Vasopressin directly regulates cyst growth in polycystic kidney disease

Additional renoprotective effect of the SGLT2 inhibitor dapagliflozin in a patient with ADPKD receiving tolvaptan treatment

Autosomal dominant polycystic kidney disease (ADPKD) is a major cause of end-stage kidney disease (ESKD). Vasopressin plays a pivotal role in ADPKD progression; therefore, the selective vasopressin V2 receptor antagonist tolvaptan is used as a key drug in the management of ADPKD. On the other hand, sodium-glucose cotransporter-2 inhibitors (SGLT2i), which may possibly stimulate vasopressin secretion due to the diuretic effect of the drug, have been shown to have both renal and cardioprotective effects in various populations, including those with non-diabetic chronic kidney disease. However, the effect of SGLT2i in patients with ADPKD have not been fully elucidated. Herein, we report the case of a patient with ADPKD on tolvaptan who was administered the SGLT2i dapagliflozin. The patient was a Japanese woman diagnosed with ADPKD at age 30. Despite the treatment with tolvaptan, eGFR was gradually declined from 79.8 to 50 ml/min/1.73 m2 in almost 5 years and 10 mg of dapagliflozin was initiated in the hope of renoprotective effects. Although a small increase in vasopressin levels was observed, eGFR decline rate was moderated after dapagliflozin initiation. This case suggested an additional renoprotective effect of dapagliflozin in patient with ADPKD receiving tolvaptan. Although there is no evidence about the renal protective effect of SGLT2i in patients with ADPKD, we hereby report a case successfully treated with dapagliflozin for approximately 2 years. Further research, including clinical trials, is needed to evaluate whether SGLT2i are effective in patients with ADPKD.

The Impact of Autosomal Dominant Polycystic Kidney Disease in Children: A Nephrological, Nutritional, and Psychological Point of View

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disorder characterized by the formation of numerous fluid-filled cysts in the kidneys, leading to progressive renal failure and various extrarenal complications, including hypertension. This review explores the genetic basis of ADPKD, including emerging evidence of epigenetic mechanisms in modulating gene expression and disease progression in ADPKD. Furthermore, it proposes to examine the pathological characteristics of this condition at the nephrological, cardiovascular, nutritional, and psychological levels, emphasizing that the follow-up of patients with ADPKD should be multidisciplinary from a young pediatric age.

Dapagliflozin administration for 1 year promoted kidney enlargement in patient with ADPKD

To date, there is insufficient evidence regarding use of sodium-glucose cotransporter-2 (SGLT2) inhibitors for patients with autosomal-dominant polycystic kidney disease (ADPKD), as such cases have been excluded from previous clinical trials exploring the kidney protection effects of such medications. Here, findings of an ADPKD patient who received dapagliflozin, a selective SGLT2 inhibitor, for 1 year are presented. A 38-year-old woman with a family history of ADPKD wished for treatment with dapagliflozin. After starting administration at 10 mg/day, total kidney volume (TKV) continued to increase, from 1641 to 1764 mL after 84 days and then to 2297 mL after 340 days. The estimated glomerular filtration rate (eGFR) was also decreased from 67.3 to 56.2 mL/min/1.73 m2, and then to 51.4 mL/min/1.73 m2 at those times. Immediately after discontinuation of dapagliflozin, TKV and eGFR were slightly improved to 2263 mL and 55.1 mL/min/1.73 m2, respectively. Following a review of basic research studies, we consider that increased intratubular urinary osmotic pressure, compensatory glucose reabsorption by sodium-glucose cotransporter-1 in the late proximal tubule, and hypertrophy shown in collected cells caused by increased vasopressin may be associated with ADPKD disease progression. Caution may be needed when administering dapagliflozin to patients with ADPKD.

Structural basis of tolvaptan binding to the vasopressin V2 receptor

The vasopressin V2 receptor (V2R) is a validated therapeutic target for autosomal dominant polycystic kidney disease (ADPKD), with tolvaptan being the first FDA-approved antagonist. Herein, we used Gaussian accelerated molecular dynamics simulations to investigate the spontaneous binding of tolvaptan to both active and inactive V2R conformations at the atomic-level. Overall, the binding process consists of two stages. Tolvaptan binds initially to extracellular loops 2 and 3 (ECL2/3) before overcoming an energy barrier to enter the pocket. Our simulations result highlighted key residues (e.g., R181, Y205, F287, F178) involved in this process, which were experimentally confirmed by site-directed mutagenesis. This work provides structural insights into tolvaptan-V2R interactions, potentially aiding the design of novel antagonists for V2R and other G protein-coupled receptors.

Mechanistic complement of autosomal dominant polycystic kidney disease: the role of aquaporins

Autosomal dominant polycystic kidney disease is a genetic kidney disease caused by mutations in the genes PKD1 or PKD2. Its course is characterized by the formation of progressively enlarged cysts in the renal tubules bilaterally. The basic genetic explanation for autosomal dominant polycystic kidney disease is the double-hit theory, and many of its mechanistic issues can be explained by the cilia doctrine. However, the precise molecular mechanisms underpinning this condition's occurrence are still not completely understood. Experimental evidence suggests that aquaporins, a class of transmembrane channel proteins, including aquaporin-1, aquaporin-2, aquaporin-3, and aquaporin-11, are involved in the mechanism of autosomal dominant polycystic kidney disease. Aquaporins are either a potential new target for the treatment of autosomal dominant polycystic kidney disease, and further study into the physiopathological role of aquaporins in autosomal dominant polycystic kidney disease will assist to clarify the disease's pathophysiology and increase the pool of potential treatment options. We primarily cover pertinent findings on aquaporins in autosomal dominant polycystic kidney disease in this review.

Computational drug discovery approaches identify mebendazole as a candidate treatment for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a rare genetic disorder characterised by numerous renal cysts, the progressive expansion of which can impact kidney function and lead eventually to renal failure. Tolvaptan is the only disease-modifying drug approved for the treatment of ADPKD, however its poor side effect and safety profile necessitates the need for the development of new therapeutics in this area. Using a combination of transcriptomic and machine learning computational drug discovery tools, we predicted that a number of existing drugs could have utility in the treatment of ADPKD, and subsequently validated several of these drug predictions in established models of disease. We determined that the anthelmintic mebendazole was a potent anti-cystic agent in human cellular and in vivo models of ADPKD, and is likely acting through the inhibition of microtubule polymerisation and protein kinase activity. These findings demonstrate the utility of combining computational approaches to identify and understand potential new treatments for traditionally underserved rare diseases.

Cross-Species Insights into Autosomal Dominant Polycystic Kidney Disease: Provide an Alternative View on Research Advancement

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a prevalent hereditary disorder that affects the kidneys, characterized by the development of an excessive number of fluid-filled cysts of varying sizes in both kidneys. Along with the progression of ADPKD, these enlarged cysts displace normal kidney tissue, often accompanied by interstitial fibrosis and inflammation, and significantly impair renal function, leading to end-stage renal disease. Currently, the precise mechanisms underlying ADPKD remain elusive, and a definitive cure has yet to be discovered. This review delineates the epidemiology, pathological features, and clinical diagnostics of ADPKD or ADPKD-like disease across human populations, as well as companion animals and other domesticated species. A light has been shed on pivotal genes and biological pathways essential for preventing and managing ADPKD, which underscores the importance of cross-species research in addressing this complex condition. Treatment options are currently limited to Tolvaptan, dialysis, or surgical excision of large cysts. However, comparative studies of ADPKD across different species hold promise for unveiling novel insights and therapeutic strategies to combat this disease.

The screening, diagnosis, and management of patients with autosomal dominant polycystic kidney disease: A national consensus statement from Taiwan

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of end-stage kidney disease (ESKD) worldwide. Guidelines for the diagnosis and management of ADPKD in Taiwan remains unavailable. In this consensus statement, we summarize updated information on clinical features of international and domestic patients with ADPKD, followed by suggestions for optimal diagnosis and care in Taiwan. Specifically, counselling for at-risk minors and reproductive issues can be important, including ethical dilemmas surrounding prenatal diagnosis and pre-implantation genetic diagnosis. Studies reveal that ADPKD typically remains asymptomatic until the fourth decade of life, with symptoms resulting from cystic expansion with visceral compression, or rupture. The diagnosis can be made based on a detailed family history, followed by imaging studies (ultrasound, computed tomography, or magnetic resonance imaging). Genetic testing is reserved for atypical cases mostly. Common tools for prognosis prediction include total kidney volume, Mayo classification and PROPKD/genetic score. Screening and management of complications such as hypertension, proteinuria, urological infections, intracranial aneurysms, are also crucial for improving outcome. We suggest that the optimal management strategies of patients with ADPKD include general medical care, dietary recommendations and ADPKD-specific treatments. Key points include rigorous blood pressure control, dietary sodium restriction and Tolvaptan use, whereas the evidence for somatostatin analogues and mammalian target of rapamycin (mTOR) inhibitors remains limited. In summary, we outline an individualized care plan emphasizing careful monitoring of disease progression and highlight the need for shared decision-making among these patients.

Long-Residence Time Peptide Antagonist for the Vasopressin V2 Receptor to Treat Autosomal Dominant Polycystic Kidney Disease

The dysregulated intracellular cAMP in the kidneys drives cystogenesis and progression in autosomal dominant polycystic kidney disease (ADPKD). Mounting evidence supports that vasopressin V2 receptor (V2R) antagonism effectively reduces cAMP levels, validating this receptor as a therapeutic target. Tolvaptan, an FDA-approved V2R antagonist, shows limitations in its clinical efficacy for ADPKD treatment. Therefore, the pursuit of better-in-class V2R antagonists with an improved efficacy remains pressing. Herein, we synthesized a set of peptide V2R antagonists. Peptide 33 exhibited a high binding affinity for the V2R (Ki = 6.1 ± 1.5 nM) and an extended residence time of 20 ± 1 min, 2-fold that of tolvaptan. This prolonged interaction translated into sustained suppression of cAMP production in washout experiments. Furthermore, peptide 33 exhibited improved efficacies over tolvaptan in both ex vivo and in vivo models of ADPKD, underscoring its potential as a promising lead compound for the treatment of ADPKD.

Effects of salt and protein intake on polyuria in V2RA-treated ADPKD patients

BACKGROUND

The only treatment proven to be renoprotective in autosomal dominant polycystic kidney disease (ADPKD) is a vasopressin V2-receptor antagonist (V2RA). However, aquaresis-associated side effects limit tolerability. We investigated whether salt and/or protein intake influences urine volume and related endpoints in V2RA-treated ADPKD patients.

METHODS

In this randomized, controlled, double-blind, crossover trial, ADPKD patients treated with maximally tolerated dose of a V2RA were included. While on a low salt and low protein diet, patients were given additional salt and protein to mimic regular intake, which was subsequently replaced by placebo in random order during four 2-week periods. Primary endpoint was change in 24-h urine volume. Secondary endpoints were change in quality of life, measured glomerular filtration rate (mGFR), blood pressure and copeptin level.

RESULTS

Twelve patients (49 ± 8 years, 25.0% male) were included. Baseline salt and protein intake were 10.8 ± 1.3 g/24-h and 1.2 ± 0.2 g/kg/24-h, respectively. During the low salt and low protein treatment periods, intake decreased to 5.8 ± 1.6 g/24-h and 0.8 ± 0.1 g/kg/24-h, respectively. Baseline 24-h urine volume (5.9 ± 1.2 L) decreased to 5.2 ± 1.1 L (-11%, P = .004) on low salt and low protein, and to 5.4 ± 0.9 L (-8%, P = .04) on low salt. Reduction in 24-h urine volume was two times greater in patients with lower urine osmolality (-16% vs -7%). Polyuria quality of life scores improved in concordance with changes in urine volume. mGFR decreased during the low salt and low protein, while mean arterial pressure did not change during study periods. Plasma copeptin decreased significantly during low salt and low protein periods.

CONCLUSION

Lowering dietary salt and protein intake has a minor effect on urine volume in V2RA-treated ADPKD patients. Reduced intake of osmoles decreased copeptin concentrations and might thus increase the renoprotective effect of a V2RA in ADPKD patients.

Predicting autosomal dominant polycystic kidney disease progression: review of promising Serum and urine biomarkers

Autosomal dominant polycystic kidney disease (ADPKD) is one of the leading causes of end-stage renal disease. In spite of the recent tremendous progress in the understanding of ADPKD pathogenesis, the molecular mechanisms of the disease remain incompletely understood. Considering emerging new targeted therapies for ADPKD, it has become crucial to disclose easily measurable and widely available biomarkers for identifying patients with future rapid disease progression. This review encompasses all the research with a shared goal of identifying promising serum or urine biomarkers for predicting ADPKD progression or response to therapy. The rate of the ADPKD progress varies significantly between patients. The phenotypic variability is only partly explained by the underlying genetic lesion diversity. Considering significant decline in kidney function in ADPKD is not usually evident until at least 50% of the parenchyma has been destroyed, conventional kidney function measures, such as glomerular filtration rate (GFR), are not suitable for monitoring disease progression in ADPKD, particularly in its early stages. Since polycystic kidney enlargement usually precedes the decline in GFR, height-adjusted total kidney volume (ht-TKV) has been accepted as an early biomarker for assessing disease severity in ADPKD patients. However, since measuring ht-TKV is time-consuming and observer-dependent, the identification of a sensitive and quickly measurable biomarker is of a great interest for everyday clinical practice. Throughout the last decade, due to development of proteomic and metabolomic techniques and the enlightenment of multiple molecular pathways involved in the ADPKD pathogenesis, a number of urine and serum protein biomarkers have been investigated in ADPKD patients, some of which seem worth of further exploring. These include copeptin, angiotensinogen, monocyte chemoattractant protein 1, kidney injury molecule-1 and urine-to-plasma urea ratio among many others. The aim of the current review is to provide an overview of all of the published evidence on potentially clinically valuable serum and urine biomarkers that could be used for predicting disease progression or response to therapy in patients with ADPKD. Hopefully, this review will encourage future longitudinal prospective clinical studies evaluating proposed biomarkers as prognostic tools to improve management and outcome of ADPKD patients in everyday clinical practice.

The safety and efficacy of tolvaptan in the treatment of patients with autosomal dominant polycystic kidney disease: A systematic review and meta-analysis

BACKGROUND

The irreversible progression of autosomal dominant polycystic kidney disease (ADPKD) to end-stage renal disease (ESRD) is delayed by tolvaptan. Therefore, we aim to systematically estimate and evaluate the efficacy and safety of tolvaptan in the treatment of ADPKD.

METHODS

Two reviewers independently searched all published randomized controlled trials studies in PubMed, EMBASE, Web of Science and Cochrane databases, extracted data, assessed bias risk and rated the quality of evidence. Data were analyzed by the RevMan software.

RESULTS

We identified 8 trials including 2135 patients. Both of the decline of estimated glomerular filtration rate (eGFR) [MD=1.89, 95% CI (0.74, 3.04), P=0.001] and total kidney volume (TKV) [MD=-3.32, 95% CI (-4.57, -2.07), P<0.001] were delayed in tolvaptan group compared with placebo group in ADPKD patients. The use of tolvaptan delayed TKV progression in the different-month subgroups [MD=-69.99, 95% CI (-91.05, -48.94), P<0.001]. Tolvaptan reduced renal pain [RR=0.66, 95% CI (0.54, 0.81), P<0.001] and hematuria events [RR=0.55, 95% CI (0.41, 0.74), P<0.001] in ADPKD patients. However, the prevalence of thirst [RR=2.75, 95% CI (2.34, 3.24), P<0.001] and nocturia events [RR=3.01, 95% CI (1.27, 7.11), P=0.01] were increased in tolvaptan group. There is no significant difference of hypertension events [RR=0.92, 95% CI (0.82, 1.03), P=0.13] in tolvaptan group compared placebo group.

CONCLUSIONS

This meta-analysis suggests that tolvaptan may improve clinical progression in patients with ADPKD without significantly increasing the risk of adverse reactions.

Accelerated cystogenesis by dietary protein load is dependent on, but not initiated by kidney macrophages

Background

Disease severity of autosomal dominant polycystic kidney disease (ADPKD) is influenced by diet. Dietary protein, a recognized cyst-accelerating factor, is catabolized into amino acids (AA) and delivered to the kidney leading to renal hypertrophy. Injury-induced hypertrophic signaling in ADPKD results in increased macrophage (MФ) activation and inflammation followed by cyst growth. We hypothesize that the cystogenesis-prompting effects of HP diet are caused by increased delivery of specific AA to the kidney, ultimately stimulating MФs to promote cyst progression.

Methods

Pkd1flox/flox mice with and without Cre (CAGG-ER) were given tamoxifen to induce global gene deletion (Pkd1KO). Pkd1KO mice were fed either a low (LP; 6%), normal (NP; 18%), or high (HP; 60%) protein diet for 1 week (early) or 6 weeks (chronic). Mice were then euthanized and tissues were used for histology, immunofluorescence and various biochemical assays. One week fed kidney tissue was cell sorted to isolate tubular epithelial cells for RNA sequencing.

Results

Chronic dietary protein load in Pkd1KO mice increased kidney weight, number of kidney infiltrating and resident MФs, chemokines, cytokines and cystic index compared to LP diet fed mice. Accelerated cyst growth induced by chronic HP were attenuated by liposomal clodronate-mediated MФ depletion. Early HP diet fed Pkd1KO mice had larger cystic kidneys compared to NP or LP fed counterparts, but without increases in the number of kidney MФs, cytokines, or markers of tubular injury. RNA sequencing of tubular epithelial cells in HP compared to NP or LP diet group revealed increased expression of sodium-glutamine transporter Snat3, chloride channel Clcnka, and gluconeogenesis marker Pepck1, accompanied by increased excretion of urinary ammonia, a byproduct of glutamine. Early glutamine supplementation in Pkd1KO mice lead to kidney hypertrophy.

Conclusion

Chronic dietary protein load-induced renal hypertrophy and accelerated cyst growth in Pkd1KO mice is dependent on both infiltrating and resident MФ recruitment and subsequent inflammatory response. Early cyst expansion by HP diet, however, is relient on increased delivery of glutamine to kidney epithelial cells, driving downstream metabolic changes prior to inflammatory provocation.

Drug repurposing in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease is characterized by progressive kidney cyst formation that leads to kidney failure. Tolvaptan, a vasopressin 2 receptor antagonist, is the only drug approved to treat patients with autosomal dominant polycystic kidney disease who have rapid disease progression. The use of tolvaptan is limited by reduced tolerability from aquaretic effects and potential hepatotoxicity. Thus, the search for more effective drugs to slow down the progression of autosomal dominant polycystic kidney disease is urgent and challenging. Drug repurposing is a strategy for identifying new clinical indications for approved or investigational medications. Drug repurposing is increasingly becoming an attractive proposition because of its cost-efficiency and time-efficiency and known pharmacokinetic and safety profiles. In this review, we focus on the repurposing approaches to identify suitable drug candidates to treat autosomal dominant polycystic kidney disease and prioritization and implementation of candidates with high probability of success. Identification of drug candidates through understanding of disease pathogenesis and signaling pathways is highlighted.

Efficacy and Safety of Tolvaptan for Patients With Autosomal Dominant Polycystic Kidney Disease in Real-world Practice: A Single Institution Retrospective Study

BACKGROUND/AIM

We evaluated the efficacy and safety of tolvaptan for autosomal dominant polycystic kidney disease (ADPKD) in real-world practice.

PATIENTS AND METHODS

We retrospectively reviewed the cases of 27 patients who had been diagnosed with ADPKD between January 2014 and December 2022. Among them, 14 patients received tolvaptan (60 mg/day; morning: 45 mg, night: 15 mg) after being admitted for 2 days. In the outpatient clinic, blood and urine samples were taken monthly.

RESULTS

The mean age, pretreatment estimated glomerular filtration rate (eGFR), treatment duration, and total kidney volume were 60 years, 45.6 ml/min/1.73 m2, 2.8 years, and 2,390 ml, respectively. One month later, the patients' renal dysfunction had worsened slightly, and their serum sodium concentrations had significantly increased. After one year, the mean reduction in the eGFR was -5.5 ml/min/1.73 m² Moreover, at 3 years the patients' renal function was stable. No hepatic dysfunction or electrolyte abnormalities were noted, although discontinuation occurred in two cases. Tolvaptan treatment is considered to be safe.

CONCLUSION

Tolvaptan was effective against ADPKD in a real-world setting. Moreover, the safety of tolvaptan was confirmed.

The role of copeptin in kidney disease

Copeptin is a 39-amino acid glycopeptide that is secreted equimolecularly with arginine-vasopressin (AVP) from the prepro-hormone AVP in the posterior pituitary. While AVP is a very unstable molecule and is accompanied by significant technical troubles in its quantification, copeptin is a stable and easily quantifiable molecule. For this reason, circulating copeptin is currently used as a surrogate for AVP in different pathological conditions, including renal diseases. In recent years it has been shown that copeptin is associated with an increased risk of developing chronic kidney disease in the general population. In addition, copeptin has also been associated with multiple renal diseases with relevant clinical consequences and potential therapeutic implications. In the present review, we update and summarize the clinical significance of copeptin as a surrogate marker for AVP concentrations in different kidney diseases, as well as in renal replacement therapy (hemodialysis and peritoneal dialysis) and renal transplantation.

Hyponatremia and Cancer: From Bedside to Benchside

Hyponatremia is the most common electrolyte disorder encountered in hospitalized patients. This applies also to cancer patients. Multiple causes can lead to hyponatremia, but most frequently this electrolyte disorder is due to the syndrome of inappropriate antidiuresis. In cancer patients, this syndrome is mostly secondary to ectopic secretion of arginine vasopressin by tumoral cells. In addition, several chemotherapeutic drugs induce the release of arginine vasopressin by the hypothalamus. There is evidence that hyponatremia is associated to a more negative outcome in several pathologies, including cancer. Many studies have demonstrated that in different cancer types, both progression-free survival and overall survival are negatively affected by hyponatremia, whereas the correction of serum [Na⁺] has a positive effect on patient outcome. In vitro studies have shown that cells grown in low [Na⁺] have a greater proliferation rate and motility, due to a dysregulation in intracellular signalling pathways. Noteworthy, vasopressin receptors antagonists, which were approved more than a decade ago for the treatment of euvolemic and hypervolemic hyponatremia, have shown unexpected antiproliferative effects. Because of this property, vaptans were also approved for the treatment of polycystic kidney disease. In vitro evidence indicated that this family of drugs effectively counteracts proliferation and invasivity of cancer cells, thus possibly opening a new scenario among the pharmacological strategies to treat cancer.

Design of two ongoing clinical trials of tolvaptan in the treatment of pediatric patients with autosomal recessive polycystic kidney disease

PURPOSE

Autosomal recessive polycystic kidney disease (ARPKD) is a hereditary condition characterized by massive kidney enlargement and developmental liver defects. Potential consequences during childhood include the need for kidney replacement therapy (KRT). We report the design of 2 ongoing clinical trials (Study 204, Study 307) to evaluate safety, tolerability, and efficacy of tolvaptan in children with ARPKD.

METHODS

Both trials are of multinational, multicenter, open-label design. Age range at enrollment is 28 days to < 12 weeks in Study 204 and 28 days to < 18 years in Study 307. Subjects in both studies must have a clinical diagnosis of ARPKD, and those in Study 204 must additionally have signs indicative of risk of rapid progression to KRT, namely, all of: nephromegaly, multiple kidney cysts or increased kidney echogenicity suggesting microcysts, and oligohydramnios or anhydramnios. Target enrollment is 20 subjects for Study 204 and ≥ 10 subjects for Study 307.

RESULTS

Follow-up is 24 months in Study 204 (with optional additional treatment up to 36 months) and 18 months in Study 307. Outcomes include safety, tolerability, change in kidney function, and percentage of subjects requiring KRT relative to historical data. Regular safety assessments monitor for possible adverse effects of treatment on parameters such as liver function, kidney function, fluid balance, electrolyte levels, and growth trajectory, with increased frequency of monitoring following tolvaptan initiation or dose escalation.

CONCLUSIONS

These trials will provide data on tolvaptan safety and efficacy in a population without disease-specific treatment options.

TRIAL REGISTRATION

Study 204: EudraCT 2020-005991-36; Study 307: EudraCT 2020-005992-10.

The "3Ds" of Growing Kidney Organoids: Advances in Nephron Development, Disease Modeling, and Drug Screening

A kidney organoid is a three-dimensional (3D) cellular aggregate grown from stem cells in vitro that undergoes self-organization, recapitulating aspects of normal renal development to produce nephron structures that resemble the native kidney organ. These miniature kidney-like structures can also be derived from primary patient cells and thus provide simplified context to observe how mutations in kidney-disease-associated genes affect organogenesis and physiological function. In the past several years, advances in kidney organoid technologies have achieved the formation of renal organoids with enhanced numbers of specialized cell types, less heterogeneity, and more architectural complexity. Microfluidic bioreactor culture devices, single-cell transcriptomics, and bioinformatic analyses have accelerated the development of more sophisticated renal organoids and tailored them to become increasingly amenable to high-throughput experimentation. However, many significant challenges remain in realizing the use of kidney organoids for renal replacement therapies. This review presents an overview of the renal organoid field and selected highlights of recent cutting-edge kidney organoid research with a focus on embryonic development, modeling renal disease, and personalized drug screening.

Review of the Use of Animal Models of Human Polycystic Kidney Disease for the Evaluation of Experimental Therapeutic Modalities

Autosomal dominant polycystic kidney disease, autosomal recessive polycystic kidney disease, and nephronophthisis are hereditary disorders with the occurrence of numerous cysts in both kidneys, often causing chronic and end-stage renal failure. Animal models have played an important role in recent advances in research not only on disease onset and progressive mechanisms but also on the development of therapeutic interventions. For a long time, spontaneous animal models have been used as the primary focus for human diseases; however, after the identification of the nucleotide sequence of the responsible genes, PKD1, PKD2, PKHD1, and NPHPs, various types of genetically modified models were developed by genetic and reproductive engineering techniques and played the leading role in the research field. In this review, we present murine models of hereditary renal cystic diseases, discussing their potential benefits in the development of therapeutic strategies.

SCF-SKP2 E3 ubiquitin ligase links mTORC1/ER stress/ISR with YAP activation in murine renal cystogenesis

The Hippo pathway nuclear effector Yes-associated protein (YAP) potentiates the progression of polycystic kidney disease (PKD) arising from ciliopathies. The mechanisms underlying the increase in YAP expression and transcriptional activity in PKD remain obscure. We observed that in kidneys from mice with juvenile cystic kidney (jck) ciliopathy, the aberrant hyperactivity of mechanistic target of rapamycin complex 1 (mTORC1), driven by ERK1/2 and PI3K/AKT cascades, induced ER proteotoxic stress. To reduce this stress by reprogramming translation, the protein kinase R-like ER kinase-eukaryotic initiation factor 2α (PERK/eIF2α) arm of the integrated stress response (ISR) was activated. PERK-mediated phosphorylation of eIF2α drove the selective translation of activating transcription factor 4 (ATF4), potentiating YAP expression. In parallel, YAP underwent K63-linked polyubiquitination by SCF S-phase kinase-associated protein 2 (SKP2) E3 ubiquitin ligase, a Hippo-independent, nonproteolytic ubiquitination that enhances YAP nuclear trafficking and transcriptional activity in cancer cells. Defective ISR cellular adaptation to ER stress in eIF2α phosphorylation-deficient jck mice further augmented YAP-mediated transcriptional activity and renal cyst growth. Conversely, pharmacological tuning down of ER stress/ISR activity and SKP2 expression in jck mice by administration of tauroursodeoxycholic acid (TUDCA) or tolvaptan impeded these processes. Restoring ER homeostasis and/or interfering with the SKP2-YAP interaction represent potential therapeutic avenues for stemming the progression of renal cystogenesis.

Expression of active B-Raf proto-oncogene in kidney collecting ducts induces cyst formation in normal mice and accelerates cyst growth in mice with polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by the formation and progressive enlargement of fluid-filled cysts due to abnormal cell proliferation. Cyclic AMP agonists, including arginine vasopressin, stimulate ERK-dependent proliferation of cystic cells, but not normal kidney cells. Previously, B-Raf proto-oncogene (BRAF), a MAPK kinase kinase that activates MEK-ERK signaling, was shown to be a central intermediate in the cAMP mitogenic response. However, the role of BRAF on cyst formation and enlargement in vivo had not been demonstrated. To determine if active BRAF induces kidney cyst formation, we generated transgenic mice that conditionally express BRAFV600E, a common activating mutation, and bred them with Pkhd1-Cre mice to express active BRAF in the collecting ducts, a predominant site for cyst formation. Collecting duct expression of BRAFV600E (BRafCD) caused kidney cyst formation as early as three weeks of age. There were increased levels of phosphorylated ERK (p-ERK) and proliferating cell nuclear antigen, a marker for cell proliferation. BRafCD mice developed extensive kidney fibrosis and elevated blood urea nitrogen, indicating a decline in kidney function, by ten weeks of age. BRAFV600E transgenic mice were also bred to Pkd1RC/RC and pcy/pcy mice, well-characterized slowly progressive PKD models. Collecting duct expression of active BRAF markedly increased kidney weight/body weight, cyst number and size, and total cystic area. There were increased p-ERK levels and proliferating cells, immune cell infiltration, interstitial fibrosis, and a decline in kidney function in both these models. Thus, our findings demonstrate that active BRAF is sufficient to induce kidney cyst formation in normal mice and accelerate cystic disease in PKD mice.

Adult human kidney organoids originate from CD24+ cells and represent an advanced model for adult polycystic kidney disease

Adult kidney organoids have been described as strictly tubular epithelia and termed tubuloids. While the cellular origin of tubuloids has remained elusive, here we report that they originate from a distinct CD24+ epithelial subpopulation. Long-term-cultured CD24+ cell-derived tubuloids represent a functional human kidney tubule. We show that kidney tubuloids can be used to model the most common inherited kidney disease, namely autosomal dominant polycystic kidney disease (ADPKD), reconstituting the phenotypic hallmark of this disease with cyst formation. Single-cell RNA sequencing of CRISPR-Cas9 gene-edited PKD1- and PKD2-knockout tubuloids and human ADPKD and control tissue shows similarities in upregulation of disease-driving genes. Furthermore, in a proof of concept, we demonstrate that tolvaptan, the only approved drug for ADPKD, has a significant effect on cyst size in tubuloids but no effect on a pluripotent stem cell-derived model. Thus, tubuloids are derived from a tubular epithelial subpopulation and represent an advanced system for ADPKD disease modeling.

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3',5'-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

The V2 receptor antagonist tolvaptan counteracts proliferation and invasivity in human cancer cells

PURPOSE

Hyponatremia, the most frequent electrolyte alteration in clinical practice, has been associated with a worse prognosis in cancer patients. On the other hand, a better outcome has been related to serum sodium normalization. In vitro studies have shown that low extracellular sodium promotes cancer cells proliferation and invasiveness. Tolvaptan, a selective vasopressin receptor type 2 (V₂) antagonist, has been effectively used in the last decade for the treatment of hyponatremia secondary to the Syndrome of Inappropriate Antidiuresis. A few in vitro data suggested a direct role of tolvaptan in counteracting cancer progression, so far. The aim of this study was to evaluate the effect and the mechanism of action of tolvaptan in cell lines from different tumours [i.e. colon cancer (HCT-8), hepatocarcinoma (HepG2), neuroblastoma (SK-N-AS)].

METHODS AND RESULTS

First, we showed that these cell lines express the V₂ receptor. Tolvaptan significantly reduced cell proliferation with an IC₅₀ in the micromolar range. Accordingly, reduced levels of cAMP, of the catalytic α subunit of PKA, and a reduced pAKT/AKT ratio were observed. Tolvaptan effectively inhibited cell cycle progression, whereas it induced apoptotis. Furthermore, it reduced cell invasiveness. In particular, anchorage-independent growth and the activity of collagenases type IV were blunted in the three cell lines. Accordingly, tolvaptan counteracted the RhoA/ROCK1-2 pathway, which has a pivotal role in regulating cell movement.

CONCLUSIONS

Overall, these findings indicate that tolvaptan effectively inhibits tumour progression in vitro. Further studies should clarify whether the V₂ receptor might be considered a possible target in anti-cancer strategies in the future.

dDAVP Downregulates the AQP3-Mediated Glycerol Transport via V1aR in Human Colon HCT8 Cells

Vasopressin (AVP) plays a key function in controlling body water and salt balance through the activation of the vasopressin receptors V1aR and V2R. Abnormal secretion of AVP can cause the syndrome of inappropriate antidiuresis that leads to hyponatremia, which is an electrolyte disorder often observed in the elderly hospitalized and oncologic patients. Beyond kidneys, the colonic epithelium modulates water and salt homeostasis. The water channel AQP3, expressed in villus epithelial cells is implicated in water absorption across human colonic surface cells. Here, the action of dDAVP, a stable vasopressin analog, was evaluated on the AQP3 expression and function using human colon HCT8 cells as an experimental model. Confocal and Western Blotting analysis revealed that HCT8 cells express both V1aR and V2R. Long-term (72 h) treatment with dDAVP reduced glycerol uptake and cell viability. These effects were prevented by SR49059, a synthetic antagonist of V1aR, but not by tolvaptan, a specific V2R antagonist. Of note, the SR49059 action was impaired by DFP00173, a selective inhibitor of AQP3. Interestingly, compared to the normal colonic mucosa, in the colon of patients with adenocarcinoma, the expression of V1aR was significantly decreased. These findings were confirmed by gene expression analysis with RNA-Seq data. Overall, data suggest that dDAVP, through the V1aR dependent pathway, reduces AQP3 mediated glycerol uptake, a process that is reversed in adenocarcinoma, suggesting that the AVP-dependent AQP3 pathway may represent a novel target in colon diseases associated with abnormal cell growth.

Comparative Efficacy of Pharmacological Treatments for Adults With Autosomal Dominant Polycystic Kidney Disease: A Systematic Review and Network Meta-Analysis of Randomized Controlled Trials

Background: Tolvaptan is the gold standard treatment for autosomal dominant polycystic kidney disease (ADPKD), while several other drugs have the potential to inhibit the progression of ADPKD. However, individual clinical trials may not show sufficient differences in clinical efficacy due to small sample sizes. Furthermore, the differences in therapeutic efficacy among drugs are unclear. Herein, we investigated the effect of the ADPKD treatments. Methods: We systematically searched PubMed, Medline, EMBASE, and the Cochrane Library through January 2022 to identify randomized controlled trials in ADPKD patients that compared the effects of treatments with placebo or conventional therapy. A network meta-analysis was performed to compare the treatments indirectly. The primary outcomes were changes in kidney function and the rate of total kidney volume (TKV) growth. Results: Sixteen studies were selected with a total of 4,391 patients. Tolvaptan significantly preserved kidney function and inhibited TKV growth compared to the placebo {standardized mean difference (SMD) [95% confidence interval (CI)]: 0.24 (0.16; 0.31) and MD: -2.70 (-3.10; -2.30), respectively}. Tyrosine kinase inhibitors and mammalian target of rapamycin (mTOR) inhibitors inhibited TKV growth compared to the placebo; somatostatin analogs significantly inhibited TKV growth compared to the placebo and tolvaptan [MD: -5.69 (-7.34; -4.03) and MD: -2.99 (-4.69; -1.29), respectively]. Metformin tended to preserve renal function, although it was not significant [SMD: 0.28 (-0.05; 0.61), p = 0.09]. Conclusion: The therapeutic effect of tolvaptan was reasonable as the gold standard for ADPKD treatment, while somatostatin analogs also showed notable efficacy in inhibiting TKV growth. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42022300814.

Benzodiazepine Derivatives as Potent Vasopressin V2 Receptor Antagonists for the Treatment of Autosomal Dominant Kidney Disease

Cyst formation and enlargement in autosomal dominant kidney disease (ADPKD) is mainly driven by aberrantly increased cytosolic cAMP in renal tubule epithelial cells. Because the vasopressin V₂ receptor (V₂R) regulates intracellular cAMP levels in kidneys, a series of benzodiazepine derivatives were developed targeting the V₂R. Among these derivatives, compound 25 exhibited potent binding affinity to the V₂R (K_i = 9.0 ± 1.5 nM) and efficacious cAMP inhibition (IC₅₀ = 9.2 ± 3.0 nM). This led to the suppression of cyst formation and growth in both an MDCK cell model and an embryonic kidney cyst model. Further advancing compound 25 in a murine model of ADPKD demonstrated a significantly improved in vivo efficacy compared with the reference compound tolvaptan. Overall, compound 25 holds therapeutic potential for the treatment of ADPKD.

Autosomal Dominant Polycystic Kidney Disease: From Pathophysiology of Cystogenesis to Advances in the Treatment

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, with an estimated prevalence between 1:1000 and 1:2500. It is mostly caused by mutations of the PKD1 and PKD2 genes encoding polycystin 1 (PC1) and polycystin 2 (PC2) that regulate cellular processes such as fluid transport, differentiation, proliferation, apoptosis and cell adhesion. Reduction of calcium ions and induction of cyclic adenosine monophosphate (sAMP) promote cyst enlargement by transepithelial fluid secretion and cell proliferation. Abnormal activation of MAPK/ERK pathway, dysregulated signaling of heterotrimeric G proteins, mTOR, phosphoinositide 3-kinase, AMPK, JAK/STAT activator of transcription and nuclear factor kB (NF-kB) are involved in cystogenesis. Another feature of cystic tissue is increased extracellular production and recruitment of inflammatory cells and abnormal connections among cells. Moreover, metabolic alterations in cystic cells including defective glucose metabolism, impaired beta-oxidation and abnormal mitochondrial activity were shown to be associated with cyst expansion. Although tolvaptan has been recently approved as a drug that slows ADPKD progression, some patients do not tolerate tolvaptan because of frequent aquaretic. The advances in the knowledge of multiple molecular pathways involved in cystogenesis led to the development of animal and cellular studies, followed by the development of several ongoing randomized controlled trials with promising drugs. Our review is aimed at pathophysiological mechanisms in cystogenesis in connection with the most promising drugs in animal and clinical studies.

Protein Kinase A Downregulation Delays the Development and Progression of Polycystic Kidney Disease

Background: Upregulation of cAMP-dependent and -independent PKA signaling is thought to promote cystogenesis in polycystic kidney disease (PKD). PKA-I regulatory subunit RIα is increased in kidneys of orthologous mouse models. Kidney-specific knockout of RIα upregulates PKA activity, induces cystic disease in wild-type mice, and aggravates it in Pkd1 ^RC/RC mice. Methods: PKA-I activation or inhibition was compared to EPAC activation or PKA-II inhibition using Pkd1 ^RC/RC metanephric organ cultures. The effect of constitutive PKA (preferentially PKA-I) downregulation in vivo was ascertained by kidney-specific expression of a dominant negative RIαB allele in Pkd1 ^RC/RC mice obtained by crossing Prkar1α ^R1αB/WT, Pkd1 ^RC/RC, and Pkhd1-Cre mice (C57BL/6 background). The effect of pharmacologic PKA inhibition using a novel, selective PRKACA inhibitor (BLU2864) was tested in mIMCD3 3D cultures, metanephric organ cultures, and Pkd1 ^RC/RC mice on a C57BL/6 x 129S6/Sv F1 background. Mice were sacrificed at 16 weeks of age. Results: PKA-I activation promoted and inhibition prevented ex vivo P-Ser133 CREB expression and cystogenesis. EPAC activation or PKA-II inhibition had no or only minor effects. BLU2864 inhibited in vitro mIMCD3 cystogenesis and ex vivo P-Ser133 CREB expression and cystogenesis. Genetic downregulation of PKA activity and BLU2864 directly and/or indirectly inhibited many pro-proliferative pathways and were both protective in vivo BLU2864 had no detectable on- or off-target adverse effects. Conclusions: PKA-I is the main PKA isozyme promoting cystogenesis. Direct PKA inhibition may be an effective strategy to treat PKD and other conditions where PKA signaling is upregulated. By acting directly on PKA, the inhibition may be more effective than or substantially increase the efficacy of treatments that only affect PKA activity by lowering cAMP.

Effects of Tolvaptan on Oxidative Stress in ADPKD: A Molecular Biological Approach

Autosomal dominant polycystic disease (ADPKD) is the most frequent monogenic kidney disease. It causes progressive renal failure, endothelial dysfunction, and hypertension, all of which are strictly linked to oxidative stress (OxSt). Treatment with tolvaptan is known to slow the renal deterioration rate, but not all the molecular mechanisms involved in this effect are well-established. We evaluated the OxSt state in untreated ADPKD patients compared to that in tolvaptan-treated ADPKD patients and healthy subjects. OxSt was assessed in nine patients for each group in terms of mononuclear cell p22^phox protein expression, NADPH oxidase key subunit, MYPT-1 phosphorylation state, marker of Rho kinase activity (Western blot) and heme oxygenase (HO)-1, induced and protective against OxSt (ELISA). p22^phox protein expression was higher in untreated ADPKD patients compared to treated patients and controls: 1.42 ± 0.11 vs. 0.86 ± 0.15 d.u., p = 0.015, vs. 0.53 ± 0.11 d.u., p < 0.001, respectively. The same was observed for phosphorylated MYPT-1: 0.96 ± 0.28 vs. 0.68 ± 0.09 d.u., p = 0.013 and vs. 0.47 ± 0.13 d.u., p < 0.001, respectively, while the HO-1 expression of untreated patients was significantly lower compared to that of treated patients and controls: 5.33 ± 3.34 vs. 2.08 ± 0.79 ng/mL, p = 0.012, vs. 1.97 ± 1.22 ng/mL, p = 0.012, respectively. Tolvaptan-treated ADPKD patients have reduced OxSt levels compared to untreated patients. This effect may contribute to the slowing of renal function loss observed with tolvaptan treatment.

Prescribed Water Intake in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND: Arginine vasopressin promotes kidney cyst growth in autosomal dominant polycystic kidney disease (ADPKD). Increased water intake reduces arginine vasopressin and urine osmolality and may slow kidney cyst growth. METHODS: In this randomized controlled 3-year clinical trial, we randomly assigned adults with ADPKD who had a height-corrected total kidney volume in Mayo imaging subclass categories 1B to 1E and an estimated glomerular filtration rate of 30 ml/min/1.73 m2 or greater to (1) water intake prescribed to reduce 24-hour urine osmolality to 270 mOsmol/kg or less or (2) ad libitum water intake irrespective of 24-hour urine osmolality. The primary end point was the percentage annualized rate of change in height-corrected total kidney volume. RESULTS: A total of 184 patients participated in either the ad libitum water intake group (n=92) or the prescribed water intake group (n=92). Over 3 years, there was no difference in the annualized rate of change in height-corrected total kidney volume between the ad libitum (7.8% per year; 95% confidence interval [CI], 6.6 to 9.0) and prescribed (6.8% per year; 95% CI, 5.8 to 7.7) water intake groups (mean difference, −0.97% per year; 95% CI, −2.37 to 0.44; P=0.18). The difference in mean 24-hour urine osmolality between the ad libitum and prescribed water intake groups was −91 mOsmol/kg (95% CI, −127 to −54 mOsmol/kg), with 52.3% of patients achieving adherence to the target 24-hour urine osmolality and no reduction in serum copeptin over 3 years. The frequency of adverse events was similar between groups. CONCLUSIONS: For patients with ADPKD, prescribed water intake was not associated with excess adverse events and achieved the target 24-hour urine osmolality for half of the patients but did not reduce copeptin or slow the growth of total kidney volume over 3 years compared with ad libitum water intake. (Funded by the National Health and Medical Research Council of Australia [grant GNT1138533], Danone Research, PKD Australia, the University of Sydney, and the Westmead Medical Research Foundation; Australian New Zealand Clinical Trials Registry number, ACTRN12614001216606).

Can Additional Water a Day Keep the Cysts Away, in Patients with Polycystic Kidney Disease?

Can Additional Water a Day Keep the Cysts Away, in Patients with Polycystic Kidney Disease? If a patient with autosomal dominant polycystic kidney disease could drink enough water to suppress arginine vasopressin release, would cyst growth be attenuated, thereby reducing the decline in kidney function over time? Louise M. Moist, M.D. discusses this randomized controlled trial.

Conformational selection of vasopressin upon V1a receptor binding

The neuropeptide vasopressin (VP) and its three G protein-coupled receptors (V_1aR, V_1bR and V₂R) are of high interest in a wide array of drug discovery programs. V_1aR is of particular importance due to its cardiovascular functions and diverse roles in the central nervous system. The structure–activity relationships underpinning ligand-receptor interactions remain however largely unclear, hindering rational drug design. This is not least due to the high structural flexibility of VP in its free as well as receptor-bound states. In this work, we developed a novel approach to reveal features of conformational selectivity upon VP-V_1aR complex formation. We employed virtual screening strategies to probe VP’s conformational space for transiently adopted structures that favor binding to V_1aR. To this end, we dissected the VP conformational space into three sub-ensembles, each containing distinct structural sets for VP’s three-residue C-terminal tail. We validated the computational results with experimental nuclear magnetic resonance (NMR) data and docked each sub-ensemble to V_1aR. We observed that the conformation of VP’s three-residue tail significantly modulated the complex dissociation constants. Solvent-exposed and proline trans-configured VP tail conformations bound to the receptor with three-fold enhanced affinities compared to compacted or cis-configured conformations. The solvent-exposed and more flexible structures facilitated unique interaction patterns between VP and V_1aR transmembrane helices 3, 4, and 6 which led to high binding energies. The presented “virtual conformational space screening” approach, integrated with NMR spectroscopy, thus enabled identification and characterization of a conformational selection-type complex formation mechanism that confers novel perspectives on targeting the VP-V_1aR interactions at the level of the encounter complex – an aspect that opens novel research avenues for understanding the functionality of the evolutionary selected conformational properties of VP, as well as guidance for ligand design strategies to provide more potent and selective VP analogues.

Retarding Progression of Chronic Kidney Disease in Autosomal Dominant Polycystic Kidney Disease with Metformin and Other Therapies: An Update of New Insights

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent single-gene disorder leading to renal failure. Current therapies are aimed to treat renal and extrarenal complications of ADPKD, but improved knowledge of the pathophysiological mechanisms leading to the generation and growth of cysts has permitted the identification of new drug candidates for clinical trials. Among these, in this review, we will examine above all the role of metformin, hypothesized to be able to activate the AMP-activated protein kinase (AMPK) pathway and potentially modulate some mechanisms implicated in the onset and the growth of the cysts.

Predictors of progression in autosomal dominant and autosomal recessive polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are characterized by bilateral cystic kidney disease leading to progressive kidney function decline. These diseases also have distinct liver manifestations. The range of clinical presentation and severity of both ADPKD and ARPKD is much wider than was once recognized. Pediatric and adult nephrologists are likely to care for individuals with both diseases in their lifetimes. This article will review genetic, clinical, and imaging predictors of kidney and liver disease progression in ADPKD and ARPKD and will briefly summarize pharmacologic therapies to prevent progression.

Safety Profile of Tolvaptan in the Treatment of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease constitutes the most prevalent hereditary kidney disease, associated with high rates of morbidity leading eventually to end-stage renal disease. Tolvaptan is a selective vasopressin antagonist and has emerged as a promising therapeutic option for patients with autosomal dominant polycystic kidney disease. The present review summarized current evidence regarding the safety profile of tolvaptan in patients with the disease. Consistent with its pharmacological action, aquaretic adverse events represent the most common side effects of tolvaptan, consisting of polyuria, pollakiuria and polydipsia. Gradual dose titration based on urinary osmolality, as well as dietary interventions aiming to reduce solute excretion, have been proposed as potential strategies to mitigate polyuria. In addition, tolvaptan administration may be complicated by liver injury, characterized by alanine aminotransferase and bilirubin elevations. Hepatotoxicity has been suggested to be triggered by impaired biliary clearance, activation of innate immunity and increased oxidative stress. Frequent monitoring of liver function tests has been shown to be effective in preventing Hy’s Law and liver failure cases. Uric acid elevation due to reduced renal excretion may lead to hyperuricemia and gout, although no drug discontinuations have been linked to these events. Future studies should confirm the safety profile of tolvaptan in large-scale real-world studies, clarify the pathogenetic pathways leading to hepatotoxicity and define its role in special populations, especially pediatric patients.

The cellular pathways and potential therapeutics of Polycystic Kidney Disease

Polycystic Kidney Disease (PKD) refers to a group of disorders, driven by the formation of cysts in renal tubular cells and is currently one of the leading causes of end-stage renal disease. The range of symptoms observed in PKD is due to mutations in cilia-localising genes, resulting in changes in cellular signalling. As such, compounds that are currently in preclinical and clinical trials target some of these signalling pathways that are dysregulated in PKD. In this review, we highlight these pathways including cAMP, EGF and AMPK signalling and drugs that target them and may show promise in lessening the disease burden of PKD patients. At present, tolvaptan is the only approved therapy for ADPKD, however, it carries several adverse side effects whilst comparatively, no pharmacological drug is approved for ARPKD treatment. Aside from this, drugs that have been the subject of multiple clinical trials such as metformin, which targets AMPK signalling and somatostatins, which target cAMP signalling have shown great promise in reducing cyst formation and cellular proliferation. This review also discusses other potential and novel targets that can be used for future interventions, such as β-catenin and TAZ, where research has shown that a reduction in the overexpression of these signalling components results in amelioration of disease phenotype. Thus, it becomes apparent that well-designed preclinical investigations and future clinical trials into these pathways and other potential signalling targets are crucial in bettering disease prognosis for PKD patients and could lead to personalised therapy approaches.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare disorder and one of the most severe forms of polycystic kidney disease, leading to end-stage renal disease (ESRD) in childhood. PKHD1 is the gene that is responsible for the vast majority of ARPKD. However, some cases have been related to a new gene that was recently identified (DZIP1L gene), as well as several ciliary genes that can mimic a ARPKD-like phenotypic spectrum. In addition, a number of molecular pathways involved in the ARPKD pathogenesis and progression were elucidated using cellular and animal models. However, the function of the ARPKD proteins and the molecular mechanism of the disease currently remain incompletely understood. Here, we review the clinics, treatment, genetics, and molecular basis of ARPKD, highlighting the most recent findings in the field.

Human reconstructed kidney models

The human kidney, which consists of up to 2 million nephrons, is critical for blood filtration, electrolyte balance, pH regulation, and fluid balance in the body. Animal experiments, particularly mice and rats, combined with advances in genetically modified technology have been the primary mechanism to study kidney injury in recent years. Mouse or rat kidneys, however, differ substantially from human kidneys at the anatomical, histological, and molecular levels. These differences combined with increased regulatory hurdles and shifting attitudes towards animal testing by non-specialists have led scientists to develop new and more relevant models of kidney injury. Although in vitro tissue culture studies are a valuable tool to study kidney injury and have yielded a great deal of insight, they are not a perfect model. Perhaps, the biggest limitation of tissue culture is that it cannot replicate the complex architecture, consisting of multiple cell types, of the kidney, and the interplay between these cells. Recent studies have found that pluripotent stem cells (PSCs), which are capable of differentiation into any cell type, can be used to generate kidney organoids. Organoids recapitulate the multicellular relationships and microenvironments of complex organs like kidney. Kidney organoids have been used to successfully model nephrotoxin-induced tubular and glomerular disease as well as complex diseases such as chronic kidney disease (CKD), which involves multiple cell types. In combination with genetic engineering techniques, such as CRISPR-Cas9, genetic diseases of the kidney can be reproduced in organoids. Thus, organoid models have the potential to predict drug toxicity and enhance drug discovery for human disease more accurately than animal models.

Per-Treatment Post Hoc Analysis of Clinical Trial Outcomes With Tolvaptan in ADPKD

Introduction

In pivotal trials of patients with autosomal dominant polycystic kidney disease at risk of rapid progression, tolvaptan slowed estimated glomerular filtration rate (eGFR) decline in early-to-moderate (TEMPO 3:4 [NCT00428948]) and moderate- to late-stage (REPRISE [NCT02160145]) chronic kidney disease (CKD). Discontinuation was less frequent in REPRISE (15.0%) than TEMPO 3:4 (23.0%), given that in REPRISE, only subjects who tolerated tolvaptan 60/30 mg daily initiated the double-blind phase. We evaluated whether the greater treatment effect in REPRISE was attributable to different completion rates.

Methods

We conducted post hoc analyses of TEMPO 3:4 and REPRISE completers, defined as subjects who took trial drug to the end of the treatment period in TEMPO 3:4 (3 years) or REPRISE (1 year). Efficacy (rate of change in eGFR for tolvaptan vs. placebo) was analyzed as in each trial. Subjects from TEMPO 3:4 and REPRISE were also matched by propensity score for age, gender, and baseline eGFR to explore potential additional determinants of treatment effect.

Results

The annualized tolvaptan treatment effect in TEMPO 3:4 completers (difference vs. placebo of 0.98 ml/min per 1.73 m²/y) and REPRISE completers (difference of 1.23) was similar to that of the respective total trial populations (TEMPO 3:4: 0.94; REPRISE: 1.27). The treatment effect of tolvaptan was also similar between matched subjects.

Conclusion

Greater treatment completion rate did not drive greater treatment effect in REPRISE. The more advanced CKD of REPRISE subjects may be more relevant. More rapid decline in kidney function in later-stage CKD enabled the effects of tolvaptan to be more easily discerned.

Preservation of kidney function irrelevant of total kidney volume growth rate with tolvaptan treatment in patients with autosomal dominant polycystic kidney disease

Background

Tolvaptan slowed the rates of total kidney volume (TKV) growth and renal function decline over a 3-year period in patients with autosomal dominant polycystic kidney disease (ADPKD) enrolled in the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4 trial (NCT00428948). In this post hoc analysis of Japanese patients from TEMPO 3:4, we evaluated whether the effects of tolvaptan on TKV and on renal function are interrelated.

Methods

One hundred and forty-seven Japanese patients from TEMPO 3:4 were included in this analysis (placebo, n = 55; tolvaptan, n = 92). Tolvaptan-treated patients were stratified into the responder group (n = 37), defined as tolvaptan-treated patients with a net decrease in TKV from baseline to year 3, and the non-responder group (n = 55), defined as tolvaptan-treated patients with a net increase in TKV.

Results

Mean changes during follow-up in the placebo, responder, and non-responder groups were 16.99%, − 8.33%, and 13.95%, respectively, for TKV and − 12.61, − 8.47, and − 8.58 mL/min/1.73 m², respectively, for estimated glomerular filtration rate (eGFR). Compared with the placebo group, eGFR decline was significantly slowed in both the responder and non-responder groups (P < 0.05).

Conclusion

Tolvaptan was effective in slowing eGFR decline, regardless of TKV response, over 3 years in patients with ADPKD in Japan. Treatment with tolvaptan may have beneficial effects on slowing of renal function decline even in patients who have not experienced a reduction in the rate of TKV growth by treatment with tolvaptan.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10157-020-02009-0.

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Prostaglandins as potential targets for the treatment of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by the proliferation of fluid-filled kidney cysts that enlarge over time, causing damage to the surrounding kidney and ultimately resulting in kidney failure. Both increased cell proliferation and fluid secretion are stimulated by increased cyclic adenosine monophosphate (cAMP) in PKD kidneys, so many treatments for the disease target cAMP lowering. Prostaglandins (PG) levels are elevated in multiple animal models of PKD and mediate many of their effects by elevating cAMP levels. Inhibiting the production of PG with cyclooxygenase 2 (COX2) inhibitors reduces PG levels and reduces disease progression. However, COX inhibitors also block beneficial PG and can cause nephrotoxicity. In an orthologous model of the main form of PKD, PGD₂ and PGI₂ were the two PG highest in kidneys and most affected by a COX2 inhibitor. Future studies are needed to determine whether specific blockage of PGD₂ and/or PGI₂ activity would lead to more targeted and effective treatments with fewer undesirable side-effects.

A Comparison of Urine Dilution Ability between Adult Dominant Polycystic Kidney Disease, Other Chronic Kidney Diseases, and Healthy Control Subjects: A Case-Control Study

The final dilution of urine is regulated via aquaporin-2 water channels in the distal part of the nephron. It is unclear whether urine dilution ability in autosomal dominant polycystic kidney disease patients (ADPKD patients) differs from other patients with similar degree of impaired renal function (non-ADPKD patients). The purpose of this case control study was to measure urine dilution ability in ADPKD patients compared to non-ADPKD patients and healthy controls. Methods. Eighteen ADPKD, 16 non-ADPKD patients (both with chronic kidney disease, stage I-IV), and 18 healthy controls received an oral water load of 20 ml/kg body weight. Urine was collected in 7 consecutive periods. We measured free water clearance (C_H2O), urine osmolality, urine output, fractional excretion of sodium, urine aquaporin2 (u-AQP2), and urine epithelial sodium channel (u-ENaC). Blood samples were drawn four times (at baseline, 2 h, 4 h, and 6 hours after the water load) for analyses of plasma osmolality, vasopressin, renin, angiotensin II, and aldosterone. Brachial and central blood pressure was measured regularly during the test. Results. The three groups were age and gender matched, and the patient groups had similar renal function. One hour after water load, the ADPKD patients had an increased C_H2O compared to non-ADPKD patients (2.97 ± 2.42 ml/min in ADPKD patients vs. 1.31 ± 1.50 ml/min in non-ADPKD patients, p0.029). The reduction in u-AQP2 and u-ENaC occurred earlier in ADPKD than in non-ADPKD patients. Plasma concentrations of vasopressin, renin, angiotensin II, and aldosterone and blood pressure measurements did not show any differences that could explain the deviation in urine dilution capacity between the patient groups. Conclusions. ADPKD patients had a higher C_H2O than non-ADPKD patients after an oral water load, and u-AQP2 and u-ENaC were more rapidly reduced than in non-ADPKD patients. Thus, urine-diluting capacity may be better preserved in ADPKD patients than in non-ADPKD patients.

Primary Cilia, Ciliogenesis and the Actin Cytoskeleton: A Little Less Resorption, A Little More Actin Please

Primary cilia are microtubule-based organelles that extend from the apical surface of most mammalian cells, forming when the basal body (derived from the mother centriole) docks at the apical cell membrane. They act as universal cellular "antennae" in vertebrates that receive and integrate mechanical and chemical signals from the extracellular environment, serving diverse roles in chemo-, mechano- and photo-sensation that control developmental signaling, cell polarity and cell proliferation. Mutations in ciliary genes cause a major group of inherited developmental disorders called ciliopathies. There are very few preventative treatments or new therapeutic interventions that modify disease progression or the long-term outlook of patients with these conditions. Recent work has identified at least four distinct but interrelated cellular processes that regulate cilia formation and maintenance, comprising the cell cycle, cellular proteostasis, signaling pathways and structural influences of the actin cytoskeleton. The actin cytoskeleton is composed of microfilaments that are formed from filamentous (F) polymers of globular G-actin subunits. Actin filaments are organized into bundles and networks, and are attached to the cell membrane, by diverse cross-linking proteins. During cell migration, actin filament bundles form either radially at the leading edge or as axial stress fibers. Early studies demonstrated that loss-of-function mutations in ciliopathy genes increased stress fiber formation and impaired ciliogenesis whereas pharmacological inhibition of actin polymerization promoted ciliogenesis. These studies suggest that polymerization of the actin cytoskeleton, F-actin branching and the formation of stress fibers all inhibit primary cilium formation, whereas depolymerization or depletion of actin enhance ciliogenesis. Here, we review the mechanistic basis for these effects on ciliogenesis, which comprise several cellular processes acting in concert at different timescales. Actin polymerization is both a physical barrier to both cilia-targeted vesicle transport and to the membrane remodeling required for ciliogenesis. In contrast, actin may cause cilia loss by localizing disassembly factors at the ciliary base, and F-actin branching may itself activate the YAP/TAZ pathway to promote cilia disassembly. The fundamental role of actin polymerization in the control of ciliogenesis may present potential new targets for disease-modifying therapeutic approaches in treating ciliopathies.

Autosomal dominant polycystic kidney disease and pioglitazone for its therapy: a comprehensive review with an emphasis on the molecular pathogenesis and pharmacological aspects

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited chronic kidney disorder (CKD) that is characterized by the development of numerous fluid-filled cysts in kidneys. It is caused either due to the mutations in the PKD1 or PKD2 gene that encodes polycystin-1 and polycystin-2, respectively. This condition progresses into end-stage renal disorder if the renal or extra-renal clinical manifestations remain untreated. Several clinical trials with a variety of drugs have failed, and the only Food and Drugs Administration (FDA) approved drug to treat ADPKD to date is tolvaptan that works by antagonizing the vasopressin-2 receptor (V2R). The pathology of ADPKD is complex and involves the malfunction of different signaling pathways like cAMP, Hedgehog, and MAPK/ERK pathway owing to the mutated product that is polycystin-1 or 2. A measured yet substantial number of preclinical studies have found pioglitazone to decrease the cystic burden and improve the renal function in ADPKD. The peroxisome proliferator-activated receptor-gamma is found on the epithelial cells of renal collecting tubule and when it gets agonized by pioglitazone, confers efficacy in ADPKD treatment through multiple mechanisms. There is only one clinical trial (ongoing) wherein it is being assessed for its benefits and risk in patients with ADPKD, and is expected to get approval from the regulatory body owing to its promising therapeutic effects. This article would encompass the updated information on the epidemiology, pathophysiology of ADPKD, different mechanisms of action of pioglitazone in the treatment of ADPKD with preclinical and clinical shreds of evidence, and related safety updates.

Serum Copeptin, NLPR3, and suPAR Levels among Patients with Autosomal-Dominant Polycystic Kidney Disease with and without Impaired Renal Function

BACKGROUND

The pathophysiology of renal disease progression in autosomal-dominant polycystic kidney disease (ADPKD) involves not only cystogenesis but also endothelial dysfunction, leading to the activation of inflammatory and fibrotic pathways. This study evaluated the levels of biomarkers related to osmoregulation, immune system activation, and tubular injury in ADPKD patients with impaired or preserved renal function.

METHODS

This study included 26 ADPKD patients with modestly impaired renal function (estimated glomerular filtration rate [eGFR] 45-70 mL/min/1.73 m2; Group A), 26 age- and sex-matched ADPKD patients with relatively preserved renal function (eGFR >70 mL/min/1.73 m2; Group B), and 26 age- and sex-matched controls (Group C). Serum levels of copeptin, the inflammasome nucleotide-binding and oligomerization domain-like receptors pyrin domain-containing protein 3 (NLRP3), and soluble urokinase-type plasminogen activator receptor (suPAR) were measured with ELISA techniques.

RESULTS

Patients in Group A had higher levels of copeptin (median [interquartile range]: 50.44 [334.85] pg/mL), NLRP3 (5.86 [3.89] ng/mL), and suPAR (390.05 [476.53] pg/mL) compared to patients in Group B (32.38 [58.33], p = 0.042; 2.42 [1.96], p < 0.001; and 313.78 [178.85], p = 0.035, respectively) and Group C (6.75 [6.43]; 1.09 [0.56]; and 198.30 [28.53], respectively; p < 0.001 for all comparisons). Levels of all studied markers were also significantly higher in Group B patients compared to controls (p < 0.001), despite having similar eGFR. In patients with ADPKD, all studied biomarkers were correlated positively with asymmetric-dimethylarginine (ADMA) and endocan levels, and negatively with eGFR. ADMA and endocan levels were the only parameters independently associated with increased copeptin levels.

CONCLUSIONS

This study showed that ADPKD patients with impaired and preserved renal function had higher copeptin, NLRP3, and suPAR levels than controls. Such findings support that cystogenesis and inflammation are associated with endothelial dysfunction, even in the early stages of ADKPD.