blot analysis showed that c-Myc was overexpressed in the kidney, brain, heart, and liver of transgenic pigs. Immunohistochemical staining of kidney tissue showed that exogenous c-Myc predominantly localized to renal tubules. Slightly elevated blood urea nitrogen levels were observed in transgenic pigs 1 month after birth, but no obvious abnormalities were detected after that time. In the future, we plan to subject this model to renal injury in an effort to promote ADPKD progression.

Defective glucose metabolism in polycystic kidney disease identifies a new therapeutic strategy

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by bilateral renal cyst formation. Recent identification of signaling cascades deregulated in ADPKD has led to the initiation of several clinical trials, but an approved therapy is still lacking. Using a metabolomic approach, we identify a pathogenic pathway in this disease that can be safely targeted for therapy. We show that mutation of PKD1 results in enhanced glycolysis in cells in a mouse model of PKD and in kidneys from humans with ADPKD. Glucose deprivation resulted in lower proliferation and higher apoptotic rates in PKD1-mutant cells than in nondeprived cells. Notably, two distinct PKD mouse models treated with 2-deoxyglucose (2DG), to inhibit glycolysis, had lower kidney weight, volume, cystic index and proliferation rates as compared to nontreated mice. These metabolic alterations depend on the extracellular signal-related kinase (ERK) pathway acting in a dual manner by inhibiting the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) axis on the one hand while activating the mTOR complex 1 (mTORC1)-glycolytic cascade on the other. Enhanced metabolic rates further inhibit AMPK. Forced activation of AMPK acts in a negative feedback loop, restoring normal ERK activity. Taken together, these data indicate that defective glucose metabolism is intimately involved in the pathobiology of ADPKD. Our findings provide a strong rationale for a new therapeutic strategy using existing drugs, either individually or in combination.

Targets, trends, excesses, and deficiencies: refocusing clinical investigation to improve patient outcomes

Clinical trials in nephrology have focused on achieving targets, supplementing deficiencies, and correcting excesses in order to improve patient outcomes. The majority of interventions have failed to demonstrate benefit and some have caused harm. It may be that therapies aiming to 'normalize' parameters may actually disturb evolutionary adaptation, thus causing harm. By refocusing on the physiology of disease, and complexity of adaptation, we may design better trials. We review successful and unsuccessful trials in nephrology and other disciplines and suggest a set of principles by which to design future clinical trials:(1) acknowledge heterogeneity of chronic kidney disease populations and appropriately characterize populations for studies; (2) develop better validated biomarkers (through proteomics, genomics, and metabolomics) to identify responders and nonresponders to interventions; (3) design interventions that mimic physiological processes without collateral detrimental effects; (4) reconsider the status of the randomized-controlled trial as the only 'gold standard' and perform large-scale pragmatic trials comparing current care with the intervention(s) of interest, and (5) broaden nephrology research culture so that the majority of patients are enrolled into observational cohorts and intervention studies, which foster greater knowledge acquisition and dissemination. Improved understanding of pathophysiological mechanisms, in conjunction with more innovative but stringent clinical trial design, will ultimately lead to improved patient outcomes.

Cyst expansion and regression in a mouse model of polycystic kidney disease

Autosomal-dominant polycystic kidney disease is characterized by progressive cyst formation and fibrosis in the kidneys. Here we describe an orthologous Pkd1(nl,nl) mouse model, with reduced expression of the normal Pkd1 transcript, on a fixed genetic background of equal parts C57Bl/6 and 129Ola/Hsd mice (B6Ola-Pkd1(nl,nl)). In these mice, the first cysts develop from mature proximal tubules around birth. Subsequently, larger cysts become visible at day 7, followed by distal tubule and collecting duct cyst formation, and progressive cystic enlargement to develop into large cystic kidneys within 4 weeks. Interestingly, cyst expansion was followed by renal volume regression due to cyst collapse. This was accompanied by focal formation of fibrotic areas, an increased expression of genes involved in matrix remodeling and subsequently an increase in infiltrating immune cells. After an initial increase in blood urea within the first 4 weeks, renal function remained stable over time and the mice were able to survive up to a year. Also, in kidneys of ADPKD patients collapsed cysts were observed, in addition to massive fibrosis and immune infiltrates. Thus, B6Ola-Pkd1(nl,nl) mice show regression of cysts and renal volume that is not accompanied by a reduction in blood urea levels.

Multidrug therapy for polycystic kidney disease: a review and perspective

Autosomal dominant polycystic kidney disease (ADPKD) is a renal disorder characterized by the development of cysts in both kidneys leading to end-stage renal disease (ESRD) by the fifth decade of life. Cysts also occur in other organs, and phenotypic alterations also involve the cardiovascular system. Mutations in the PKD1 and PKD2 genes codifying for polycystin-1 (PC1) and polycystin-2 (PC2) are responsible for the 85 and 15% of ADPKD cases, respectively. PC1 and PC2 defects cause similar symptoms; however, lesions of PKD1 gene are associated with earlier disease onset and faster ESRD progression. The development of kidney cysts requires a somatic 'second hit' to promote focal cyst formation, but also acute renal injury may affect cyst expansion, constituting a 'third hit'. PC1 and PC2 interact forming a complex that regulates calcium homeostasis. Mutations of polycystins induce alteration of Ca(2+) levels likely through the elevation of cAMP. Furthermore, PC1 loss of function also induces activation of mTOR and EGFR signaling. Impaired cAMP, mTOR and EGFR signals lead to activation of a number of processes stimulating both cell proliferation and fluid secretion, contributing to cyst formation and enlargement. Consistently, the inhibition of mTOR, EGFR activity and cAMP accumulation ameliorates renal function in ADPKD animal models, but in ADPKD patients mild results have been shown. Here we briefly review major ADPKD-related pathways, their inhibition and effects on disease progression. Finally, we suggest to reduce abnormal cell proliferation with possible clinical amelioration of ADPKD patients by combined inhibition of cAMP-, EGFR- and mTOR-related pathways.

Efficacy and safety of mTOR inhibitor therapy in patients with early-stage autosomal dominant polycystic kidney disease: a meta-analysis of randomized controlled trials

BACKGROUND

The objective of this study was to conduct a meta-analysis of randomized controlled trials (RCTs) to present a profound review and an objective appraisal of the efficacy and safety of the mammalian target of rapamycin (mTOR) inhibitor therapy in patients with autosomal dominant polycystic kidney disease (ADPKD).

METHODS

RCTs involving the mTOR inhibitor therapy in patients with ADPKD are included. The data of studies and major outcomes include changes in patients' glomerular filtration rate (GFR), urinary protein, total kidney volume (TKV), cyst volume, parenchymal volume, and lipid profile and the frequency of adverse events. Review Manager 5.0 for meta-analysis was used in this study.

RESULTS

Up to January 31, 2011, 4 RCTs (with a total of 564 patients) were included. The mTOR inhibitor therapy group had smaller TKV than the control group [weighted mean difference (WMD) of TKV after treatment: -318.45, P = 0.04]. The mTOR inhibitor treatment does not necessarily slow down the aggravation of renal function in patients with ADPKD (WMD of GFR after therapy: 5.55, P < 0.01; at 6-month analyses = -0.97, P = 0.56). Side effects could occur during the mTOR inhibitor therapy, but the severities can be controlled by the appropriate use of drug.

CONCLUSIONS

Based on the current limited clinical trials, this study suggests that short-duration mTOR inhibitor therapy is relatively safe to slow down the increase in kidney volume in patients with early-stage ADPKD, but it has limited impact on slowing down the decrease in GFR.

Diagnosis and management of polycystic liver disease

Polycystic liver disease (PLD) is arbitrarily defined as a liver that contains >20 cysts. The condition is associated with two genetically distinct diseases: as a primary phenotype in isolated polycystic liver disease (PCLD) and as an extrarenal manifestation in autosomal dominant polycystic kidney disease (ADPKD). Processes involved in hepatic cystogenesis include ductal plate malformation with concomitant abnormal fluid secretion, altered cell-matrix interaction and cholangiocyte hyperproliferation. PLD is usually a benign disease, but can cause debilitating abdominal symptoms in some patients. The main risk factors for growth of liver cysts are female sex, exogenous oestrogen use and multiple pregnancies. Ultrasonography is very useful for achieving a correct diagnosis of a polycystic liver and to differentiate between ADPKD and PCLD. Current radiological and surgical therapies for symptomatic patients include aspiration-sclerotherapy, fenestration, segmental hepatic resection and liver transplantation. Medical therapies that interact with regulatory mechanisms controlling expansion and growth of liver cysts are under investigation. Somatostatin analogues are promising; several clinical trials have shown that these drugs can reduce the volume of polycystic livers. The purpose of this Review is to provide an update on the diagnosis and management of PLD with a focus on literature published in the past 4 years.

Experimental therapies and ongoing clinical trials to slow down progression of ADPKD

The improvement of imaging techniques over the years has contributed to the understanding of the natural history of autosomal dominant polycystic kidney disease, and facilitated the observation of its structural progression. Advances in molecular biology and genetics have made possible a greater understanding of the genetics, molecular, and cellular pathophysiologic mechanisms responsible for its development and have laid the foundation for the development of potential new therapies. Therapies targeting genetic mechanisms in ADPKD have inherent limitations. As a result, most experimental therapies at the present time are aimed at delaying the growth of the cysts and associated interstitial inflammation and fibrosis by targeting tubular epithelial cell proliferation and fluid secretion by the cystic epithelium. Several interventions affecting many of the signaling pathways disrupted in ADPKD have been effective in animal models and some are currently being tested in clinical trials.

Construction of a transgenic pig model overexpressing polycystic kidney disease 2 (PKD2) gene

Autosomal dominant polycystic kidney disease (ADPKD) is a common human genetic disease, affecting millions of people worldwide. The progressive growth of cysts in kidneys eventually leads to renal failure in 50 % of patients, and there is currently no effective treatment. Various murine models have been studied to elucidate the disease mechanisms, and much information has been acquired. However, the course of the disease cannot be fully recapitulated using these models. The pig is a suitable model for biomedical research, and pig PKD2 has high similarity to the human ortholog at the molecular level. Here, a mini-pig PKD2 transgenic model was generated, driven by a ubiquitous cytomegalovirus enhancer/promoter. Using somatic cell nuclear transfer, four transgenic pigs with approximately 10 insertion events each were generated. Quantitative real-time PCR and western blotting showed that PKD2 was more highly expressed in transgenic pigs than in wild-type counterparts. Because of the chronic nature of ADPKD, blood urea nitrogen and serum creatinine levels were continuously measured to assess the pig kidney function. The transgenic pigs continue to show no significant alteration in kidney function; it is estimated that 1-2 more years may be required for manifestation of renal cystogenesis in these pigs.

Urinary proteomic biomarkers for diagnosis and risk stratification of autosomal dominant polycystic kidney disease: a multicentric study

Treatment options for autosomal dominant polycystic kidney disease (ADPKD) will likely become available in the near future, hence reliable diagnostic and prognostic biomarkers for the disease are strongly needed. Here, we aimed to define urinary proteomic patterns in ADPKD patients, which aid diagnosis and risk stratification. By capillary electrophoresis online coupled to mass spectrometry (CE-MS), we compared the urinary peptidome of 41 ADPKD patients to 189 healthy controls and identified 657 peptides with significantly altered excretion, of which 209 could be sequenced using tandem mass spectrometry. A support-vector-machine based diagnostic biomarker model based on the 142 most consistent peptide markers achieved a diagnostic sensitivity of 84.5% and specificity of 94.2% in an independent validation cohort, consisting of 251 ADPKD patients from five different centers and 86 healthy controls. The proteomic alterations in ADPKD included, but were not limited to markers previously associated with acute kidney injury (AKI). The diagnostic biomarker model was highly specific for ADPKD when tested in a cohort consisting of 481 patients with a variety of renal and extrarenal diseases, including AKI. Similar to ultrasound, sensitivity and specificity of the diagnostic score depended on patient age and genotype. We were furthermore able to identify biomarkers for disease severity and progression. A proteomic severity score was developed to predict height adjusted total kidney volume (htTKV) based on proteomic analysis of 134 ADPKD patients and showed a correlation of r = 0.415 (p<0.0001) with htTKV in an independent validation cohort consisting of 158 ADPKD patients. In conclusion, the performance of peptidomic biomarker scores is superior to any other biochemical markers of ADPKD and the proteomic biomarker patterns are a promising tool for prognostic evaluation of ADPKD.

Epidemiology of autosomal-dominant polycystic kidney disease: an in-depth clinical study for south-western Germany

BACKGROUND

As we emerge into the genomic medicine era, the epidemiology of diseases is taken for granted. Accurate prevalence figures, especially of rare diseases (RDs, ≤50/100,000), will become even more important for purposes of health care and societal planning. We noticed that the numbers of affected individuals in regionally established registries for mainly hereditary RDs do not align with published estimated and expected prevalence figures. We therefore hypothesized that such non-population-based means overestimate RDs and sought to address this by recalculating prevalence for an important 'common' hereditary disease, autosomal-dominant polycystic kidney disease (ADPKD) whereby presumed-prevalence is 100-250/100,000 METHODS: The Else-Kroener-Fresenius-ADPKD-Study in south-west Germany with a population of 2,727,351 inhabitants was established with the cooperation of all nephrology centres. Furthermore, general practitioners, internists, urologists, human geneticists and neurosurgery centres were contacted with questionnaires for demographic, family and kidney function data. Germline-mutation screening of susceptibility genes PKD1 and PKD2 was offered. Official population data for 2010 were used for overall and kidney function-adjusted prevalence estimations.

RESULTS

A total of 891 subjects, 658 index-cases and 233 relatives, aged 10-89 (mean 52), were registered, with >90% response rate, 398 by nephrologists and 493 by non-nephrologists. Molecular-genetic analyses contributed to confirmation of the diagnosis in 57%. The overall prevalence of ADPKD was 32.7/100,000 reaching a maximum of 57.3/100,000 in the 6th decade of life.

CONCLUSIONS

Prevalence of ADPKD is overestimated by 2- to 5-fold and close to the limit of RDs which may be of broad clinical, logistic and policy implications.

Cystic kidney diseases: many ways to form a cyst

Renal cysts are a common radiological finding in both adults and children. They occur in a variety of conditions, and the clinical presentation, management, and prognosis varies widely. In this article, we discuss the major causes of renal cysts in children and adults with a particular focus on the most common genetic forms. Many cystoproteins have been localized to the cilia centrosome complex (CCC). We consider the evidence for a universal 'cilia hypothesis' for cyst formation and the evidence for non-ciliary proteins in cyst formation.

MicroRNAs and Polycystic Kidney Disease

Polycystic kidney disease (PKD), the most common genetic cause of chronic renal failure, is characterized by the presence of numerous fluid-filled cysts in renal parenchyma. Despite recent progress, no FDA-approved therapy is available to retard cyst growth. Here, we review current evidence implicating two groups of miRNAs - the miR-17~92 cluster and miR-200s - in the pathogenesis of PKD. We present a new hypothesis for cyst growth involving miRNAs and regulation of PKD gene dosage. We propose that manipulating miRNA function in an attempt to normalize PKD gene dosage represents a novel therapeutic strategy in PKD.

Tolvaptan in patients with autosomal dominant polycystic kidney disease

BACKGROUND

The course of autosomal dominant polycystic kidney disease (ADPKD) is often associated with pain, hypertension, and kidney failure. Preclinical studies indicated that vasopressin V(2)-receptor antagonists inhibit cyst growth and slow the decline of kidney function.

METHODS

In this phase 3, multicenter, double-blind, placebo-controlled, 3-year trial, we randomly assigned 1445 patients, 18 to 50 years of age, who had ADPKD with a total kidney volume of 750 ml or more and an estimated creatinine clearance of 60 ml per minute or more, in a 2:1 ratio to receive tolvaptan, a V(2)-receptor antagonist, at the highest of three twice-daily dose regimens that the patient found tolerable, or placebo. The primary outcome was the annual rate of change in the total kidney volume. Sequential secondary end points included a composite of time to clinical progression (defined as worsening kidney function, kidney pain, hypertension, and albuminuria) and rate of kidney-function decline.

RESULTS

Over a 3-year period, the increase in total kidney volume in the tolvaptan group was 2.8% per year (95% confidence interval [CI], 2.5 to 3.1), versus 5.5% per year in the placebo group (95% CI, 5.1 to 6.0; P<0.001). The composite end point favored tolvaptan over placebo (44 vs. 50 events per 100 follow-up-years, P=0.01), with lower rates of worsening kidney function (2 vs. 5 events per 100 person-years of follow-up, P<0.001) and kidney pain (5 vs. 7 events per 100 person-years of follow-up, P=0.007). Tolvaptan was associated with a slower decline in kidney function (reciprocal of the serum creatinine level, -2.61 [mg per milliliter](-1) per year vs. -3.81 [mg per milliliter](-1) per year; P<0.001). There were fewer ADPKD-related adverse events in the tolvaptan group but more events related to aquaresis (excretion of electrolyte-free water) and hepatic adverse events unrelated to ADPKD, contributing to a higher discontinuation rate (23%, vs. 14% in the placebo group).

CONCLUSIONS

Tolvaptan, as compared with placebo, slowed the increase in total kidney volume and the decline in kidney function over a 3-year period in patients with ADPKD but was associated with a higher discontinuation rate, owing to adverse events. (Funded by Otsuka Pharmaceuticals and Otsuka Pharmaceutical Development and Commercialization; TEMPO 3:4 ClinicalTrials.gov number, NCT00428948.).

Urine proteome of autosomal dominant polycystic kidney disease patients

Background

Autosomal dominant polycystic kidney disease (ADPKD) is responsible for 10% of cases of the end stage renal disease. Early diagnosis, especially of potential fast progressors would be of benefit for efficient planning of therapy. Urine excreted proteome has become a promising field of the search for marker patterns of renal diseases including ADPKD. Up to now however, only the low molecular weight fraction of ADPKD proteomic fingerprint was studied. The aim of our study was to characterize the higher molecular weight fraction of urinary proteome of ADPKD population in comparison to healthy controls as a part of a general effort aiming at exhaustive characterization of human urine proteome in health and disease, preceding establishment of clinically useful disease marker panel.

Results

We have analyzed the protein composition of urine retentate (>10 kDa cutoff) from 30 ADPKD patients and an appropriate healthy control group by means of a gel-free relative quantitation of a set of more than 1400 proteins. We have identified an ADPKD-characteristic footprint of 155 proteins significantly up- or downrepresented in the urine of ADPKD patients. We have found changes in proteins of complement system, apolipoproteins, serpins, several growth factors in addition to known collagens and extracellular matrix components. For a subset of these proteins we have confirmed the results using an alternative analytical technique.

Conclusions

Obtained results provide basis for further characterization of pathomechanism underlying the observed differences and establishing the proteomic prognostic marker panel.

Serum uric acid, kidney volume and progression in autosomal-dominant polycystic kidney disease

BACKGROUND

Hyperuricemia has been implicated in the development and progression of chronic kidney disease, both in animal experiments and in clinical studies. As a potentially modifiable risk factor, we examined whether serum uric acid levels correlate with early hypertension, kidney volume and progression to end-stage renal disease (ESRD) in autosomal-dominant polycystic kidney disease (ADPKD).

METHODS

Retrospective analysis of a prospective observational study of the natural history of ADPKD, conducted at the University of Colorado between 1985 and 2005. Included are 680 ADPKD adults who provided data on blood pressure, renal volume, renal function, uric acid, age at the onset of ESRD or last known age without ESRD. Serum uric acid levels were examined as a continuous variable and as gender-specific quartiles. The main outcome of interest was age at the onset of ESRD; secondary outcomes were hypertension onset before age 30 years and total kidney volume (TKV) at the study visit.

RESULTS

Subjects with early-onset hypertension had higher age-adjusted serum uric acid levels than those with no or late-onset hypertension despite similar creatinine clearance. After adjusting for age, gender and creatinine clearance, there was a 5.8% increase in TKV and 4.1% increase in TKV/body surface area for every 1 mg/dL increase in uric acid (P = 0.007). The multivariate-adjusted Cox regression demonstrated a greater hazard ratio for ESRD for subjects in the 4th and 3rd quartiles of uric acid compared with the 1st [4.8 (2.6-8.9; P < 0.001) and 2.9 (1.6-5.3; P < 0.001)].

CONCLUSIONS

Higher serum uric acid levels are associated with earlier onset of hypertension, larger kidney volume and increased hazard for ESRD in ADPKD independent of gender, body mass index and renal function at the study visit. Randomized interventional studies will be necessary to examine whether treating hyperuricemia has a protective role in ADPKD.

Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and potential therapies

Autosomal dominant polycystic kidney disease (ADPKD) is the most common progressive hereditary kidney disease. In 85-90% of cases, ADPKD results from a mutation in the PKD1 gene, and the other 10-15% of the cases are accounted for by mutations in PKD2. PKD1 and PKD2 encode polycystin-1 and polycystin-2. Polycystin-1 may be a receptor that controls the channel activity of polycystin-2 as part of the polycystin signaling complex. ADPKD is characterized by the progressive development of fluid-filled cysts derived from renal tubular epithelial cells that gradually compress the parenchyma and compromise renal function. In recent years, considerable interest has developed in the primary cilia as a site of the proteins that are involved in renal cystogenesis. The pathological processes that facilitate cyst enlargement are hypothesized to result from two specific cellular abnormalities: (1) increased fluid secretion into the cyst lumen and (2) inappropriately increased cell division by the epithelium lining the cyst. Since there is no clinically approved specific or targeted therapy, current practice focuses on blood pressure control and statin therapy to reduce the cardiac mortality associated with chronic kidney disease. However, recent advances in our understanding of the pathways that govern renal cystogenesis have led to a number of intriguing possibilities in regard to therapeutic interventions. The purpose of this article is to review the pathogenesis of renal cyst formation and to review novel targets for the treatment of ADPKD.

Low-dose oral sirolimus and the risk of menstrual-cycle disturbances and ovarian cysts: analysis of the randomized controlled SUISSE ADPKD trial

Sirolimus has been approved for clinical use in non proliferative and proliferative disorders. It inhibits the mammalian target of rapamycin (mTOR) signaling pathway which is also known to regulate ovarian morphology and function. Preliminary observational data suggest the potential for ovarian toxicity but this issue has not been studied in randomized controlled trials. We reviewed the self-reported occurrence of menstrual cycle disturbances and the appearance of ovarian cysts post hoc in an open label randomized controlled phase II trial conducted at the University Hospital Zürich between March 2006 and March 2010. Adult females with autosomal dominant polycystic kidney disease, an inherited kidney disease not known to affect ovarian morphology and function, were treated with 1.3 to 1.5 mg sirolimus per day for a median of 19 months (N = 21) or standard care (N = 18). Sirolimus increased the risk of both oligoamenorrhea (hazard ratio [HR] 4.3, 95% confidence interval [CI] 1.1 to 29) and ovarian cysts (HR 4.4, CI 1.1 to 26); one patient was cystectomized five months after starting treatment with sirolimus. We also studied mechanisms of sirolimus-associated ovarian toxicity in rats. Sirolimus amplified signaling in rat ovarian follicles through the pro-proliferative phosphatidylinositol 3-kinase pathway. Low dose oral sirolimus increases the risk of menstrual cycle disturbances and ovarian cysts and monitoring of sirolimus-associated ovarian toxicity is warranted and might guide clinical practice with mammalian target of rapamycin inhibitors.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00346918.

CDK inhibitors R-roscovitine and S-CR8 effectively block renal and hepatic cystogenesis in an orthologous model of ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) and other forms of PKD are associated with dysregulated cell cycle and proliferation. Although no effective therapy for the treatment of PKD is currently available, possible mechanism-based approaches are beginning to emerge. A therapeutic intervention targeting aberrant cilia-cell cycle connection using CDK-inhibitor R-roscovitine showed effective arrest of PKD in jck and cpk models that are not orthologous to human ADPKD. To evaluate whether CDK inhibition approach will translate into efficacy in an orthologous model of ADPKD, we tested R-roscovitine and its derivative S-CR8 in a model with a conditionally inactivated Pkd1 gene (Pkd1 cKO). Similar to ADPKD, Pkd1 cKO mice developed renal and hepatic cysts. Treatment of Pkd1 cKO mice with R-roscovitine and its more potent and selective analog S-CR8 significantly reduced renal and hepatic cystogenesis and attenuated kidney function decline. Mechanism of action studies demonstrated effective blockade of cell cycle and proliferation and reduction of apoptosis. Together, these data validate CDK inhibition as a novel and effective approach for the treatment of ADPKD.

Mammalian target of rapamycin inhibition in polycystic kidney disease: From bench to bedside

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease in the USA resulting in chronic kidney disease and the need for dialysis and transplantation. Approximately 85% of cases of ADPKD are caused by a mutation in the Pkd1 gene that encodes polycystin-1, a large membrane receptor. The Pkd1 gene mutation results in abnormal proliferation in tubular epithelial cells, which plays a crucial role in cyst development and/or growth in PKD. Activation of the proliferative mammalian target of rapamycin (mTOR) signaling pathway has been demonstrated in polycystic kidneys from rodents and humans. mTOR inhibition with sirolimus or everolimus decreases cysts in most animal models of PKD including Pkd1 and Pkd2 gene deficient orthologous models of human disease. On the basis of animal studies, human studies were undertaken. Two large randomized clinical trials published in the New England Journal of Medicine of everolimus or sirolimus in ADPKD patients were very unimpressive and associated with a high side-effect profile. Possible reasons for the unimpressive nature of the human studies include their short duration, the high drop-out rate, suboptimal dosing, lack of randomization of "fast" and "slow progressors" and the lack of correlation between kidney size and kidney function in ADPKD. The future of mTOR inhibition in ADPKD is discussed.

Folate-conjugated rapamycin slows progression of polycystic kidney disease

Activation of the mammalian target of rapamycin (mTOR) signaling pathway is aberrant in autosomal-dominant polycystic kidney disease (ADPKD). The mTOR inhibitors, such as rapamycin, ameliorate PKD in rodent models, but clinical trials have not shown benefit, possibly as a result of low tissue concentrations of rapamycin at clinically tolerable doses. To overcome this limitation, we synthesized a folate-conjugated form of rapamycin (FC-rapa) that is taken up by folate receptor-mediated endocytosis and cleaved intracellularly to reconstitute the active drug. We found that renal cyst-lining cells highly express the folate receptor in ADPKD and mouse models. In vitro, FC-rapa inhibited mTOR activity in a dose- and folate receptor-dependent manner. Treatment of a PKD mouse model with FC-rapa inhibited mTOR in the target tissue, strongly attenuated proliferation and growth of renal cysts and preserved renal function. Furthermore, FC-rapa inhibited mTOR activity in the kidney but not in other organs. In summary, these results suggest that targeting the kidney using FC-rapa may overcome the significant side effects and lack of renal efficacy observed in clinical trials with mTOR inhibitors in ADPKD.

Sirolimus and secondary skin-cancer prevention in kidney transplantation

BACKGROUND

Transplant recipients in whom cutaneous squamous-cell carcinomas develop are at high risk for multiple subsequent skin cancers. Whether sirolimus is useful in the prevention of secondary skin cancer has not been assessed.

METHODS

In this multicenter trial, we randomly assigned transplant recipients who were taking calcineurin inhibitors and had at least one cutaneous squamous-cell carcinoma either to receive sirolimus as a substitute for calcineurin inhibitors (in 64 patients) or to maintain their initial treatment (in 56). The primary end point was survival free of squamous-cell carcinoma at 2 years. Secondary end points included the time until the onset of new squamous-cell carcinomas, occurrence of other skin tumors, graft function, and problems with sirolimus.

RESULTS

Survival free of cutaneous squamous-cell carcinoma was significantly longer in the sirolimus group than in the calcineurin-inhibitor group. Overall, new squamous-cell carcinomas developed in 14 patients (22%) in the sirolimus group (6 after withdrawal of sirolimus) and in 22 (39%) in the calcineurin-inhibitor group (median time until onset, 15 vs. 7 months; P=0.02), with a relative risk in the sirolimus group of 0.56 (95% confidence interval, 0.32 to 0.98). There were 60 serious adverse events in the sirolimus group, as compared with 14 such events in the calcineurin-inhibitor group (average, 0.938 vs. 0.250). There were twice as many serious adverse events in patients who had been converted to sirolimus with rapid protocols as in those with progressive protocols. In the sirolimus group, 23% of patients discontinued the drug because of adverse events. Graft function remained stable in the two study groups.

CONCLUSIONS

Switching from calcineurin inhibitors to sirolimus had an antitumoral effect among kidney-transplant recipients with previous squamous-cell carcinoma. These observations may have implications concerning immunosuppressive treatment of patients with cutaneous squamous-cell carcinomas. (Funded by Hospices Civils de Lyon and others; TUMORAPA ClinicalTrials.gov number, NCT00133887.).

Constitutive activation of the mTOR signaling pathway within the normal glomerulus

Agents that target the activity of the mammalian target of rapamycin (mTOR) kinase in humans are associated with proteinuria. However, the mechanisms underlying mTOR activity and signaling within the kidney are poorly understood. In this study, we developed a sensitive immunofluorescence technique for the evaluation of activated pmTOR and its associated signals in situ. While we find that pmTOR is rarely expressed in normal non-renal tissues, we consistently find intense expression in glomeruli within normal mouse and human kidneys. Using double staining, we find that the expression of pmTOR co-localizes with nephrin in podocytes and expression appears minimal within other cell types in the glomerulus. In addition, we found that pmTOR was expressed on occasional renal tubular cells within mouse and human kidney specimens. We also evaluated mTOR signaling in magnetic bead-isolated glomeruli from normal mice and, by Western blot analysis, we confirmed function of the pathway in glomerular cells vs. interstitial cells. Furthermore, we found that the activity of the pathway as well as the expression of VEGF, a target of mTOR-induced signaling, were reduced within glomeruli of mice following treatment with rapamycin. Collectively, these findings demonstrate that the mTOR signaling pathway is constitutively hyperactive within podocytes. We suggest that pmTOR signaling functions to regulate glomerular homeostasis in part via the inducible expression of VEGF.