New treatments for autosomal dominant polycystic kidney disease

Discovery of putative inhibitors of human Pkd1 enzyme: Molecular docking, dynamics and simulation, QSAR, and MM/GBSA

Polycystic kidney disease is the most prevalent hereditary kidney disease globally and is mainly linked to the overexpression of a gene called PKD1. To date, there is no effective treatment available for polycystic kidney disease, and the practicing treatments only provide symptomatic relief. Discovery of the compounds targeting the PKD1 gene by inhibiting its expression under the disease condition could be crucial for effective drug development. In this study, a molecular docking and molecular dynamic simulation, QSAR, and MM/GBSA-based approaches were used to determine the putative inhibitors of the Pkd1 enzyme from a library of 1379 compounds. Initially, fourteen compounds were selected based on their binding affinities with the Pkd1 enzyme using MOE and AutoDock tools. The selected drugs were further investigated to explore their properties as drug candidates and the stability of their complex formation with the Pkd1 enzyme. Based on the physicochemical and ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) properties, and toxicity profiling, two compounds including olsalazine and diosmetin were selected for the downstream analysis as they demonstrated the best drug-likeness properties and highest binding affinity with Pkd1 in the docking experiment. Molecular dynamic simulation using Gromacs further confirmed the stability of olsalazine and diosmetin complexes with Pkd1 and establishing interaction through strong bonding with specific residues of protein. High biological activity and binding free energies of two complexes calculated using 3D QSAR and Schrodinger module, respectively further validated our results. Therefore, the molecular docking and dynamics simulation-based in-silico approach used in this study revealed olsalazine and diosmetin as potential drug candidates to combat polycystic kidney disease by targeting Pkd1 enzyme.

Pharmacological Effects of Panduratin A on Renal Cyst Development in In Vitro and In Vivo Models of Polycystic Kidney Disease

Renal cyst expansion in polycystic kidney disease (PKD) involves abnormalities in both cyst-lining-cell proliferation and fluid accumulation. Suppression of these processes may retard the progression of PKD. Evidence suggests that the activation of 5' AMP-activated protein kinase (AMPK) inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride secretion, leading to reduced progression of PKD. Here we investigated the pharmacological effects of panduratin A, a bioactive compound known as an AMPK activator, on CFTR-mediated chloride secretion and renal cyst development using in vitro and animal models of PKD. We demonstrated that AMPK was activated in immortalized normal renal cells and autosomal dominant polycystic kidney disease (ADPKD) cells following treatment with panduratin A. Treatment with panduratin A reduced the number of renal cyst colonies corresponding with a decrease in cell proliferation and phosphorylated p70/S6K, a downstream target of mTOR signaling. Additionally, panduratin A slowed cyst expansion via inhibition of the protein expression and transport function of CFTR. In heterozygous Han:Sprague-Dawley (Cy/+) rats, an animal model of PKD, intraperitoneal administration of panduratin A (25 mg/kg BW) for 5 weeks significantly decreased the kidney weight per body weight ratios and the cystic index. Panduratin A also reduced collagen deposition in renal tissue. Intraperitoneal administration of panduratin A caused abdominal bleeding and reduced body weight. However, 25 mg/kg BW of panduratin A via oral administration in the PCK rats, another non-orthologous PKD model, showed a significant decrease in the cystic index without severe adverse effects, indicating that the route of administration is critical in preventing adverse effects while still slowing disease progression. These findings reveal that panduratin A might hold therapeutic properties for the treatment of PKD.

Recent Discoveries in Epigenetic Modifications of Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a heritable renal disease that results in end-stage kidney disease, due to the uncontrolled bilateral growth of cysts throughout the kidneys. While it is known that a mutation within a PKD-causing gene is required for the development of ADPKD, the underlying mechanism(s) causing cystogenesis and progression of the disease are not well understood. Limited therapeutic options are currently available to slow the rate of cystic growth. Epigenetic modifications, including DNA methylation, are known to be altered in neoplasia, and several FDA-approved therapeutics target these disease-specific changes. As there are many similarities between ADPKD and neoplasia, we (and others) have postulated that ADPKD kidneys contain alterations to their epigenetic landscape that could be exploited for future therapeutic discovery. Here we summarise the current understanding of epigenetic changes that are associated with ADPKD, with a particular focus on the burgeoning field of ADPKD-specific alterations in DNA methylation.

High water vs. ad libitum water intake for autosomal dominant polycystic kidney disease: a randomized controlled feasibility trial

BACKGROUND

Vasopressin stimulates cyst growth in autosomal dominant polycystic kidney disease (ADPKD) and is a key therapeutic target. Evaluation of high water intake as an alternative to pharmacological vasopressin blockade is supported by patients. However feasibility, safety and adherence-promoting strategies required to deliver this remain unknown.

AIMS

Assess the feasibility of a definitive randomized high water intake trial in ADPKD.

METHODS

In this prospective open-label randomized trial, adult ADPKD patients with eGFR ≥ 20 ml/min/1.73 m2 were randomized to prescribed high water (HW) intake targeting urine osmolality (UOsm) ≤270 mOsm/kg, or ad libitum (AW) intake (UOsm >300 mOsm/kg). Self-management strategies including home-monitoring of urine-specific gravity (USG) were employed to promote adherence.

RESULTS

We enrolled 42 participants, baseline median eGFR (HW 68.4 [interquartile range (IQR) 35.9-107.2] vs. AW 75.8 [IQR 59.0-111.0 ml/min/1.73 m2, P = 0.22) and UOsm (HW 353 [IQR 190-438] vs. AW 350 [IQR 240-452] mOsm/kg, P = 0.71) were similar between groups. After 8 weeks, 67% in the HW vs. 24% in AW group achieved UOsm ≤270 mOsm/kg, P = 0.001. HW group achieved lower UOsm (194 [IQR 190-438] vs. 379 [IQR 235-503] mOsm/kg, P = 0.01) and higher urine volumes (3155 [IQR 2270-4295] vs. 1920 [IQR 1670-2960] ml/day, P = 0.02). Two cases of hyponatraemia occurred in HW group. No acute GFR effects were detected. In total 79% (519/672) of USG were submitted and 90% (468/519) were within target. Overall, 17% withdrew during the study.

CONCLUSION

DRINK demonstrated successful recruitment and adherence leading to separation between treatment arms in primary outcomes. These findings suggest a definitive trial assessing the impact of high water on kidney disease progression in ADPKD is feasible.

A high-throughput screening platform for Polycystic Kidney Disease (PKD) drug repurposing utilizing murine and human ADPKD cells

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited monogenic disorders, characterized by a progressive decline in kidney function due in part to the formation of fluid-filled cysts. While there is one FDA-approved therapy, it is associated with potential adverse effects, and all other clinical interventions are largely supportive. Insights into the cellular pathways underlying ADPKD have revealed striking similarities to cancer. Moreover, several drugs originally developed for cancer have shown to ameliorate cyst formation and disease progression in animal models of ADPKD. These observations prompted us to develop a high-throughput screening platform of cancer drugs in a quest to repurpose them for ADPKD. We screened ~8,000 compounds, including compounds with oncological annotations, as well as FDA-approved drugs, and identified 155 that reduced the viability of Pkd1-null mouse kidney cells with minimal effects on wild-type cells. We found that 109 of these compounds also reduced in vitro cyst growth of Pkd1-null cells cultured in a 3D matrix. Moreover, the result of the cyst assay identified therapeutically relevant compounds, including agents that interfere with tubulin dynamics and reduced cyst growth without affecting cell viability. Because it is known that several ADPKD therapies with promising outcomes in animal models failed to be translated to human disease, our platform also incorporated the evaluation of compounds in a panel of primary ADPKD and normal human kidney (NHK) epithelial cells. Although we observed differences in compound response amongst ADPKD and NHK cell preparation, we identified 18 compounds that preferentially affected the viability of most ADPKD cells with minimal effects on NHK cells. Our study identifies attractive candidates for future efficacy studies in advanced pre-clinical models of ADPKD.

Predictors of Hyperuricemia after Kidney Transplantation: Association with Graft Function

Background and objectives: In kidney transplant recipients (KTR), hyperuricemia (HU) is a commonly-observed phenomenon, due to calcineurin inhibitors and reduced kidney graft function. Factors predicting HU, and its association with graft function, remains equivocal. Materials and Methods: We conducted a retrospective longitudinal study to assess factors associated with HU in KTR, and to determine risk factors associated with graft function, measured as glomerular filtration rate (GFR). Moreover, GFR > 60 mL/min/1.73 m² was considered normal. HU was defined as a serum uric acid level of > 416 μmol/L (4.70 mg/dL) in men and >357 μmol/L (4.04 mg/dL) in women, or xanthine-oxidase inhibitor use. We built multiple logistic regression models to assess predictors of HU in KTR, as well as the association of demographic, clinical, and biochemical parameters of patients with normal GFR after a three-year follow-up. We investigated the effect modification of this association with HU. Results: There were 144 patients (mean age 46.6 ± 13.9), with 42.4% of them having HU. Predictors of HU in KTR were the presence of cystic diseases (OR = 9.68 (3.13; 29.9)), the use of diuretics (OR = 4.23 (1.51; 11.9)), and the male gender (OR = 2.45 (1.07; 5.56)). Being a younger age, of female gender, with a normal BMI, and the absence of diuretic medications increased the possibility of normal GFR. HU was the effect modifier of the association between demographic, clinical, and biochemical factors and a normal GFR. Conclusions: Factors associated with HU in KTR: Presence of cystic diseases, diuretic use, and male gender. HU was the effect modifier of the association of demographic, clinical, and biochemical factors to GFR.

The Role of Endothelin and Endothelin Antagonists in Chronic Kidney Disease

Background

Endothelins (ET) are a family of peptides that act as potent vasoconstrictors and pro-fibrotic growth factors. ET-1 is integral to renal and cardiovascular pathophysiology and exerts effects via autocrine, paracrine and endocrine signaling pathways tied to regulation of aldosterone, catecholamines, and angiotensin. In the kidney, ET-1 is critical to maintaining renal perfusion and controls glomerular arteriole tone and hemodynamics. It is hypothesized that ET-1 influences the progression of chronic kidney disease (CKD), and the objective of this review is to discuss the pathophysiology, and role of ET and endothelin receptor antagonists (ERAs) in CKD.

Summary

The use of ERAs in hypertensive nephropathy has the potential to decrease proteinuria, and in diabetic nephropathy has the potential to restore glycocalyx thickness, also decreasing proteinuria. Focal segmental glomerular sclerosis has no specific Food and Drug Administration-approved therapy currently, however, ERAs show promise in decreasing proteinuria and slowing tissue damage. ET-1 is a potential biomarker for autosomal dominant polycystic kidney disease progression and so it is thought that ERAs may be of some therapeutic benefit.

Key Messages

Multiple studies have shown the utility of ERAs in CKD. These agents have shown to reduce blood pressure, proteinuria, and arterial stiffness. However, more clinical trials are needed, and the results of active or recently concluded studies are eagerly awaited.

Inhibition of HDAC6 activity in kidney diseases: a new perspective

Histone deacetylase 6 (HDAC6), a cytoplasmic enzyme that plays important roles in many biological processes, is one isoform of a family of HDAC enzymes that catalyse the removal of functional acetyl groups from proteins. HDAC6 stands out from the other members of this family because it almost exclusively deacetylates cytoplasmic proteins and exerts deacetylation-independent effects, which has led to the successful development of relatively isoform-specific inhibitors of its enzymatic action. Numerous studies have recently demonstrated that HDAC6 expression and activity are increased in kidney disease, such as autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, and acute kidney injury (AKI), among others. Moreover, HDAC6 inhibitors have been investigated for use in treating these diseases. In fact, HDAC6 inhibitors effectively limit the progression of kidney diseases, suggesting that targeting HDAC6 may provide a novel treatment approach. However, the primary challenge in developing HDAC6-targeted therapies is understanding how the renoprotective effect of NDAC6 inhibitors can be selectively harnessed. Here, we discuss the unique function of HDAC6 and recapitulate the alluring potential of its inhibitors in kidney diseases.

Is the light at the end of the tunnel nigh? A review of ADPKD focusing on the burden of disease and tolvaptan as a new treatment

Autosomal dominant polycystic kidney disease (ADPKD) causes pathological cystic changes to the kidney and is characterized by numerous renal and systemic manifestations. ADPKD is the fourth most common renal disease requiring renal replacement therapy. In this report, we present a detailed review of ADPKD, with a particular focus on its major economic, psychological, and social burden in affected patients. Treatment of this disease has been based on prophylactic and supportive measures. However, in recent years, new drugs have emerged as promising agents that may retard the progression of ADPKD, such as tolvaptan. In this report, we provide an in-depth discussion of tolvaptan, which has shown an effect in decreasing annual total kidney volume growth and renal function decline, thus slowing disease progression. The mechanism of action, side effects, and available data on cost-effectiveness are discussed together with the results of the first clinical trials and the most recent trials with regard to its efficacy and safety. Tolvaptan has recently received approval and been granted marketing authorization in Japan, Canada, Korea, Switzerland, and Europe. A demand for widely accepted guidelines for its use has emerged since its approval. The currently available series of recommendations and guidelines as to when to start treatment with tolvaptan, as well as which patients should be treated, are also reviewed in this report. We lastly offer some considerations for future trials, and raise unanswered questions.

Urinary proteomics using capillary electrophoresis coupled to mass spectrometry for diagnosis and prognosis in kidney diseases

PURPOSE OF REVIEW

Urine is the most useful of body fluids for biomarker research. Therefore, we have focused on urinary proteomics, using capillary electrophoresis coupled to mass spectrometry, to investigate kidney diseases in recent years.

RECENT FINDINGS

Several urinary proteomics studies for the detection of various kidney diseases have indicated the potential of this approach aimed at diagnostic and prognostic assessment. Urinary protein biomarkers such as collagen fragments, serum albumin, α-1-antitrypsin, and uromodulin can help to explain the processes involved during disease progression.

SUMMARY

Urinary proteomics has been used in several studies in order to identify and validate biomarkers associated with different kidney diseases. These biomarkers, with improved sensitivity and specificity when compared with the current gold standards, provide a significant alternative for diagnosis and prognosis, as well as improving clinical decision-making.

Histone deacetylase 6 inhibition reduces cysts by decreasing cAMP and Ca2+ in knock-out mouse models of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is associated with progressive enlargement of multiple renal cysts, often leading to renal failure that cannot be prevented by a current treatment. Two proteins encoded by two genes are associated with ADPKD: PC1 (pkd1), primarily a signaling molecule, and PC2 (pkd2), a Ca²⁺ channel. Dysregulation of cAMP signaling is central to ADPKD, but the molecular mechanism is unresolved. Here, we studied the role of histone deacetylase 6 (HDAC6) in regulating cyst growth to test the possibility that inhibiting HDAC6 might help manage ADPKD. Chemical inhibition of HDAC6 reduced cyst growth in PC1-knock-out mice. In proximal tubule-derived, PC1-knock-out cells, adenylyl cyclase 6 and 3 (AC6 and -3) are both expressed. AC6 protein expression was higher in cells lacking PC1, compared with control cells containing PC1. Intracellular Ca²⁺ was higher in PC1-knock-out cells than in control cells. HDAC inhibition caused a drop in intracellular Ca²⁺ and increased ATP-simulated Ca²⁺ release. HDAC6 inhibition reduced the release of Ca²⁺ from the endoplasmic reticulum induced by thapsigargin, an inhibitor of endoplasmic reticulum Ca²⁺-ATPase. HDAC6 inhibition and treatment of cells with the intracellular Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) reduced cAMP levels in PC1-knock-out cells. Finally, the calmodulin inhibitors W-7 and W-13 reduced cAMP levels, and W-7 reduced cyst growth, suggesting that AC3 is involved in cyst growth regulated by HDAC6. We conclude that HDAC6 inhibition reduces cell growth primarily by reducing intracellular cAMP and Ca²⁺ levels. Our results provide potential therapeutic targets that may be useful as treatments for ADPKD.

Polycystin and calcium signaling in cell death and survival

Mutations in polycystin-1 (PC1) and polycystin-2 (PC2) result in a commonly occurring genetic disorder, called Autosomal Dominant Polycystic Kidney Disease (ADPKD), that is characterized by the formation and development of kidney cysts. Epithelial cells with loss-of-function of PC1 or PC2 show higher rates of proliferation and apoptosis and reduced autophagy. PC1 is a large multifunctional transmembrane protein that serves as a sensor that is usually found in complex with PC2, a calcium (Ca²⁺)-permeable cation channel. In addition to decreased Ca²⁺ signaling, several other cell fate-related pathways are de-regulated in ADPKD, including cAMP, MAPK, Wnt, JAK-STAT, Hippo, Src, and mTOR. In this review we discuss how polycystins regulate cell death and survival, highlighting the complexity of molecular cascades that are involved in ADPKD.

Safety and tolerability of autologous bone marrow mesenchymal stromal cells in ADPKD patients

Background

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic ciliopathy disease characterized by progressive formation and enlargement of cysts in multiple organs. The kidneys are particularly affected and patients may eventually develop end-stage renal disease (ESRD). We hypothesize that bone marrow mesenchymal stromal cells (BMMSCs) are renotropic and may improve kidney function via anti-apoptotic, anti-fibrotic, and anti-inflammatory effects. In this study, we aim to assess the safety and tolerability of a BMMSC infusion in ADPKD patients.

Methods

We performed a single-arm phase I clinical trial with a 12-month follow-up. This study enrolled six eligible ADPKD patients with an estimated glomerular filtration rate (eGFR) of 25–60 ml/min/1.73 m². Patients received autologous cultured BMMSCs (2 × 10⁶ cells/kg) through the cubital vein according to our infusion protocol. We investigated safety issues and kidney function during the follow-up visits, and compared the findings to baseline and 1 year prior to the intervention.

Results

There were no patients lost to follow-up. We observed no cell-related adverse events (AE) and serious adverse events (SAE) after 12 months of follow-up. The mean eGFR value of 33.8 ± 5.3 ml/min/1.73 m² 1 year before cell infusion declined to 26.7 ± 3.1 ml/min/1.73 m² at baseline (P = 0.03) and 25.8 ± 6.2 ml/min/1.73 m² at the 12-month follow-up visit (P = 0.62). The mean serum creatinine (SCr) level of 2 ± 0.3 mg/dl 1 year before the infusion increased to 2.5 ± 0.4 mg/dl at baseline (P = 0.04) and 2.5 ± 0.6 mg/dl at the 12-month follow-up (P = 0.96). This indicated significant changes between the differences of these two periods (12 months before infusion to baseline, and 12 months after infusion to baseline) in SCr (P = 0.05), but not eGFR (P = 0.09).

Conclusions

This trial demonstrated the safety and tolerability of an intravenous transplantation of autologous BMMSCs. BMMSC efficacy in ADPKD patients should be investigated in a randomized placebo-controlled trial with a larger population, which we intend to perform.

Trial registration

ClinicalTrials.gov, NCT02166489. Registered on June 14, 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0557-7) contains supplementary material, which is available to authorized users.

Autosomal dominant polycystic kidney disease: recent advances in clinical management

The first clinical descriptions of autosomal dominant polycystic kidney disease (ADPKD) go back at least 500 years to the late 16 (th) century. Advances in understanding disease presentation and pathophysiology have mirrored the progress of clinical medicine in anatomy, pathology, physiology, cell biology, and genetics. The identification of PKD1 and PKD2, the major genes mutated in ADPKD, has stimulated major advances, which in turn have led to the first approved drug for this disorder and a fresh reassessment of patient management in the 21 (st) century. In this commentary, we consider how clinical management is likely to change in the coming decade.

Relationship of urinary endothelin-1 with estimated glomerular filtration rate in autosomal dominant polycystic kidney disease: a pilot cross-sectional analysis

Background

The pathogenesis of progressive renal insufficiency in autosomal dominant polycystic kidney disease (ADPKD) is unclear. Evidence from experimental models of ADPKD suggests that elevated endothelin-1 (ET-1) drives cyst growth, renal fibrosis and loss of renal function, but whether ET-1 is elevated in humans with ADPKD is uncertain.

Methods

In a cross-sectional study of ADPKD we measured urinary ET-1, a surrogate for ET-1 in kidney cortex, in spot collections corrected for creatinine. The volume of each kidney was measured using MRI-based stereology. The relationship of urine ET-1 with MDRD eGFR and kidney volume was modeled by multiple linear regression with adjustment for clinical covariates.

Results

Patients with ADPKD were ages 18 to 53 with eGFRs (median, interquartile range) of 63.2 (43.5–80.2) ml/min/1.73 m² and albumin/creatinine ratios (ACR) of 115.0 (7.5–58.5) μg/mg. Urine ET-1 was inversely associated with eGFR (r = −0.480, P < 0.05) and positively (r = 0.407, P = 0.066) with ACR independent of age and female sex (P < 0.01). ET-1 appeared to be positively associated with total kidney volume (r = 0.426, P = 0.100), with a test for trend across urine ET-1 quartiles yielding z = 1.83, P = 0.068. ET-1 strongly correlated with NAGase (r = 0. 687, P = 0.001), a marker of tubular damage and a surrogate marker of renal disease progression in ADPKD. Of note, ET-1 levels in urine were not correlated with hypertension.

Conclusions

In a translational study of patients with ADPKD, urinary ET-1 was inversely associated with eGFR and positively correlated with total kidney volume. Taken together with results from experimental models, these findings suggest that the role of ET-1 in ADPKD warrants further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0232-8) contains supplementary material, which is available to authorized users.

A polycystin-centric view of cyst formation and disease: the polycystins revisited

It is 20 years since the identification of PKD1, the major gene mutated in autosomal dominant polycystic kidney disease (ADPKD), followed closely by the cloning of PKD2. These major breakthroughs have led in turn to a period of intense investigation into the function of the two proteins encoded, polycystin-1 and polycystin-2, and how defects in either protein lead to cyst formation and nonrenal phenotypes. In this review, we summarize the major findings in this area and present a current model of how the polycystin proteins function in health and disease.

Glycogen synthase kinase-3β promotes cyst expansion in polycystic kidney disease

Polycystic kidney diseases (PKDs) are inherited disorders characterized by the formation of fluid filled renal cysts. Elevated cAMP levels in PKDs stimulate progressive cyst enlargement involving cell proliferation and transepithelial fluid secretion often leading to end stage renal disease. The glycogen synthase kinase-3 (GSK3) family of protein kinases consists of GSK3α and GSK3β isoforms and plays a crucial role in multiple cellular signaling pathways. We previously found that GSK3β, a regulator of cell proliferation, is also crucial for cAMP generation and vasopressin mediated urine concentration by the kidneys. However, the role of GSK3β in the pathogenesis of PKDs is not known. Here we found that GSK3β expression and activity were markedly up-regulated and associated with cyst-lining epithelia in the kidneys of mice and humans with PKD. Renal collecting duct specific gene knockout of GSK3β or pharmacological inhibition of GSK3 effectively slowed the progression of PKD in mouse models of autosomal recessive or autosomal dominant PKD. GSK3 inactivation inhibited cAMP generation and cell proliferation resulting in reduced cyst expansion, improved renal function and extended lifespan. GSK3β inhibition also reduced pERK, c-Myc and Cyclin-D1, known mitogens in proliferation of cystic epithelial cells. Thus, GSK3β plays a novel functional role in PKD pathophysiology and its inhibition may be therapeutically useful to slow cyst expansion and progression of PKD.

How simple are 'simple renal cysts'?

The increasing use of medical imaging as an investigative tool is leading to the incidental and frequent finding of renal cysts in the general population. The presence of a solitary or multiple renal cysts has been generally considered benign in the absence of a family history of renal cystic disease or evidence of chronic kidney disease. Nonetheless, a number of recent studies have questioned this consensus by reported associations with the development of hypertension or malignant change. For these reasons, some clinicians consider the presence of renal cysts to be a contraindication to kidney donation. The situation is complicated by the different usage of the term 'simple' by some radiologists (to indicate non-complex lesions) or nephrologists (to indicate age-related non-hereditary lesions). We propose that the term 'simple' be replaced with the morphological description, Stage I renal cyst (Bosniak Classification). The presence of a Stage I renal cyst should not preclude kidney donation. However, occult renal disease should be excluded and appropriate donor assessment performed.

Polycystic kidney disease and cancer after renal transplantation

Autosomal dominant polycystic kidney disease (ADPKD), the most common form of polycystic kidney disease (PKD), is a disorder with characteristics of neoplasia. However, it is not known whether renal transplant recipients with PKD have an increased risk of cancer. Data from the Scientific Registry of Transplant Recipients, which contains information on all solid organ transplant recipients in the United States, were linked to 15 population-based cancer registries in the United States. For PKD recipients, we compared overall cancer risk with that in the general population. We also compared cancer incidence in PKD versus non-PKD renal transplant recipients using Poisson regression, and we determined incidence rate ratios (IRRs) adjusted for age, sex, race/ethnicity, dialysis duration, and time since transplantation. The study included 10,166 kidney recipients with PKD and 107,339 without PKD. Cancer incidence in PKD recipients was 1233.6 per 100,000 person-years, 48% higher than expected in the general population (standardized incidence ratio, 1.48; 95% confidence interval [95% CI], 1.37 to 1.60), whereas cancer incidence in non-PKD recipients was 1119.1 per 100,000 person-years. The unadjusted incidence was higher in PKD than in non-PKD recipients (IRR, 1.10; 95% CI, 1.01 to 1.20). However, PKD recipients were older (median age at transplantation, 51 years versus 45 years for non-PKD recipients), and after multivariable adjustment, cancer incidence was lower in PKD recipients than in others (IRR, 0.84; 95% CI, 0.77 to 0.91). The reason for the lower cancer risk in PKD recipients is not known but may relate to biologic characteristics of ADPKD or to cancer risk behaviors associated with ADPKD.

Role of extracellular ATP and P2 receptor signaling in regulating renal cyst growth and interstitial inflammation in polycystic kidney disease

Polycystic kidney diseases (PKD) are a group of inherited ciliopathies in which the formation and growth of multiple cysts derived from the distal nephron and collecting duct leads to the disruption of normal kidney architecture, chronic interstitial inflammation/fibrosis and hypertension. Kidney failure is the most life-threatening complication of PKD, and is the consequence of cyst expansion, renal interstitial disease and loss of normal kidney tissue. Over the last decade, accumulating evidence suggests that the autocrine and paracrine effects of ATP (through its receptor family P2X and P2Y), could be detrimental for the progression of PKD. (2009). In vitro, ATP-P2 signaling promotes cystic epithelial cell proliferation, chloride-driven fluid secretion and apoptosis. Furthermore, dysfunction of the polycystin signal transduction pathways promotes the secretagogue activity of extracellular ATP by activating a calcium-activated chloride channel via purinergic receptors. Finally, ATP is a danger signal and could potentially contribute to interstitial inflammation associated with PKD. These data suggest that ATP-P2 signaling worsens the progression of cyst enlargement and interstitial inflammation in PKD.