Tolvaptan: A Review in Autosomal Dominant Polycystic Kidney Disease

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.

Dehydration Accelerates Cytogenesis and Cyst Growth in Pkd1-/- Mice by Regulating Macrophage M2 Polarization

Adult autosomal dominant polycystic kidney disease (ADPKD) has been shown to be related as a "third hit" to the occurrence of acute or chronic kidney injury. Here, we examined whether dehydration, as a common kidney risk factor, could cause cystogenesis in chronic-onset Pkd1-/- mice by regulating macrophage activation. First, we confirmed that dehydration accelerated cytogenesis in Pkd1-/- mice and that macrophages infiltrated the kidney tissues even earlier than macroscopic cyst formation. Then, microarray analysis suggested that glycolysis pathway may be involved in macrophage activation in Pkd1-/- kidneys under conditions of dehydration. Further, we confirmed glycolysis pathway was activated and lactic acid (L-LA) was overproduced in the Pkd1-/- kidney under conditions of dehydration. We have already proved that L-LA strongly stimulated M2 macrophage polarization and overproduction of polyamine in macrophage in vitro, and in the present study, we further discovered that M2 polarization-induced polyamine production shortened the primary cilia length by disrupting the PC1/PC2 complex. Finally, the activation of L-LA-arginase 1-polyamine pathway contributed to cystogenesis and progressive cyst growth in Pkd1-/- mice recurrently exposed to dehydration.

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.

Effects of Hydrochlorothiazide and Metformin on Aquaresis and Nephroprotection by a Vasopressin V2 Receptor Antagonist in ADPKD: A Randomized Crossover Trial

BACKGROUND AND OBJECTIVES

The vasopressin V2 receptor antagonist tolvaptan is the only drug that has been proven to be nephroprotective in autosomal dominant polycystic kidney disease (ADPKD). Tolvaptan also causes polyuria, limiting tolerability. We hypothesized that cotreatment with hydrochlorothiazide or metformin may ameliorate this side effect.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a clinical study and an animal study. In a randomized, controlled, double-blind, crossover trial, we included 13 tolvaptan-treated patients with ADPKD. Patients were treated for three 2-week periods with hydrochlorothiazide, metformin, or placebo in random order. Primary outcome was change in 24-hour urine volume. We also measured GFR and a range of metabolic and kidney injury markers.

RESULTS

Patients (age 45±8 years, 54% women, measured GFR of 55±11 ml/min per 1.73 m²) had a baseline urine volume on tolvaptan of 6.9±1.4 L/24 h. Urine volume decreased to 5.1 L/24 h (P<0.001) with hydrochlorothiazide and to 5.4 L/24 h (P<0.001) on metformin. During hydrochlorothiazide treatment, plasma copeptin (surrogate for vasopressin) decreased, quality of life improved, and several markers of kidney damage and glucose metabolism improved. Metformin did not induce changes in these markers or in quality of life. Given these results, the effect of adding hydrochlorothiazide to tolvaptan was investigated on long-term kidney outcome in an animal experiment. Water intake in tolvaptan-hydrochlorothiazide cotreated mice was 35% lower than in mice treated with tolvaptan only. Combination treatment was superior to "no treatment" on markers of disease progression (kidney weight, P=0.003 and cystic index, P=0.04) and superior or equal to tolvaptan alone.

CONCLUSIONS

Both metformin and hydrochlorothiazide reduced tolvaptan-caused polyuria in a short-term study. Hydrochlorothiazide also reduced polyuria in a long-term animal model without negatively affecting nephroprotection.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_03_21_CJN11260821.mp3.

Natural-derived compounds and their mechanisms in potential autosomal dominant polycystic kidney disease (ADPKD) treatment

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic kidney disorder that impairs renal functions progressively leading to kidney failure. The disease affects between 1:400 and 1:1000 ratio of the people worldwide. It is caused by the mutated PKD1 and PKD2 genes which encode for the defective polycystins. Polycystins mimic the receptor protein or protein channel and mediate aberrant cell signaling that causes cystic development in the renal parenchyma. The cystic development is driven by the increased cyclic AMP stimulating fluid secretion and infinite cell growth. In recent years, natural product-derived small molecules or drugs targeting specific signaling pathways have caught attention in the drug discovery discipline. The advantages of natural products over synthetic drugs enthusiast researchers to utilize the medicinal benefits in various diseases including ADPKD.

CONCLUSION

Overall, this review discusses some of the previously studied and reported natural products and their mechanisms of action which may potentially be redirected into ADPKD.

IFT-A deficiency in juvenile mice impairs biliary development and exacerbates ADPKD liver disease

Polycystic liver disease (PLD) is characterized by the growth of numerous biliary cysts and presents in patients with autosomal dominant polycystic kidney disease (ADPKD), causing significant morbidity. Interestingly, deletion of intraflagellar transport-B (IFT-B) complex genes in adult mouse models of ADPKD attenuates the severity of PKD and PLD. Here we examine the role of deletion of an IFT-A gene, Thm1, in PLD of juvenile and adult Pkd2 conditional knockout mice. Perinatal deletion of Thm1 resulted in disorganized and expanded biliary regions, biliary fibrosis, increased serum bile acids, and a shortened primary cilium on cytokeratin 19+ (CK19+) epithelial cells. In contrast, perinatal deletion of Pkd2 caused PLD, with multiple CK19+ epithelial cell-lined cysts, fibrosis, lengthened primary cilia, and increased Notch and ERK signaling. Perinatal deletion of Thm1 in Pkd2 conditional knockout mice increased hepatomegaly, liver necrosis, as well as serum bilirubin and bile acid levels, indicating enhanced liver disease severity. In contrast to effects in the developing liver, deletion of Thm1 alone in adult mice did not cause a biliary phenotype. Combined deletion of Pkd2 and Thm1 caused variable hepatic cystogenesis at 4 months of age, but differences in hepatic cystogenesis between Pkd2- and Pkd2;Thm1 knockout mice were not observed by 6 months of age. Similar to juvenile PLD, Notch and ERK signaling were increased in adult Pkd2 conditional knockout cyst-lining epithelial cells. Taken together, Thm1 is required for biliary tract development, and proper biliary development restricts PLD severity. Unlike IFT-B genes, Thm1 does not markedly attenuate hepatic cystogenesis, suggesting differences in regulation of signaling and cystogenic processes in the liver by IFT-B and -A. Notably, increased Notch signaling in cyst-lining epithelial cells may indicate that aberrant activation of this pathway promotes hepatic cystogenesis, presenting as a novel potential therapeutic target. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Effectiveness of Tolvaptan in the Treatment for Patients with Autosomal Dominant Polycystic Kidney Disease: A Meta-analysis

AIMS AND OBJECTIVE

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a common chronic kidney disease that leads to End-Stage Renal Disease (ESRD). The key target of this therapy is to prevent the progression of kidney failure. Tolvaptan could slow kidney cyst growth and are proven highly effective. The aims of this analysis are to perform a systematic review, estimate and evaluate the efficacy and safety of tolvaptan in ADPKD patients.

MATERIALS AND METHODS

Randomized controlled trials of tolvaptan in ADPKD were identified in PubMed, Ovid, Web of Science and the Cochrane Library electronic database. The changes observed in kidney function, treatment efficiency and the incidence of adverse events between the tolvaptan and placebo groups were compared. Data were analyzed by the RevMan software.

RESULTS

Eight trials, including 7 double-blinded randomised controlled trials and 1 quasi RCT involving 1,536 patients were extracted. Significant differences in the annual rate of change in the total kidney volume TKV at any stages of CKD (MD = -3.32, 95%CI =-4.57,-2.07, I2 =70%) and the glomerular filtration rate (MD = 1.4, 95%CI = 0.83,1.97, I2 =0%) were observed between the tolvaptan group and the placebo group. Subgroup analysis of patients in different CKD stages also showed the same conclusion. There was an increase in the urine osmolality, and 24-hour urine volume in patients receiving tolvaptan. Tolvaptan reduced the rate of serious hypertension and kidney pain events in ADPKD patients. At higher doses, it increased the rate of adverse events (liver injuries, thirst, pollakiuria, and nocturia). There was no significant risk of bias in the included studies.

CONCLUSION

Tolvaptan has a beneficial effect on ADPKD, but is associated with an increase in adverse events at high doses when compared with the placebo. Further RCTs on tolvaptan may be required to support this conclusion.

Proteomics and metabolomics studies exploring the pathophysiology of renal dysfunction in autosomal dominant polycystic kidney disease and other ciliopathies

The primary cilium (PC) was considered as a vestigial organelle with no significant physiological importance, until the discovery that PC perturbation disturbs several signalling pathways and results in the dysfunction of a variety of organs. Genetic studies have demonstrated that mutations affecting PC proteins or its anchoring structure, the basal body, underlie a class of human disorders (known as ciliopathies) characterized by a constellation of clinical signs. Further investigations have demonstrated that the PC is involved in a broad range of biological processes, in both developing and mature tissues. Kidney disease is a common clinical feature of cilia disorders, supporting the hypothesis of a crucial role of the PC in kidney homoeostasis. Clinical proteomics and metabolomics are an expanding research area. Interestingly, the application of these methodologies to the analysis of urine, a biological sample that can be collected in a non-invasive fashion and possibly in large amounts, makes these studies feasible also in patients. The present article describes the most recent proteomic and metabolomic studies exploring kidney dysfunction in the setting of ciliopathies, showing the potential of these methodologies in the elucidation of disease pathophysiology and in the discovery of biomarkers.

Modern approaches to conservative therapy of polycystic kidney disease

Polycystic kidney disease (PKD) is a genetically determined pathological process associated with the formation and growth of cysts originating from the epithelial cells of the tubules and/or collecting tubes. PBP is represented by two main types - autosomal dominant (ADPKD) and autosomal recessive PKD (ARPKD), which are different diseases. The main causes of ADPKD are mutations of the PKD1 and PKD2 genes, which encode the formation of polycystin-1 and polycystin-2 proteins. ARPKD-linked mutation in the gene PKHD1, leads to total absence or defective synthesis of receptor protein primary cilia - fibrocystin. There are relationships between the structural and functional defects in the primary cilia and PBP. Mechanisms of cysts formation and growth include a) mutations of polycystines genes located on the cilia; b) increased activity of renal intracellular cAMP; c) vasopressin V2 receptors activation; d) violation of the tubular epithelium polarity (translocation of Na,K-ATPasa from basolateral to apical membrane); e) increased mTOR activity in epithelial cells lining renal cyst. The most promising directions of ADPKD therapy are blockade of vasopressin V2 receptors activation, inhibition of mTOR signaling pathways and reduction of intracellular cAMP level. The review presents clinical studies that assessed the effectiveness of named drugs in ADPKD.

Engineered Kidney Tubules for Modeling Patient-Specific Diseases and Drug Discovery

The lack of engineering systems able to faithfully reproduce complex kidney structures in vitro has made it difficult to efficiently model kidney diseases and development. Using polydimethylsiloxane (PDMS) scaffolds and a kidney-derived cell line we developed a system to rapidly engineer custom-made 3D tubules with typical renal epithelial properties. This system was successfully employed to engineer patient-specific tubules, to model polycystic kidney disease (PKD) and test drug efficacy, and to identify a potential new pharmacological treatment. By optimizing our system we constructed functional ureteric bud (UB)-like tubules from human induced pluripotent stem cells (iPSCs), and identified a combination of growth factors that induces budding morphogenesis like embryonic kidneys do. Finally, we applied this assay to investigate budding defects in UB-like tubules derived from a patient with a PAX2 mutation. Our system enables the modeling of human kidney disease and development, drug testing and discovery, and lays the groundwork for engineering anatomically correct kidney tissues in vitro and developing personalized medicine applications.

Casein kinase 1ε and 1α as novel players in polycystic kidney disease and mechanistic targets for (R)-roscovitine and (S)-CR8

Following the discovery of (R)-roscovitine's beneficial effects in three polycystic kidney disease (PKD) mouse models, cyclin-dependent kinases (CDKs) inhibitors have been investigated as potential treatments. We have used various affinity chromatography approaches to identify the molecular targets of roscovitine and its more potent analog (S)-CR8 in human and murine polycystic kidneys. These methods revealed casein kinases 1 (CK1) as additional targets of the two drugs. CK1ε expression at the mRNA and protein levels is enhanced in polycystic kidneys of 11 different PKD mouse models as well as in human polycystic kidneys. A shift in the pattern of CK1α isoforms is observed in all PKD mouse models. Furthermore, the catalytic activities of both CK1ε and CK1α are increased in mouse polycystic kidneys. Inhibition of CK1ε and CK1α may thus contribute to the long-lasting attenuating effects of roscovitine and (S)-CR8 on cyst development. CDKs and CK1s may constitute a dual therapeutic target to develop kinase inhibitory PKD drug candidates.

Canonical Wnt inhibitors ameliorate cystogenesis in a mouse ortholog of human ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) can be caused by mutations in the PKD1 or PKD2 genes. The PKD1 gene product is a Wnt cell-surface receptor. We previously showed that a lack of the PKD2 gene product, PC2, increases β-catenin signaling in mouse embryonic fibroblasts, kidney renal epithelia, and isolated renal collecting duct cells. However, it remains unclear whether β-catenin signaling plays a role in polycystic kidney disease phenotypes or if a Wnt inhibitor can halt cyst formation in ADPKD disease models. Here, using genetic and pharmacologic approaches, we demonstrated that the elevated β-catenin signaling caused by PC2 deficiency contributes significantly to disease phenotypes in a mouse ortholog of human ADPKD. Pharmacologically inhibiting β-catenin stability or the production of mature Wnt protein, or genetically reducing the expression of Ctnnb1 (which encodes β-catenin), suppressed the formation of renal cysts, improved renal function, and extended survival in ADPKD mice. Our study clearly demonstrates the importance of β-catenin signaling in disease phenotypes associated with Pkd2 mutation. It also describes the effects of two Wnt inhibitors, XAV939 and LGK974, on various Wnt signaling targets as a potential therapeutic modality for ADPKD, for which there is currently no effective therapy.

Quercetin inhibits renal cyst growth in vitro and via parenteral injection in a polycystic kidney disease mouse model

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic disease characterized by massive enlargement of fluid-filled cysts in the kidney.

High-Throughput Phenotypic Screening of Kinase Inhibitors to Identify Drug Targets for Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a prevalent disorder characterized by renal cysts that lead to kidney failure. Various signaling pathways have been targeted to stop disease progression, but most interventions still focus on alleviating PKD-associated symptoms. The mechanistic complexity of the disease, as well as the lack of functional in vitro assays for compound testing, has made drug discovery for PKD challenging. To identify modulators of PKD, Pkd1^–/– kidney tubule epithelial cells were applied to a scalable and automated 3D cyst culture model for compound screening, followed by phenotypic profiling to determine compound efficacy. We used this screening platform to screen a library of 273 kinase inhibitors to probe various signaling pathways involved in cyst growth. We show that inhibition of several targets, including aurora kinase, CDK, Chk, IGF-1R, Syk, and mTOR, but, surprisingly, not PI3K, prevented forskolin-induced cyst swelling. Additionally, we show that multiparametric phenotypic classification discriminated potentially undesirable (i.e., cytotoxic) compounds from molecules inducing the desired phenotypic change, greatly facilitating hit selection and validation. Our findings show that a pathophysiologically relevant 3D cyst culture model of PKD coupled to phenotypic profiling can be used to identify potentially therapeutic compounds and predict and validate molecular targets for PKD.

The Trafficking of the Water Channel Aquaporin-2 in Renal Principal Cells-a Potential Target for Pharmacological Intervention in Cardiovascular Diseases

Arginine-vasopressin (AVP) stimulates the redistribution of water channels, aquaporin-2 (AQP2) from intracellular vesicles into the plasma membrane of renal collecting duct principal cells. By this AVP directs 10% of the water reabsorption from the 170 L of primary urine that the human kidneys produce each day. This review discusses molecular mechanisms underlying the AVP-induced redistribution of AQP2; in particular, it provides an overview over the proteins participating in the control of its localization. Defects preventing the insertion of AQP2 into the plasma membrane cause diabetes insipidus. The disease can be acquired or inherited, and is characterized by polyuria and polydipsia. Vice versa, up-regulation of the system causing a predominant localization of AQP2 in the plasma membrane leads to excessive water retention and hyponatremia as in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), late stage heart failure or liver cirrhosis. This article briefly summarizes the currently available pharmacotherapies for the treatment of such water balance disorders, and discusses the value of newly identified mechanisms controlling AQP2 for developing novel pharmacological strategies. Innovative concepts for the therapy of water balance disorders are required as there is a medical need due to the lack of causal treatments.