A Practical Guide for Treatment of Rapidly Progressive ADPKD with Tolvaptan

P2Y2R and Cyst Growth in Polycystic Kidney Disease

Key Points

Background

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by multiple bilateral kidney cysts that gradually enlarge, resulting in a decline in kidney function. Cyst growth is significantly driven by ATP-dependent chloride secretion mediated by the ion channel TMEM16A. This pathway is further augmented in advanced stages of the disease by hypoxia and activation of hypoxia-inducible factor (HIF)-1α. The mechanisms by which ATP leads to activation of TMEM16A and how HIF-1α contributes to cyst growth in vivo have remained elusive.

Methods

Mice with an inducible tubule-specific deletion of Pkd1 were compared with mice with an additional codeletion of the purinergic receptor P2y2r. Furthermore, animals were challenged by pharmacological activation of HIF-1α and Pkd1-deficient mice were treated with suramin, an antagonist of purinergic signaling. In addition, expression of P2Y2R, TMEM16A, and HIF-1α was analyzed in nephrectomy samples from 27 patients with ADPKD.

Results

Genetic deletion of P2y2r significantly inhibited cyst growth in vivo. In addition, aggravation of the polycystic phenotype mediated by pharmacological activation of HIF-1α was reduced by deletion of P2y2r. Application of suramin to pharmacologically inhibit purinergic signaling also suppressed cyst enlargement in vivo. Analysis of kidney samples from 27 patients with ADPKD revealed significant expression of P2Y2R at the luminal site of the cyst-lining epithelium.

Conclusions

P2Y2R was significantly expressed in human and mouse polycystic kidneys. Deletion and antagonism of P2Y2R reduced cyst enlargement in an ADPKD mouse model.

Data driven approach to characterize rapid decline in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic kidney disease with high phenotypic variability. Furthering insights into patients' ADPKD progression could lead to earlier detection, management, and alter the course to end stage kidney disease (ESKD). We sought to identify patients with rapid decline (RD) in kidney function and to determine clinical factors associated with RD using a data-driven approach. A retrospective cohort study was performed among patients with incident ADPKD (1/1/2002-12/31/2018). Latent class mixed models were used to identify RD patients using differences in eGFR trajectories over time. Predictors of RD were selected based on agreements among feature selection methods, including logistic, regularized, and random forest modeling. The final model was built on the selected predictors and clinically relevant covariates. Among 1,744 patients with incident ADPKD, 125 (7%) were identified as RD. Feature selection included 42 clinical measurements for adaptation with multiple imputations; mean (SD) eGFR was 85.2 (47.3) and 72.9 (34.4) in the RD and non-RD groups, respectively. Multiple imputed datasets identified variables as important features to distinguish RD and non-RD groups with the final prediction model determined as a balance between area under the curve (AUC) and clinical relevance which included 6 predictors: age, sex, hypertension, cerebrovascular disease, hemoglobin, and proteinuria. Results showed 72%-sensitivity, 70%-specificity, 70%-accuracy, and 0.77-AUC in identifying RD. 5-year ESKD rates were 38% and 7% among RD and non-RD groups, respectively. Using real-world routine clinical data among patients with incident ADPKD, we observed that six variables highly predicted RD in kidney function.

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.

Notch3 as a novel therapeutic target for the treatment of ADPKD by regulating cell proliferation and renal cyst development

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic kidney disease. Emerging research indicates that the Notch signaling pathway plays an indispensable role in the pathogenesis of numerous kidney diseases, including ADPKD. Herein, we identified that Notch3 but not other Notch receptors was overexpressed in renal tissues from mice with ADPKD and ADPKD patients. Inhibiting Notch3 with γ-secretase inhibitors, which block a proteolytic cleavage required for Notch3 activation, or shRNA knockdown of Notch3 significantly delayed renal cyst growth in vitro and in vivo. Subsequent mechanistic study elucidated that the cleaved intracellular domain of Notch3 (N3ICD) and Hes1 could bind to the PTEN promoter, leading to transcriptional inhibition of PTEN. This further activated the downstream PI3K-AKT-mTOR pathway and promoted renal epithelial cell proliferation. Overall, Notch3 was identified as a novel contributor to renal epithelial cell proliferation and cystogenesis in ADPKD. We envision that Notch3 represents a promising target for ADPKD treatment.

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.

Novel Potential Therapeutic Targets in Autosomal Dominant Polycystic Kidney Disease from the Perspective of Cell Polarity and Fibrosis

Autosomal dominant polycystic kidney disease (ADPKD), a congenital genetic disorder, is a notable contributor to the prevalence of chronic kidney disease worldwide. Despite the absence of a complete cure, ongoing research aims for early diagnosis and treatment. Although agents such as tolvaptan and mTOR inhibitors have been utilized, their effectiveness in managing the disease during its initial phase has certain limitations. This review aimed to explore new targets for the early diagnosis and treatment of ADPKD, considering ongoing developments. We particularly focus on cell polarity, which is a key factor that influences the process and pace of cyst formation. In addition, we aimed to identify agents or treatments that can prevent or impede the progression of renal fibrosis, ultimately slowing its trajectory toward end-stage renal disease. Recent advances in slowing ADPKD progression have been examined, and potential therapeutic approaches targeting multiple pathways have been introduced. This comprehensive review discusses innovative strategies to address the challenges of ADPKD and provides valuable insights into potential avenues for its prevention and treatment.

Polycystic Kidney Disease Diet: What is Known and What is Safe

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by kidney cyst formation and progressive kidney function loss. Dietary interventions such as caloric restriction, intermittent fasting, and ketogenic diet have recently emerged as potential strategies to induce metabolic reprogramming and slow ADPKD progression. We review the available evidence supporting the efficacy and safety of these interventions in ADPKD. Dietary interventions show promise in managing ADPKD by improving metabolic health and reducing oxidative stress. However, while preclinical studies have shown favorable outcomes, limited clinical evidence supports their effectiveness. In addition, the long-term consequences of these dietary interventions, including their effect on adverse events in patients with ADPKD, remain uncertain. To optimize ADPKD management, patients are advised to follow a dietary regimen that aims to achieve or maintain an ideal body weight and includes high fluid intake, low sodium, and limited concentrated sweets. Caloric restriction seems particularly beneficial for patients with overweight or obesity because it promotes weight loss and improves metabolic parameters. Supplementation with curcumin, ginkgolide B, saponins, vitamin E, niacinamide, or triptolide has demonstrated uncertain clinical benefit in patients with ADPKD. Notably, β -hydroxybutyrate supplements have shown promise in animal models; however, their safety and efficacy in ADPKD require further evaluation through well-designed clinical trials. Therefore, the use of these supplements is not currently recommended for patients with ADPKD. In summary, dietary interventions such as caloric restriction, intermittent fasting, and ketogenic diet hold promise in ADPKD management by enhancing metabolic health. However, extensive clinical research is necessary to establish their effectiveness and long-term effects. Adhering to personalized dietary guidelines, including weight management and specific nutritional restrictions, can contribute to optimal ADPKD management. Future research should prioritize well-designed clinical trials to determine the benefits and safety of dietary interventions and supplementation in ADPKD.

Clinical Characteristics and Kidney Outcomes in Chinese Patients with Autosomal Dominant Polycystic Kidney Disease

Key Points

The Mayo clinic imaging classification allows more accurate risk stratification but is limited by the lack of data on non-White populations and on atypical imaging patterns. In this cohort of Chinese patients with autosomal dominant polycystic kidney disease, an atypical imaging pattern was observed in 17% of the cases, associated with later presentation and a milder disease course. There may be genotypic differences, especially among those with atypical imaging. Future genotyping studies will help to define the genetic basis for the phenotypic spectrum in Chinese patients.

Background

The management of autosomal dominant polycystic kidney disease (ADPKD) remains challenging with variable and uncertain genotype–phenotype correlations. The Mayo clinic imaging classification allows more accurate risk stratification but is limited by the atypical imaging patterns. We aim to assess the clinical characteristics and the morphology of the cystic kidneys in a cohort of Chinese patients with ADPKD.

Methods

Ninety-eight patients with ADPKD were recruited prospectively from August 2019 to December 2020 in Prince of Wales Hospital, Hong Kong. They were subsequently followed up every 6 months for a minimum of 2 years. We reviewed the clinical characteristics and magnetic resonance imaging patterns at baseline and the kidney outcome at the end of the follow-up. Atypical imaging patterns included unilateral, segmental, asymmetric, lopsided, and bilateral atrophy as defined by the Mayo Imaging Classification.

Results

The mean age was 51.5±14.3 years, and the mean eGFR 68.7±27.5 ml/min per 1.73 m2. The 98 patients included 36 male and 62 female. Seventy-six patients (77.6%) had a family history. Seventeen of the 98 (17.3%) patients had atypical imaging patterns. Compared with typical cases, atypical cases were older at the time of diagnosis (49.5±16.0 versus 33.0±13.0 years, P < 0.001) and at the time of starting antihypertensive medications (52.4±14.8 versus 39.7±11.0 years, P = 0.001) and were less likely to have a positive family history (58.8% versus 81.5%, P = 0.042). Patients with atypical patterns showed a lower eGFR decline compared with those with the typical pattern (−0.86±4.34 versus −3.44±4.07 ml/min per 1.73 m2 per year, P = 0.022).

Conclusions

In this cohort of Chinese patients with ADPKD, an atypical imaging pattern was observed in 17% of the cases, associated with later presentation and a milder disease course. Future genotyping studies will help to define the genetic architecture and the basis for the phenotypic spectrum in Chinese patients with ADPKD.

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.

An Electronic Health Record-Integrated Application for Standardizing Care and Monitoring Patients With Autosomal Dominant Polycystic Kidney Disease Enrolled in a Tolvaptan Clinic: Design and Implementation Study

Background

Tolvaptan is the only US Food and Drug Administration-approved drug to slow the progression of autosomal dominant polycystic kidney disease (ADPKD), but it requires strict clinical monitoring due to potential serious adverse events.

Objective

We aimed to share our experience in developing and implementing an electronic health record (EHR)-based application to monitor patients with ADPKD who were initiated on tolvaptan.

Methods

The application was developed in collaboration with clinical informatics professionals based on our clinical protocol with frequent laboratory test monitoring to detect early drug-related toxicity. The application streamlined the clinical workflow and enabled our nursing team to take appropriate actions in real time to prevent drug-related serious adverse events. We retrospectively analyzed the characteristics of the enrolled patients.

Results

As of September 2022, a total of 214 patients were enrolled in the tolvaptan program across all Mayo Clinic sites. Of these, 126 were enrolled in the Tolvaptan Monitoring Registry application and 88 in the Past Tolvaptan Patients application. The mean age at enrollment was 43.1 (SD 9.9) years. A total of 20 (9.3%) patients developed liver toxicity, but only 5 (2.3%) had to discontinue the drug. The 2 EHR-based applications allowed consolidation of all necessary patient information and real-time data management at the individual or population level. This approach facilitated efficient staff workflow, monitoring of drug-related adverse events, and timely prescription renewal.

Conclusions

Our study highlights the feasibility of integrating digital applications into the EHR workflow to facilitate efficient and safe care delivery for patients enrolled in a tolvaptan program. This workflow needs further validation but could be extended to other health care systems managing chronic diseases requiring drug monitoring.

Prospective Study on Individualized Dose Adjustment of Tolvaptan Based on Urinary Osmolality in Patients With ADPKD

Introduction

Tolvaptan has been shown to reduce renal volume and delay disease progression in autosomal-dominant polycystic kidney disease (ADPKD). However, no biomarkers are currently available to guide dose adjustment. We aimed to explore the possibility of individualized tolvaptan dose adjustments based on cut-off values for urinary osmolality (OsmU).

Methods

This prospective cohort study included patients with ADPKD, with rapid disease progression. Tolvaptan treatment was initiated at a dose of 45/15 mg and increased based on OsmU, with a limit set at 200 mOsm/kg. Primary renal events (25% decrease in estimated glomerular filtration rate [eGFR] during treatment), within-patient eGFR slope, and side effects were monitored during the 3-year follow-up.

Results

Forty patients participated in the study. OsmU remained below 200 mOsm/kg throughout the study period, and most patients required the minimum tolvaptan dose (mean dose, 64 [±10] mg), with a low discontinuation rate (5%). The mean annual decline in eGFR was -3.05 (±2.41) ml/min per 1.73 m2 during tolvaptan treatment, compared to the period preceding treatment, corresponding to a reduction in eGFR decline of more than 50%. Primary renal events occurred in 20% of patients (mean time to onset, 31 months; 95% confidence interval [CI] = 28-34).

Conclusion

Individualized tolvaptan dose adjustment based on OsmU in patients with ADPKD and rapid disease progression provided benefits in terms of reducing eGFR decline, compared with reference studies, and displayed lower dropout rates and fewer side effects. Further studies are required to confirm optimal strategies for the use of OsmU for tolvaptan dose adjustment in patients with ADPKD.

A combination of β-hydroxybutyrate and citrate ameliorates disease progression in a rat model of polycystic kidney disease

Our research has shown that interventions producing a state of ketosis are highly effective in rat, mouse, and cat models of polycystic kidney disease (PKD), preventing and partially reversing cyst growth and disease progression. The ketone β-hydroxybutyrate (BHB) appears to underlie this effect. In addition, we have demonstrated that naturally formed microcrystals within kidney tubules trigger a renoprotective response that facilitates tubular obstruction clearance in healthy animals but, alternatively, leads to cyst formation in PKD. The administration of citrate prevents microcrystal formation and slows PKD progression. Juvenile Cy/+ rats, a nonorthologous PKD model, were supplemented from 3 to 8 wk of age with water containing titrated BHB, citrate, or in combination to find minimal effective and optimal dosages, respectively. Adult rats were given a reduced BHB/citrate combination or equimolar control K/NaCl salts from 8 to 12 wk of age. In addition, adult rats were placed in metabolic cages following BHB, citrate, and BHB/citrate administration to determine the impact on mineral, creatinine, and citrate excretion. BHB or citrate alone effectively ameliorates disease progression in juvenile rats, decreasing markers of cystic disease and, in combination, producing a synergistic effect. BHB/citrate leads to partial disease regression in adult rats with established cystic disease, inhibiting cyst formation and kidney injury. BHB/citrate confers benefits via multiple mechanisms, increases creatinine and citrate excretion, and normalizes mineral excretion. BHB and citrate are widely available and generally recognized as safe compounds and, in combination, exhibit high promise for supporting kidney health in polycystic kidney disease.NEW & NOTEWORTHY Combining β-hydroxybutyrate (BHB) and citrate effectively slows and prevents cyst formation and expansion in young Cy/+ rats using less BHB and citrate than when used alone, demonstrating synergy. In adult rats, the combination causes a partial reversal of existing disease, reducing cyst number and cystic area, preserving glomerular health, and decreasing markers of kidney injury. Our results suggest a safe and feasible strategy for supporting kidney health in polycystic kidney disease (PKD) using a combination of BHB and citrate.

HYDROchlorothiazide versus placebo to PROTECT polycystic kidney disease patients and improve their quality of life: study protocol and rationale for the HYDRO-PROTECT randomized controlled trial

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) leads to progressive renal cyst formation and loss of kidney function in most patients. Vasopressin 2 receptor antagonists (V2RA) like tolvaptan are currently the only available renoprotective agents for rapidly progressive ADPKD. However, aquaretic side effects substantially limit their tolerability and therapeutic potential. In a preliminary clinical study, the addition of hydrochlorothiazide (HCT) to tolvaptan decreased 24-h urinary volume and appeared to increase renoprotective efficacy. The HYDRO-PROTECT study will investigate the long-term effect of co-treatment with HCT on tolvaptan efficacy (rate of kidney function decline) and tolerability (aquaresis and quality of life) in patients with ADPKD.

METHODS

The HYDRO-PROTECT study is an investigator-initiated, multicenter, double-blind, placebo-controlled, randomized clinical trial. The study is powered to enroll 300 rapidly progressive patients with ADPKD aged ≥ 18 years, with an eGFR of > 25 mL/min/1.73 m2, and on stable treatment with the highest tolerated dose of tolvaptan in routine clinical care. Patients will be randomly assigned (1:1) to daily oral HCT 25 mg or matching placebo treatment for 156 weeks, in addition to standard care.

OUTCOMES

The primary study outcome is the rate of kidney function decline (expressed as eGFR slope, in mL/min/1.73 m2 per year) in HCT versus placebo-treated patients, calculated by linear mixed model analysis using all available creatinine values from week 12 until the end of treatment. Secondary outcomes include changes in quality-of-life questionnaire scores (TIPS, ADPKD-UIS, EQ-5D-5L, SF-12) and changes in 24-h urine volume.

CONCLUSION

The HYDRO-PROTECT study will demonstrate whether co-treatment with HCT can improve the renoprotective efficacy and tolerability of tolvaptan in patients with ADPKD.

Novel hits for autosomal dominated polycystic kidney disease (ADPKD) targeting derived by in silico screening on ZINC-15 natural product database

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disorder that leads to growth cysts in the kidney, ultimately resulting in loss of function. Currently, no effective drug therapy can be safely used in the clinic. So, looking for effective therapeutic drugs is urgent for treating ADPKD. Our natural product library was prepared based on the ZINC-15 database. Lipinski's rule of five, drug-likeness, and toxicity screening of the designed library were evaluated. Swiss model online server was used for modeling of GANAB target. Finally, docking-based screening against ADPKD targets was done by MOE 2019 software. The top 14 favorable druglike and non-toxic hits were selected for docking studies. Our results showed that compound-10 (ZINC 6073947) as a sesquiterpene coumarin had more negative binding interaction into the active site of PPARG, OXSR1, GANAB, AVPR2, and PC2 with docking scores of -8.22, -7.52, -6.98, -6.61 and -6.05 kcal/mol, respectively, in comparison to Curcumin, as a natural product that is now in phase 4 clinical trial in ADPKD disease, with an affinity of -8.03, -6.42, -6.82, -5.84 and -5.10 kcal/mol, respectively. Furthermore, seven sesquiterpene coumarins similar to compound 10 were generated and docked. Farnesiferol B (16), compared to compound-10, showed binding affinity of -8.16, -6.4, -7.46, -6.92, and -6.11 kcal/mol against the above targets, respectively. Molecular dynamics, which was done on the compound-10 and 16 (Farnesiferol B) in complex with PPARG, GANAB, and AVPR2, showed more negative binding free-energy than Pioglitazone, Miglitol, and Tolvaptan as FDA-approved drugs for each target, respectively.Communicated by Ramaswamy H. Sarma.

Vasopressin V2 receptor, tolvaptan, and ERK1/2 phosphorylation in the renal collecting duct

Tolvaptan, a vasopressin antagonist selective for the V2-subtype vasopressin receptor (V2R), is widely used in the treatment of hyponatremia and autosomal-dominant polycystic kidney disease (ADPKD). Its effects on signaling in collecting duct cells have not been fully characterized. Here, we perform RNA-seq in a collecting duct cell line (mpkCCD). The data show that tolvaptan inhibits the expression of mRNAs that were previously shown to be increased in response to vasopressin including aquaporin-2, but also reveals mRNA changes that were not readily predictable and suggest off-target actions of tolvaptan. One such action is activation of the MAPK kinase (ERK1/ERK2) pathway. Prior studies have shown that ERK1/ERK2 activation is essential in the regulation of a variety of cellular and physiological processes and can be associated with cell proliferation. In immunoblotting experiments, we demonstrated that ERK1/ERK2 phosphorylation in mpkCCD cells was significantly reduced by vasopressin, in contrast to the increases seen in non-collecting-duct cells overexpressing V2R in prior studies. We also found that tolvaptan has a strong effect to increase ERK1/ERK2 phosphorylation in the presence of vasopressin and that tolvaptan's effect to increase ERK1/ERK2 phosphorylation is absent in mpkCCD cells in which both protein kinase A (PKA)-catalytic subunits have been deleted. Thus, it appears that the tolvaptan effect to increase ERK activation is PKA-dependent and is not due to an off-target effect of tolvaptan. We conclude that in cells expressing V2R at endogenous levels: 1) vasopressin decreases ERK1/ERK2 activation; 2) in the presence of vasopressin, tolvaptan increases ERK1/ERK2 activation; and 3) these effects are PKA-dependent.NEW & NOTEWORTHY Vasopressin is a key hormone that regulates the function of the collecting duct of the kidney. ERK1 and ERK2 are enzymes that play key roles in physiological regulation in all cells. The authors used collecting duct cell cultures to investigate the effects of vasopressin and the vasopressin receptor antagonist tolvaptan on ERK1 and ERK2 phosphorylation and activation.

Real-life use of tolvaptan in ADPKD: a retrospective analysis of a large Canadian cohort

Tolvaptan is the first disease-modifying drug proven to slow eGFR decline in high-risk patients with ADPKD. However, barriers from the patient perspective to its use in real-life settings have not been systemically examined in a large cohort. This was a single-center, retrospective study of 523 existing or new patients with ADPKD followed at the Center for Innovative Management of PKD in Toronto, Ontario, between January 1, 2016 to December 31, 2018. All patients underwent clinical assessment including total kidney volume measurements and Mayo Clinic Imaging Class (MCIC). Those who were deemed to be at high risk were offered tolvaptan with their preference (yes or no) and reasons for their choices recorded. Overall, 315/523 (60%) patients had MCIC 1C-1E; however, only 96 (30%) of them were treated with tolvaptan at their last follow-up. Among these high-risk patients, those not treated versus treated with tolvaptan were more likely to have a higher eGFR (82 ± 26 vs. 61 ± 27 ml/min/1.73 m2), CKD stages 1-2 (79% vs. 41%), and MCIC 1C (63% vs. 31%). The most common reasons provided for not taking tolvaptan were lifestyle preference related to the aquaretic effect (51%), older age ≥ 60 (12%), and pregnancy/family planning (6%). In this real-world experience, at least 60% of patients with ADPKD considered to be at high risk for progression to ESKD by imaging were not treated with tolvaptan; most of them had early stages of CKD with well-preserved eGFR and as such, were prime targets for tolvaptan therapy to slow disease progression. Given that the most common reason for tolvaptan refusal was the concern for intolerability of the aquaretic side-effect, strategies to mitigate this may help to reduce this barrier to tolvaptan therapy.

Comparing Effects of Tolvaptan and Instruction to Increase Water Consumption in ADPKD: Post Hoc Analysis of TEMPO 3:4

Key Points

In a post hoc analysis, short-term reduction in spot urine osmolality (Uosm) was associated with decreased kidney volume growth in autosomal dominant polycystic kidney disease for both tolvaptan and instruction to increase hydration alone. For the same spot Uosm reduction, however, the kidney volume benefit was greater with tolvaptan, possibly because of greater cumulative 24-hour Uosm suppression by tolvaptan.

Background

In addition to decreasing water excretion and increasing urinary concentration, the antidiuretic hormone vasopressin plays a role in the pathophysiology of autosomal dominant polycystic kidney disease. It has been hypothesized that by suppressing vasopressin release, drinking large amounts of water might exert therapeutic effects in autosomal dominant polycystic kidney disease similar to those of tolvaptan, an antagonist of the vasopressin type 2 receptor, but evidence is lacking. We analyzed data from tolvaptan clinical trials to evaluate relationships among water intake, urine osmolality (Uosm), and change in total kidney volume (TKV).

Methods

Analysis of the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes 3:4 clinical trial in which participants were randomized to tolvaptan or placebo and instructed to drink large amounts of water. The relationship between change in spot Uosm from baseline to week 3 and change in TKV to month 12 was assessed using linear regression modeling. Two short-term tolvaptan trials were analyzed to explore relationships between intermittent Uosm sampling and 24-hour Uosm suppression.

Results

With both tolvaptan and placebo (i.e. , mandated high water intake alone), Uosm reduction at week 3 was associated with reduction in TKV growth at month 12. However, for the same decrease in spot Uosm, the corresponding reduction in TKV growth was greater for tolvaptan (e.g. , a −250 mOsm/kg reduction in Uosm at week 3 was associated with a −1% change in TKV at month 12 for tolvaptan versus +4.5% for placebo). In short-term trials, similar reductions in spot or trough Uosm values were achievable with tolvaptan and high water intake, but cumulative 24-hour suppression was greater with tolvaptan.

Conclusions

This analysis supports a relationship between effects on Uosm and inhibition of disease progression by tolvaptan and high water intake alone. The findings further suggest that 24-hour Uosm measurement is superior to spot Uosm for assessing suppression of vasopressin activity by tolvaptan.

Beyond Loss of Kidney Function: Patient Care in Autosomal Dominant Polycystic Kidney Disease

Patients with autosomal dominant polycystic kidney disease benefit from specialized care over their lifetimes, starting with diagnosis of the condition with ongoing discussion of both the renal course and extra-renal issues. Both renal and extra-renal issues may continue to cause major morbidity even after successful kidney transplant or initiation of RRT, and extra-renal disease aspects should always be considered as part of routine management. In this review, we will focus on updates in pain/depression screening, cardiac manifestations, liver and pancreatic cysts, kidney stone management, and genetic counseling. In some instances, we have shared our current clinical practice rather than an evidence-based guideline. We anticipate more standardization of care after the release of the Kidney Disease Improving Global Outcomes guidelines for management in autosomal dominant polycystic kidney disease later this year.

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.

Non-contrast low-dose CT can be used for volumetry of ADPKD

BACKGROUND

Kidney volume provides important information for the diagnosis and prognosis of autosomal dominant polycystic kidney disease (ADPKD), as well as for the evaluation of the effects of drugs such as tolvaptan. Non-contrast computed tomography (CT) is commonly used for volumetry, and this study examined the correspondence and correlation of kidney volume measured by standard-dose or low-dose CT.

METHODS

Axial standard-dose and low-dose CT images with 1-mm slices were obtained from 24 ADPKD patients. The kidney was segmented in the Synapse 3D software and the kidney volume was calculated using stereology. The kidney volume was compared between the two sets of images using R2, Bland-Altman plots, coefficient of variation, and intra-class correlation coefficients (ICCs).

RESULTS

The mean age of the 24 patients was 48.4 ± 10.9 years, and 45.8% were men (n = 11). The mean total kidney volume on standard-dose CT was 1501 ± 838.2 mL. The R2 of volume between standard-dose and low-dose CT was 0.995. In the Bland-Altman plot, except for one case with a large kidney volume, the two measurements were consistent, and the coefficient of variation and ICC were also good (0.02, 0.998). The CT radiation dose (dose-length product) was 229 ± 68 mGy·cm for standard-dose CT and 50 ± 19 mGy·cm for low-dose CT. A comparable volume was obtained with 20% of the radiation dose of standard-dose CT.

CONCLUSIONS

Standard-dose and low-dose CT showed comparable kidney volume in ADPKD. Therefore, low-dose CT can substitute for ADPKD volumetry while minimizing radiation exposure.

Public support for patients with intractable diseases in Japan: impact on clinical indicators from nationwide registries in patients with autosomal dominant polycystic kidney disease

BACKGROUND

Clinical practice guidelines recommend antihypertensive and tolvaptan therapies for patients with autosomal dominant polycystic kidney disease (ADPKD) in Japan. However, tolvaptan therapy may pose an economic burden. The Japanese Ministry of Health, Labour and Welfare supports patients with intractable diseases. This study aimed to confirm the impact of the intractable disease system in Japan on the clinical treatment of ADPKD.

METHODS

We analyzed the data of 3768 patients with ADPKD having a medical subsidy certificate from the Japanese Ministry of Health, Labour and Welfare in 2015-2016. The following quality indicators were use: the adherence rate to the 2014 clinical practice guideline for polycystic kidney disease (prescription rates of antihypertensive agents and tolvaptan in this cohort) and the number of Japanese patients with ADPKD nationwide started on renal replacement therapy in 2014 and 2020.

RESULTS

Compared with new applications from 2015 to 2016, the prescription rates of antihypertensives and tolvaptan for the indicated patients at the 2017 renewal application increased by 2.0% (odds ratio = 1.41, p = 0.008) and 47.4% (odds ratio = 10.1, p > 0.001), respectively. These quality indicators improved with antihypertensive treatment, especially in patients with chronic kidney disease stages 1-2 (odds ratio = 1.79, p = 0.013) and in those aged < 50 years (odds ratio = 1.70, p = 0.003). The number of patients with ADPKD who were started on renal replacement therapy in Japan decreased from 999 in 2014 to 884 in 2020 in the nationwide database (odds ratio = 0.83, p < 0.001).

CONCLUSIONS

The Japanese public intractable disease support system contributes to improvement of ADPKD treatment.

Autosomal Dominant Polycystic Kidney Disease: Is There a Role for Autophagy?

Autosomal-Dominant Polycystic Kidney Disease (ADPKD) is a monogenic disorder initiated by mutations in either PKD1 or PKD2 genes, responsible for encoding polycystin 1 and polycystin 2, respectively. These proteins are primarily located within the primary cilia. The disease follows an inexorable progression, leading most patients to severe renal failure around the age of 50, and extra-renal complications are frequent. A cure for ADPKD remains elusive, but some measures can be employed to manage symptoms and slow cyst growth. Tolvaptan, a vasopressin V2 receptor antagonist, is the only drug that has been proven to attenuate ADPKD progression. Recently, autophagy, a cellular recycling system that facilitates the breakdown and reuse of aged or damaged cellular components, has emerged as a potential contributor to the pathogenesis of ADPKD. However, the precise role of autophagy in ADPKD remains a subject of investigation, displaying a potentially twofold impact. On the one hand, impaired autophagy may promote cyst formation by inducing apoptosis, while on the other hand, excessive autophagy may lead to fibrosis through epithelial to mesenchymal transition. Promising results of autophagy inducers have been observed in preclinical studies. Clinical trials are warranted to thoroughly assess the long-term safety and efficacy of a combination of autophagy inducers with metabolic and/or aquaferetic drugs. This research aims to shed light on the complex involvement of autophagy in ADPKD, explore the regulation of autophagy in disease progression, and highlight the potential of combination therapies as a promising avenue for future investigations.

Dual diagnosis of autosomal dominant polycystic kidney disease and sickle cell disease in a teenage male

BACKGROUND

Sickle cell disease (SCD) and autosomal dominant polycystic kidney disease (ADPKD) are relatively common genetic conditions with considerable overlap in clinical presentation. In addition to similarities between the signs and symptoms in sickle cell nephropathy and ADPKD, more than half of SCD patients have kidney cysts. The co-occurrence of these two diseases has not been previously reported in the literature.

CASE DIAGNOSIS/TREATMENT

A 16-year-old Black male with SCD had bilateral kidney enlargement and multiple simple cysts on ultrasound. Although kidney cysts are significantly more common in individuals affected with SCD, genetic testing with a broad kidney gene panel was performed to explore the possible presence of another underlying genetic cause of his cysts, in addition to SCD. A dual diagnosis of SCD and ADPKD was made following the identification of two copies of the common pathogenic sickle cell HBB variant (c.20A > T, p.Glu7Val) and a pathogenic missense variant in PKD1 (c.8311G > A, p.Glu2771Lys).

CONCLUSIONS

SCD and ADPKD differ in pathophysiological mechanisms and treatment regimens. As such, it will be paramount for this teenager to be closely monitored for signs of diminished kidney function and to be co-managed as he transitions to adult care to ensure proper treatment and management. Early identification of individuals with both SCD and a co-occurring condition is crucial to ensuring proper clinical management. Furthermore, identifying and reporting additional patients with SCD and ADPKD dual diagnoses will help us to understand the co-occurring disease course and optimal treatments.

The Efficacy, the Treatment Response and the Aquaretic Effects of a Three-Year Tolvaptan Regimen in Polycystic Kidney Disease Patients

Tolvaptan, a selective vasopressin V2 receptor antagonist, is the first and only approved specific treatment for Autosomal-Dominant Polycystic Kidney Disease (ADPKD), and is used in current clinical practice. Real clinical data are missing. In this retrospective study, 41 ADPKD patients received tolvaptan for 3 years, from 2018 to 2021. Total kidney volume (TKV) was measured using Magnetic Resonance Imaging, at initiation and at the end of the treatment period. A complete biochemistry/hematology profile and a 24 h urine volume collection were performed monthly for the first 18 months and every 3 months thereafter. At the end of the treatment period, the median (IQR) estimated Glomerular Filtration Rate (e-GFR) was 5.3 (-1.3, 8.7) mL/min higher than the expected e-GFR decline without treatment, while the prediction for End Stage Chronic Kidney Disease (ESKD) had been prolonged by 1 (0, 2) year. Total Kidney Volume did not change significantly (2250 (1357) mL at 3 years of treatment vs. 2180 (1091) mL expected without treatment, p = 0.48). Younger patients with a relatively preserved e-GFR, lower hypertension burden, better familiar renal prognosis and more severe imaging data showed better outcomes. The aquaretic adverse effects of tolvaptan did not affect renal function and electrolyte balance in 51 patients, in a follow-up period of 18 months. Consequently, tolvaptan seems to be effective in preventing progression of ADPKD when administered in a timely manner in patients with better familiar renal history, shorter hypertension duration and worse imaging profile. Increased diuresis does not affect treatment efficacy.

Cystic Kidney Diseases in Children and Adults: Differences and Gaps in Clinical Management

Cystic kidney diseases, when broadly defined, have a wide differential diagnosis extending from recessive diseases with a prenatal or pediatric diagnosis, to the most common autosomal-dominant polycystic kidney disease primarily affecting adults, and several other genetic or acquired etiologies that can manifest with kidney cysts. The most likely diagnoses to consider when assessing a patient with cystic kidney disease differ depending on family history, age stratum, radiologic characteristics, and extrarenal features. Accurate identification of the underlying condition is crucial to estimate the prognosis and initiate the appropriate management, identification of extrarenal manifestations, and counseling on recurrence risk in future pregnancies. There are significant differences in the clinical approach to investigating and managing kidney cysts in children compared with adults. Next-generation sequencing has revolutionized the diagnosis of inherited disorders of the kidney, despite limitations in access and challenges in interpreting the data. Disease-modifying treatments are lacking in the majority of kidney cystic diseases. For adults with rapid progressive autosomal-dominant polycystic kidney disease, tolvaptan (V2-receptor antagonist) has been approved to slow the rate of decline in kidney function. In this article, we examine the differences in the differential diagnosis and clinical management of cystic kidney disease in children versus adults, and we highlight the progress in molecular diagnostics and therapeutics, as well as some of the gaps meriting further attention.

Genetic Counseling in Kidney Disease: A Perspective

As genetic testing is increasingly integrated into nephrology practice there is a growing need for partnership with genetic experts. Genetic counselors are ideally suited to fill this role. The value of genetic counseling is born out of the clinical value of genetic test results against the backdrop of the complexity of genetic testing. Genetic counselors who specialize in nephrology are trained to understand and explain the potential effects of genes on kidney disease, which can enable patients to make informed decisions about proceeding with genetic testing, navigating variants of uncertain significance, educating on extrarenal features of hereditary kidney disease, facilitating cascade testing, providing post-test education about testing results, and assisting with family planning. Genetic counselors can partner with the nephrologist and provide the knowledge needed to maximize the use of genetic testing for patients for nephrology consultation. Genetic counseling is more than an element or extension of genetic testing; it is a dynamic, shared conversation between the patient and the genetic counselor where concerns, sentiments, information, and education are exchanged, and value-based decision making is facilitated.

Recent Advances in Sodium Magnetic Resonance Imaging and Its Future Role in Kidney Disease

Sodium imbalance is a hallmark of chronic kidney disease (CKD). Excess tissue sodium in CKD is associated with hypertension, inflammation, and cardiorenal disease. Sodium magnetic resonance imaging (23Na MRI) has been increasingly utilized in CKD clinical trials especially in the past few years. These studies have demonstrated the association of excess sodium tissue accumulation with declining renal function across whole CKD spectrum (early- to end-stage), biomarkers of systemic inflammation, and cardiovascular dysfunction. In this article, we review recent advances of 23Na MRI in CKD and discuss its future role with a focus on the skin, the heart, and the kidney itself.

Effects of tolvaptan discontinuation in patients with autosomal dominant polycystic kidney disease: a post hoc pooled analysis

BACKGROUND

Tolvaptan slows kidney function decline in patients with autosomal dominant polycystic kidney disease (ADPKD) who are at risk of rapid progression. Given that treatment requires commitment to long-term use, we evaluated the effects of tolvaptan discontinuation on the trajectory of ADPKD progression.

METHODS

This was a post hoc analysis of pooled data from two clinical trials of tolvaptan (TEMPO 2:4 [NCT00413777] and TEMPO 3:4 [NCT00428948]), an extension trial (TEMPO 4:4 [NCT01214421]), and an observational study (OVERTURE [NCT01430494]) that enrolled patients from the other trials. Individual subject data were linked longitudinally across trials to construct analysis cohorts of subjects with a tolvaptan treatment duration > 180 days followed by an off-treatment observation period of > 180 days. For inclusion in Cohort 1, subjects were required have ≥ 2 outcome assessments during the tolvaptan treatment period and ≥ 2 assessments during the follow-up period. For Cohort 2, subjects were required to have ≥ 1 assessment during the tolvaptan treatment period and ≥ 1 assessment during the follow-up period. Outcomes were rates of change in estimated glomerular filtration rate (eGFR) and total kidney volume (TKV). Piecewise-mixed models compared changes in eGFR or TKV in the on-treatment and post-treatment periods.

RESULTS

In the Cohort 1 eGFR population (n = 20), the annual rate of eGFR change (in mL/min/1.73 m2) was -3.18 on treatment and -4.33 post-treatment, a difference that was not significant (P = 0.16), whereas in Cohort 2 (n = 82), the difference between on treatment (-1.89) and post-treatment (-4.94) was significant (P < 0.001). In the Cohort 1 TKV population (n = 11), TKV increased annually by 5.18% on treatment and 11.69% post-treatment (P = 0.06). In Cohort 2 (n = 88), the annual TKV growth rates were 5.15% on treatment and 8.16% post-treatment (P = 0.001).

CONCLUSIONS

Although limited by small sample sizes, these analyses showed directionally consistent acceleration in measures of ADPKD progression following the discontinuation of tolvaptan.

An update on treatments for autosomal dominant polycystic kidney disease

ABSTRACT

Autosomal dominant polycystic kidney disease (ADPKD) is less common than primary hypertension or diabetes but should be considered as a possible cause of end-stage renal disease, especially in young patients without comorbidities. Because of ADPKD's nonspecific symptoms, the diagnosis, treatment, and pertinent patient education may be delayed. This article describes ADPKD and its management, including tolvaptan, a new treatment with the potential to reduce or delay morbidity. However, only a subset of patients qualifies for this expensive treatment.

Calcium signaling in polycystic kidney disease- cell death and survival

Polycystic kidney disease is typified by cysts in the kidney and extra-renal manifestations including hypertension and heart failure. The main genetic underpinning this disease are loss-of function mutations to the two polycystin proteins, polycystin 1 and polycystin 2. Molecularly, the disease is characterized by changes in multiple signaling pathways including down regulation of calcium signaling, which, in part, is contributed by the calcium permeant properties of polycystin 2. These signaling pathways enable the cystic cells to survive and avoid cell death. This review focuses on the studies that have emerged in the past 5 years describing how the structural insights gained from PC-1 and PC-2 inform the calcium dependent molecular pathways of autophagy and the unfolded protein response that are regulated by the polycystin proteins and how it leads to cell survival and/or cell death.

Tolvaptan and Kidney Function Decline in Older Individuals With Autosomal Dominant Polycystic Kidney Disease: A Pooled Analysis of Randomized Clinical Trials and Observational Studies

Rationale & Objective

Tolvaptan is indicated for treatment of patients with autosomal dominant polycystic kidney disease (ADPKD) at risk of rapid progression. Participants aged 56-65 years constituted a small proportion of the Replicating Evidence of Preserved Renal Function: an Investigation of Tolvaptan Safety and Efficacy in ADPKD (REPRISE) trial population. We assessed effects of tolvaptan on estimated glomerular filtration rate (eGFR) decline in participants aged >55 years.

Study Design

This was a pooled data analysis from 8 studies of tolvaptan or non-tolvaptan standard of care (SOC).

Setting & Participants

Participants aged >55 years with ADPKD were included. Data on participants in >1 study were linked longitudinally for maximum follow-up duration, with matching for age, sex, eGFR, and chronic kidney disease (CKD) stage to minimize confounding.

Interventions

Tolvaptan or non-tolvaptan SOC.

Outcomes

Treatment effects on annualized eGFR decline were compared using mixed models with fixed effects for treatment, time, treatment-by-time interaction, and baseline eGFR.

Results

In the pooled studies, 230 tolvaptan-treated and 907 SOC participants were aged >55 years at baseline. Ninety-five participant pairs from each treatment group were matched, all in CKD G3 or G4, ranging from 56.0 to 65.0 years (tolvaptan) or from 55.1 to 67.0 years (SOC). The eGFR annual decline rate was significantly reduced by 1.66 mL/min/1.73 m² (95% CI, 0.43-2.90; P = 0.009) in the tolvaptan group compared with SOC (-2.33 versus -3.99 mL/min/1.73 m²) over 3 years.

Limitations

Limitations include potential bias because of study population differences (bias risk was reduced through matching and multiple regression adjustment); vascular disease history data was not uniformly collected, and therefore not adjusted; and natural history of ADPKD precludes evaluating certain clinical endpoints within the study time frame.

Conclusions

In individuals aged 56-65 years with CKD G3 or G4, compared to a SOC group with mean GFR rate of decline ≥3 mL/min/1.73 m²/year, tolvaptan was associated with efficacy similar to that observed in the overall indication.

Funding

Otsuka Pharmaceutical Development & Commercialization, Inc (Rockville, MD).

Trial Registration

TEMPO 2:4 (NCT00413777); phase 1 tolvaptan trial (no NCT number; trial number 156-06-260); phase 2 tolvaptan trial (NCT01336972); TEMPO 4:4 (NCT01214421); REPRISE (NCT02160145); long-term tolvaptan safety extension trial (NCT02251275); OVERTURE (NCT01430494); HALT Progression of Polycystic Kidney Disease (HALT-PKD) study B (NCT01885559).

How to Estimate Kidney Growth in Patients with Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a disease characterized by a progressive kidney growth due to the development of cysts that lead to gradual destruction of the surrounding parenchyma. In the first stage, the estimated GFR will remain stable despite the reduction of the renal parenchyma because of an increase in glomerular hyperfiltration. The total kidney volume (TKV) measured with computed tomography or magnetic resonance imaging is related to the future GFR decline. Thus, TKV has become an early marker to be analyzed in all patients with ADPKD. In addition, in recent years, it has been pointed out that kidney growth rate estimated with a single TKV measurement can be a clear prognostic marker for future glomerular filtration decline. However, there is no consensus on how to measure kidney volume growth in ADPKD, so each author has used different models that, not having the same meaning, have been handled as if they produced similar values. This may lead to erroneous estimates of kidney growth rate with the consequent prognostic error. The Mayo Clinic classification is now the most widely accepted prognostic model in clinical practice to predict patients who will deteriorate faster and to decide what patients should be treated with tolvaptan. However, some aspects of this model have not been discussed in depth. Our aim in this review was to present the models that can be used to estimate kidney volume growth rate in ADPKD, to facilitate their applicability in daily clinical practice.

Kidney transcriptome and cystic kidney disease genes in zebrafish

Introduction: Polycystic kidney disease (PKD) is a condition where fluid filled cysts form on the kidney which leads to overall renal failure. Zebrafish has been recently adapted to study polycystic kidney disease, because of its powerful embryology and genetics. However, there are concerns on the conservation of this lower vertebrate in modeling polycystic kidney disease. Methods: Here, we aim to assess the molecular conservation of zebrafish by searching homologues polycystic kidney disease genes and carrying transcriptome studies in this animal. Results and Discussion: We found that out of 82 human cystic kidney disease genes, 81 have corresponding zebrafish homologs. While 75 of the genes have a single homologue, only 6 of these genes have two homologs. Comparison of the expression level of the transcripts enabled us to identify one homolog over the other homolog with >70% predominance, which would be prioritized for future experimental studies. Prompted by sexual dimorphism in human and rodent kidneys, we studied transcriptome between different sexes and noted significant differences in male vs. female zebrafish, indicating that sex dimorphism also occurs in zebrafish. Comparison between zebrafish and mouse identified 10% shared genes and 38% shared signaling pathways. String analysis revealed a cluster of genes differentially expressed in male vs. female zebrafish kidneys. In summary, this report demonstrated remarkable molecular conservation, supporting zebrafish as a useful animal model for cystic kidney disease.

Pharmacologic Management of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disorder and the fourth leading cause of end-stage kidney disease. ADPKD encompasses a wide range of morbidity in addition to chronic kidney disease and end-stage kidney disease, and its pathogenesis remains incompletely understood. Progress in the management of this condition includes the 2018 FDA approval of tolvaptan as the only mechanism-specific treatment available for individuals at risk of rapid progression. Assessing the risk of rapid progression is discussed at greater length in a separate article in this special issue. This section will address use and prescription of tolvaptan in more detail and address other therapies that may be considered in the treatment of patients with ADPKD.

Probenecid slows disease progression in a murine model of autosomal dominant polycystic kidney disease

Development of autosomal dominant polycystic kidney disease (ADPKD) involves renal epithelial cell abnormalities. Cystic fluid contains a high level of ATP that, among other effects, leads to a reduced reabsorption of electrolytes in cyst-lining cells, and thus results in cystic fluid accumulation. Earlier, we demonstrated that Pkd1RC/RC mice, a hypomorphic model of ADPKD, exhibit increased expression of pannexin-1, a membrane channel capable of ATP release. In the current study, we found that human ADPKD cystic epithelia have higher pannexin-1 abundance than normal collecting ducts. We hypothesized that inhibition of pannexin-1 function with probenecid can be used to attenuate ADPKD development. Renal function in male and female Pkd1RC/RC and control mice was monitored between 9 and 20 months of age. To test the therapeutic effects of probenecid (a uricosuric agent and a pannexin-1 blocker), osmotic minipumps were implanted in male and female Pkd1RC/RC mice, and probenecid or vehicle was administered for 42 days until 1 year of age. Probenecid treatment improved glomerular filtration rates and slowed renal cyst formation in male mice (as shown in histopathology). The mechanistic effects of probenecid on sodium reabsorption and fluid transport were tested on polarized mpkCCDcl4 cells subjected to short-circuit current measurements, and in 3D cysts grown in Matrigel. In the mpkCCDcl4 epithelial cell line, probenecid elicited higher ENaC currents and attenuated in vitro cyst formation, indicating lower sodium and less fluid retention in the cysts. Our studies open new avenues of research into targeting pannexin-1 in ADPKD pathology.

Accuracy and processing time of kidney volume measurement methods in rodents polycystic kidney disease models: superiority of semiautomated kidney segmentation

Measurement of total kidney volume (TKV) using magnetic resonance imaging (MRI) is a valuable approach for monitoring disease progression in autosomal dominant polycystic kidney disease (PKD) and is becoming more common in preclinical studies using animal models. Manual contouring of kidney MRI areas [i.e., manual method (MM)] is a conventional, but time-consuming, way to determine TKV. We developed a template-based semiautomatic image segmentation method (SAM) and validated it in three commonly used PKD models: Cys1cpk/cpk mice, Pkd1RC/RC mice, and Pkhd1pck/pck rats (n = 10 per model). We compared SAM-based TKV with that obtained by clinical alternatives including the ellipsoid formula-based method (EM) using three kidney dimensions, the longest kidney length method (LM), and MM, which is considered the gold standard. Both SAM and EM presented high accuracy in TKV assessment in Cys1cpk/cpk mice [interclass correlation coefficient (ICC) ≥ 0.94]. SAM was superior to EM and LM in Pkd1RC/RC mice (ICC = 0.87, 0.74, and <0.10 for SAM, EM, and LM, respectively) and Pkhd1pck/pck rats (ICC = 0.59, <0.10, and <0.10, respectively). Also, SAM outperformed EM in processing time in Cys1cpk/cpk mice (3.6 ± 0.6 vs. 4.4 ± 0.7 min/kidney) and Pkd1RC/RC mice (3.1 ± 0.4 vs. 7.1 ± 2.6 min/kidney, both P < 0.001) but not in Pkhd1PCK/PCK rats (3.7 ± 0.8 vs. 3.2 ± 0.5 min/kidney). LM was the fastest (∼1 min) but correlated most poorly with MM-based TKV in all studied models. Processing times by MM were longer for Cys1cpk/cpk mice, Pkd1RC/RC mice, and Pkhd1pck.pck rats (66.1 ± 7.3, 38.3 ± 7.5, and 29.2 ± 3.5 min). In summary, SAM is a fast and accurate method to determine TKV in mouse and rat PKD models.NEW & NOTEWORTHY Total kidney volume (TKV) is a valuable readout in preclinical studies for autosomal dominant and autosomal recessive polycystic kidney diseases (ADPKD and ARPKD). Since conventional TKV assessment by manual contouring of kidney areas in all images is time-consuming, we developed a template-based semiautomatic image segmentation method (SAM) and validated it in three commonly used ADPKD and ARPKD models. SAM-based TKV measurements were fast, highly reproducible, and accurate across mouse and rat ARPKD and ADPKD models.

Vaptans or voluntary increased hydration to protect the kidney: how do they compare?

The adverse effects of vasopressin (AVP) in diverse forms of chronic kidney disease have been well described. They depend on the antidiuretic action of AVP mediated by V2 receptors (V2R). Tolvaptan, a selective V2R antagonist, is now largely used for the treatment of patients with autosomal dominant polycystic kidney disease. Another way to reduce the adverse effects of AVP is to reduce endogenous AVP secretion by a voluntary increase in fluid intake. These two approaches differ in several ways, including the level of thirst and AVP. With voluntary increased drinking, plasma osmolality will decline and so will AVP secretion. Thus, not only will V2R-mediated effects be reduced, but also those mediated by V1a and V1b receptors (V1aR and V1bR). In contrast, selective V2R antagonism will induce a loss of fluid that will stimulate AVP secretion and thus increase AVP's influence on V1a and V1b receptors. V1aR is expressed in the luminal side of the collecting duct (CD) and in inner medullary interstitial cells, and their activation induces the production of prostaglandins, mostly prostaglandin E2 (PGE2). Intrarenal PGE2 has been shown to reduce sodium and water reabsorption in the CD and increase blood flow in the renal medulla, both effects contributing to increase sodium and water excretion and reduce urine-concentrating activity. Conversely, non-steroidal anti-inflammatory drugs have been shown to induce significant water and sodium retention and potentiate the antidiuretic effects of AVP. Thus, during V2R antagonism, V1aR-mediated actions may be responsible for part of the diuresis observed with this drug. These V1aR-dependent effects do not take place with a voluntary increase in fluid intake. In summary, while both strategies may have beneficial effects, the information reviewed here leads us to assume that pharmacological V2R antagonism, with resulting stimulation of V1aR and increased PGE2 production, may provide greater benefit than voluntary high water intake. The influence of tolvaptan on the PGE2 excretion rate and the possibility to use somewhat lower tolvaptan doses than presently prescribed remain to be evaluated.

Atypical Polycystic Kidney Disease as defined by Imaging

Using age- and height-adjusted total kidney volume, the Mayo Clinic Imaging Classification provides a validated approach to assess the risk of chronic kidney disease (CKD) progression in autosomal dominant polycystic kidney disease (ADPKD), but requires excluding patients with atypical imaging patterns, whose clinical characteristics have been poorly defined. We report an analysis of the prevalence, clinical and genetic characteristics of patients with atypical polycystic kidney disease by imaging. Patients from the extended Toronto Genetic Epidemiology Study of Polycystic Kidney Disease recruited between 2016 and 2018 completed a standardized clinical questionnaire, kidney function assessment, genetic testing, and kidney imaging by magnetic resonance or computed tomography. We compared the prevalence, clinical features, genetics, and renal prognosis of atypical versus typical polycystic kidney disease by imaging. Forty-six of the 523 (8.8%) patients displayed atypical polycystic kidney disease by imaging; they were older (55 vs. 43 years; P < 0.001), and less likely to have a family history of ADPKD (26.1% vs. 74.6%; P < 0.001), a detectable PKD1 or PKD2 mutation (9.2% vs. 80.4%; P < 0.001), or progression to CKD stage 3 or stage 5 (P < 0.001). Patients with atypical polycystic kidney disease by imaging represent a distinct prognostic group with a low likelihood of progression to CKD.

Combining Metformin and Drug-Loaded Kidney-Targeting Micelles for Polycystic Kidney Disease

Introduction

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease that leads to eventual renal failure. Metformin (MET), an AMP-activated protein kinase (AMPK) activator already approved for type 2 diabetes, is currently investigated for ADPKD treatment. However, despite high tolerability, MET showed varying therapeutic efficacy in preclinical ADPKD studies. Thus, newer strategies have combined MET with other ADPKD small molecule drug candidates, thereby targeting multiple ADPKD-associated signaling pathways to enhance therapeutic outcomes through potential drug synergy. Unfortunately, the off-target side effects caused by these additional drug candidates pose a major hurdle. To address this, our group has previously developed kidney-targeting peptide amphiphile micelles (KMs), which displayed significant kidney accumulation in vivo, for delivering drugs to the site of the disease.

Methods

To mitigate the adverse effects of ADPKD drugs and evaluate their therapeutic potential in combination with MET, herein, we loaded KMs with ADPKD drug candidates including salsalate, octreotide, bardoxolone methyl, rapamycin, tolvaptan, and pioglitazone, and tested their in vitro therapeutic efficacy when combined with free MET. Specifically, after determining the 40% inhibitory concentration for each drug (IC40), the size, morphology, and surface charge of drug-loaded KMs were characterized. Next, drug-loaded KMs were applied in combination with MET to treat renal proximal tubule cells derived from Pkd1flox/-:TSLargeT mice in 2D proliferation and 3D cyst model.

Results

MET combined with all drug-loaded KMs demonstrated significantly enhanced efficacy as compared to free drugs in inhibiting cell proliferation and cyst growth. Notably, synergistic effects were found for MET and KMs loaded with either salsalate or rapamycin as determined by Bliss synergy scores.

Conclusion

Together, we show drug synergy using drug-loaded nanoparticles and free MET for the first time and present a novel nanomedicine-based combinatorial therapeutic approach for ADPKD with enhanced efficacy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00753-9.

Structures of the arginine-vasopressin and oxytocin receptor signaling complexes

Arginine-vasopressin (AVP) and oxytocin (OT) are neurohypophysial hormones which share a high sequence and structure homology. These are two cyclic C-terminally amidated nonapeptides with different residues at position 3 and 8. In mammals, AVP and OT exert their multiple biological functions through a specific G protein-coupled receptor family: four receptors are identified, the V1a, V1b, V2 receptors (V1aR, V1bR and V2R) and the OT receptor (OTR). The chemical structure of AVP and OT was elucidated in the early 1950s. Thanks to X-ray crystallography and cryo-electron microscopy, it took however 70 additional years to determine the three-dimensional structures of the OTR and the V2R in complex with their natural agonist ligands and with different signaling partners, G proteins and β-arrestins. Today, the comparison of the different AVP/OT receptor structures gives structural insights into their orthosteric ligand binding pocket, their molecular mechanisms of activation, and their interfaces with canonical Gs, Gq and β-arrestin proteins. It also paves the way to future rational drug design and therapeutic compound development. Indeed, agonist, antagonist, biased agonist, or pharmacological chaperone analogues of AVP and OT are promising candidates to regulate different physiological functions and treat several pathologies.

Genetic Susceptibility to Chronic Kidney Disease: Links, Risks and Management

Chronic kidney disease (CKD) is associated with significant morbidity and mortality worldwide. In recent years, our understanding of genetic causes of CKD has expanded significantly with several renal conditions having been identified. This review discusses the current landscape of genetic kidney disease and their potential treatment options. This review will focus on cystic kidney disease, glomerular disease with genetic associations, congenital anomalies of kidneys and urinary tract (CAKUT), autosomal dominant-tubulointerstitial kidney disease (ADTKD), inherited nephrolithiasis and nephrocalcinosis.

Efficacy and safety of tolvaptan versus placebo in the treatment of patients with autosomal dominant polycystic kidney disease: a meta-analysis

OBJECTIVE

The objective of this meta-analysis was to compare the efficacy and drug safety of tolvaptan with placebo for autosomal dominant polycystic kidney disease (ADPKD).

METHODS

The PubMed, Embase, and Cochrane Library databases were searched from inception to September 10, 2021. Eligible studies comparing tolvaptan and placebo in the treatment of patients with ADPKD were included. Data were analysed using Review Manager Version 5.3.

RESULTS

Thirteen studies involving 3575 patients were included in the meta-analysis. Compared with placebo, tolvaptan had a better effect on delaying eGFR decline (MD 1.27, 95% CI 1.24-1.29, P < 0.01) and TKV increase (MD - 3.01, 95% CI - 3.55 to - 2.47, P < 0.01) in ADPKD treatment. Additionally, tolvaptan reduced the incidence of complications such as renal pain (OR 0.71, 95% CI 0.58-0.87, P < 0.01), urinary tract infection (OR 0.69, 95% CI 0.54-0.89, P < 0.01), haematuria (OR 0.68, 95% CI 0.51-0.89, P < 0.01), and hypertension (OR 0.66, 95% CI 0.52-0.82, P < 0.01). However, tolvaptan was associated with a higher incidence rate of adverse events such as thirst (OR 8.48 95% CI 4.53-15.87, P < 0.01), polyuria (OR 4.71, 95% CI 2.17-10.24, P < 0.01), and hepatic injury (OR 4.56, 95% CI 2.51-8.29, P < 0.01).

CONCLUSION

Tolvaptan can delay eGFR decline and TKV increase and reduce complications such as renal pain, urinary tract infection, haematuria, and hypertension in the treatment of ADPKD. However, tolvaptan increases the adverse effects of thirst, polyuria and hepatic injury.

Tolvaptan-induced isolated elevation of bilirubin in a patient with Gilbert syndrome

Tolvaptan is the current standard of treatment for autosomal dominant polycystic kidney disease. It operates by acting on V2 receptors and blocks vasopressin interactions, causing a reduction in the rate of renal cyst growth and preserving kidney function. The current known risks of tolvaptan involve a serious liver injury characterized by an elevation in total bilirubin and alanine transaminase and aspartate transaminase levels. In this report, we document a unique liver injury characterized by an elevated bilirubin with normal alanine transaminase and aspartate transaminase levels in a patient who is homozygous for the UGT1A1 consistent with Gilbert syndrome.

Health Disparities in Kidney Failure Among Patients With Autosomal Dominant Polycystic Kidney Disease: A Cross-Sectional Study

Rationale & Objective

Understanding potential differences in patterns of kidney failure among patients with autosomal dominant polycystic kidney disease (ADPKD) may provide insights into improving disease management. We sought to characterize patients with ADPKD and kidney failure across different race/ethnicities.

Study Design

Cross-sectional study.

Setting & Participants

Kaiser Permanente Southern California members diagnosed with ADPKD between January1, 2002, and December 31, 2018.

Exposure

ADPKD.

Outcome

Kidney failure, dialysis, or receipt of kidney transplant.

Analytical Approach

Differences in characteristics by race/ethnicity were assessed using analysis of variance F test and χ² test. To compare the range and distribution of the average age at onset of kidney failure by race/ethnicity and sex, we used box plots and confidence intervals. Multivariable logistic regression was used to estimate OR for kidney transplant.

Results

Among 3,677 ADPKD patients, 1,027 (27.3%) had kidney failure. The kidney failure cohort was comprised of Black (n=138; 30.7%), White (n=496; 30.6%), Hispanic (n=306; 24.7%), and Asian (n=87; 23.6%) patients. Hispanic patients had the youngest mean age of kidney failure onset (50 years) compared to Black (56 years) and White (57 years) patients. Black (44.2%; OR, 0.72) and Hispanic (49.7%; OR, 0.65) patients had lower rates of kidney transplantation compared to White (53.8%) patients. Preemptive kidney transplantations occurred in 15.0% of patients.

Limitations

Retrospective study design and possible misclassification of ADPKD cases. Kidney function calculations were based on equations incorporating race, potentially overestimating kidney function in African Americans. The study was conducted within a single, integrated health care system in 1 geographic region and may not be generalizable to all ADPKD patients.

Conclusions

Among a large diverse ADPKD population, we observed racial/ethnic differences in rates of kidney failure, age of kidney failure onset, and rates of kidney transplantation. Our real-world ADPKD cohort provides insight into racial/ethnic variation in clinical features of disease and potential disparities in care, which may affect ADPKD outcomes.

Considerations for genetic testing in individuals with autosomal dominant polycystic kidney disease

ABSTRACT

Autosomal dominant polycystic kidney disease (ADPKD) is a systemic, irreversible, genetic condition caused by mutations in the PKD1 and PKD2 genes, and the most common form of inherited kidney disease in the United States, affecting more than 600,000 individuals. Because the condition is autosomal dominant, there is a 50% chance that each child of an affected adult will also have the pathogenic genetic mutation. PKD1 mutation accounts for approximately 85% of ADPKD cases and is characterized by an earlier onset of disease with more rapid progression, whereas PKD2 mutation accounts for the remaining 15% of cases and is characterized by a less severe and less rapid disease course. Genetic testing is not consistently used in the management of individuals with ADPKD, although it can provide invaluable information regarding disease progression and prognosis. Genetic data are necessary to effectively communicate disease progression with patients, use current prognostic calculators, and play a role in family planning. Increasing clinician knowledge in primary care and nephrology providers will contribute to improved care for individuals affected by ADPKD.

Tolvaptan ameliorated kidney function for one elderly autosomal dominant polycystic kidney disease patient: A case report

BACKGROUND

Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth of numerous cysts within the kidneys. Disease progress of some patients often occurs at the early stage. Thus, managing and controlling disease progress is important to slow the kidney function decline especially for the patient with other disorders.

CASE SUMMARY

One 80-year-old male autosomal dominant polycystic kidney disease (ADPKD) patient with chronic kidney disease and other clinical disorders was treated with tolvaptan and edoxaban. Estimated glomerular filtration rate, creatinine and uric acid were monitored during the treatment. In addition, the whole exome sequencing was performed to screen ADPKD genetic variants. The kidney function decline was prevented after using tolvaptan and edoxaban treatment and in the meantime, a venous thromboembolism was removed and leg and pedal edema were alleviated. One mutation c.10102G>A /p.D3368N in the PKD1 gene was identified.

CONCLUSION

Tolvaptan combined with edoxaban administration could delay kidney function decline and eliminate the edema caused by the thromboembolism.