Structural basis of tolvaptan binding to the vasopressin V2 receptor.

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

Early Commencement and Long-Term Continuation of Tolvaptan Treatment Attenuate Functional Impairment of Renal Vasopressin V2 Receptors and Improve Clinical Outcomes in Patients with Heart Failure.

Preserved urinary excretion of aquaporin 2, an index for the function of vasopressin V2 receptor (V2-R), has been reported to predict a favorable response of heart failure patients to treatment with tolvaptan. In this study, we investigated the long-term effects of tolvaptan treatment on clinical outcomes and V2-R function in patients with acute decompensated heart failure (ADHF). We enrolled 90 consecutive patients who were hospitalized in Sapporo Medical University Hospital for ADHF and treated with tolvaptan in the BOREAS-ADHF registry and analyzed patients who continued taking tolvaptan after discharge. The effect of tolvaptan treatment on rehospitalization for HF or death was investigated according to whether the V2-R function was preserved (first morning urine osmolarity ≥ 352 mOsm/L, High-Uosm) or impaired (Uosm < 352 mOsm/L, Low-Uosm). During a median follow-up period of 443 days, significantly fewer patients in the High-Uosm group experienced adverse events than did patients in the Low-Uosm group (P < 0.001). Among the patients with High-Uosm, early commencement of tolvaptan administration (on or before day 7 of hospitalization, Early/High-Uosm) significantly reduced adverse events compared to late administration (after day 7 of hospitalization, Late/High-Uosm). Uosm measured during the long-term follow-up period after discharge was significantly reduced compared to that before commencement of tolvaptan administration in the Late/High-Uosm group (from 468 ± 88 to 395 ± 108 mOsm, -18.3 ± 19.6%, P < 0.05) but not in the Early/High-Uosm group (from 478 ± 115 to 455 ± 133 mOsm, -0.50 ± 35.3%, P = 0.66). These findings indicate that early commencement and long-term continuation of tolvaptan treatment attenuate functional impairment of V2-R and improve clinical outcomes in ADHF patients with preserved V2-R function.

Pre-clinical evaluation of dual targeting of the GPCRs CaSR and V2R as therapeutic strategy for autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD), caused by mutations of PKD1 or PKD2 genes, is characterized by development and growth of cysts causing progressive kidney enlargement. Reduced resting cytosolic calcium and increased cAMP levels associated with the tonic action of vasopressin are two central biochemical defects in ADPKD. Here we show that co-targeting two GPCRs, the vasopressin V2 receptor (V2R) and the calcium sensing receptor, using the novel V2R antagonist lixivaptan in combination with the calcimimetic R-568, reduced cyst progression in two animal models of human PKD. Lixivaptan is expected to have a safer liver profile compared to tolvaptan, the only drug approved to delay PKD progression, based on computational model results and initial clinical evidence. PCK rat and Pkd1RC/RC mouse littermates were fed without or with lixivaptan (0.5%) and R-568 (0.025% for rats and 0.04% for mice), alone or in combination, for 7 (rats) or 13 (mice) weeks. In PCK rats, the combined treatment strongly decreased kidney weight, cyst and fibrosis volumes by 20%, 49%, and 73%, respectively, compared to untreated animals. In Pkd1RC/RC mice, the same parameters were reduced by 20%, 56%, and 69%, respectively. In both cases the combined treatment appeared nominally more effective than the individual drugs used alone. These data point to an intriguing new application for two existing drugs in PKD treatment. The potential for synergy between these two compounds suggested in these animal studies, if confirmed in appropriate clinical investigations, would represent a welcome advancement in the treatment of ADPKD.

An update on the use of tolvaptan for autosomal dominant polycystic kidney disease: consensus statement on behalf of the ERA Working Group on Inherited Kidney Disorders, the European Rare Kidney Disease Reference Network and Polycystic Kidney Disease International.

Approval of the vasopressin V2 receptor antagonist tolvaptan-based on the landmark TEMPO 3:4 trial-marked a transformation in the management of autosomal dominant polycystic kidney disease (ADPKD). This development has advanced patient care in ADPKD from general measures to prevent progression of chronic kidney disease to targeting disease-specific mechanisms. However, considering the long-term nature of this treatment, as well as potential side effects, evidence-based approaches to initiate treatment only in patients with rapidly progressing disease are crucial. In 2016, the position statement issued by the European Renal Association (ERA) was the first society-based recommendation on the use of tolvaptan and has served as a widely used decision-making tool for nephrologists. Since then, considerable practical experience regarding the use of tolvaptan in ADPKD has accumulated. More importantly, additional data from REPRISE, a second randomized clinical trial (RCT) examining the use of tolvaptan in later-stage disease, have added important evidence to the field, as have post hoc studies of these RCTs. To incorporate this new knowledge, we provide an updated algorithm to guide patient selection for treatment with tolvaptan and add practical advice for its use.

Assessing Risk of Rapid Progression in Autosomal Dominant Polycystic Kidney Disease and Special Considerations for Disease-Modifying Therapy.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of kidney failure, accounting for 5%-10% of cases. Predicting which patients with ADPKD will progress rapidly to kidney failure is critical to assess the risk-benefit ratio of any intervention and to consider early initiation of long-term kidney protective measures that will maximize the cumulative benefit of slowing disease progression. Surrogate prognostic biomarkers are required to predict future decline in kidney function. Clinical, genetic, environmental, epigenetic, and radiologic factors have been studied as predictors of progression to kidney failure in ADPKD. A complex interaction of these prognostic factors determines the number of kidney cysts and their growth rates, which affect total kidney volume (TKV). Age-adjusted TKV, represented by the Mayo imaging classification, estimates each patient's unique rate of kidney growth and provides the most individualized approach available clinically so far. Tolvaptan has been approved to slow disease progression in patients at risk of rapidly progressive disease. Several other disease-modifying treatments are being studied in clinical trials. Selection criteria for patients at risk of rapid progression vary widely among countries and are based on a combination of age, baseline glomerular filtration rate (GFR), GFR slope, baseline TKV, and TKV rate of growth. This review details the approach in assessing the risk of disease progression in ADPKD and identifying patients who would benefit from long-term therapy with disease-modifying agents.

Novel AVPR2 mutations and clinical characteristics in 28 Chinese families with congenital nephrogenic diabetes insipidus.

AIMS: To investigate genotype and phenotype of congenital nephrogenic diabetes insipidus caused by AVPR2 mutations, which is rare and limitedly studied in Chinese population. METHODS: 88 subjects from 28 families with NDI in a department (Beijing, PUMCH) were screened for AVPR2 mutations. Medical records were retrospectively reviewed and characterized. Genotype and phenotype analysis was performed. RESULTS: 23 AVPR2 mutations were identified, including six novel mutations (p.Y117D, p.W208R, p.L313R, p.S127del, p.V162Sfs*30 and p.G251Pfs*96). The onset-age ranged from 1 week to 3 years. Common presentations were polydipsia and polyuria (100%) and intermittent fever (57%). 21% and 14% of patients had short stature and mental impairment. Urine SG and osmolality were decreased, while serum osmolality and sodium were high. Urological ultrasonography results showed hydronephrosis of the kidney (52%), dilation of the ureter (48%), and thickened bladder wall or increased residual urine (32%), led to intermittent urethral catheterization (7%), cystostomy (11%) and binary nephrostomy (4%). Urological defects were developed in older patients. Genotype and phenotype analysis revealed patients with non-missense mutations had higher levels of serum sodium than missense mutations. CONCLUSION: In the first and largest case series of NDI caused by AVPR2 mutations in Chinese population, we established genetic profile and characterized clinical data, reporting six novel mutations. Further, we found genotype was associated with phenotype. This knowledge broadens genotype and phenotype spectrum of rare congenital NDI caused by AVPR2 mutations, and provides basis for studying molecular biology of AVPR2.

A NOVEL INTRAGENIC DELETION RELATED TO THE ARGININE VASOPRESSIN V2 RECEPTOR CAUSES NEPHROGENIC DIABETES INSIPIDUS.

BACKGROUND: Nephrogenic diabetes insipidus (NDI) is a disease characterized by a defective response to the antidiuretic hormone (ADH) of the renal collecting duct leading to a decline in the ability of the pro-urine concentration. CASE PRESENTATION: A 23-year-old man presented with an over 20-year history of polyuria concomitant with hydronephrosis. The diagnosis of NDI was established by gene analysis as well as a water-deprivation and vasopressin test. All exons of arginine vasopressin V2 receptor (AVPR2) gene were amplified and sequenced. A novel hemizygous intragenic inframe deletion, cDNA 255th bp to 263th bp in exon 2 of AVPR2, was identified. These relevant translations from the 85th amino acid Asp to 88th amino acid Val were missed and replaced by amino acid Glu. After treating the patient with hydrochlorothiazide, his symptoms improved significantly. CONCLUSION: The genetic analysis revealed a novel X-linked intragenic inframe deletion, AVPR2 gene cDNA 255th bp to 263th bp, causing NDI.

Determinants of Urine Volume in ADPKD Patients Using the Vasopressin V2 Receptor Antagonist Tolvaptan.

RATIONALE & OBJECTIVE: The vasopressin V2 receptor antagonist (V2RA) tolvaptan is the first drug that has been shown to slow the rate of kidney function decline in patients with autosomal dominant polycystic kidney disease (ADPKD). However, V2RAs also cause polyuria, with urine output that averages 6L/d. We assessed determinants of urine volume in patients with ADPKD using V2RAs because such information may help develop strategies to improve V2RA tolerability. STUDY DESIGN: Clinical trial of patients with ADPKD studied at baseline, after 3 weeks of V2RA treatment (tolvaptan, 90/30mg, in the last week), and after a 3-week washout period. SETTING & PARTICIPANTS: The trial included patients with ADPKD with a wide range of kidney function (measured glomerular filtration rates [mGFRs]; range, 18-148mL/min/1.73m2). INTERVENTION: Tolvaptan treatment for 3 weeks. OUTCOMES: 24-hour urine volume. ANALYTICAL APPROACH: Multivariable regression analysis with stepwise backward elimination was performed both during and without V2RA treatment to evaluate the influence of 24-hour osmolar excretion, mGFR, and total kidney volume on associations between tolvaptan and urine volume. RESULTS: Included were 27 patients (48% men, aged 46±9.8 years with mGFRs of 61±35mL/min/1.73m2). V2RA treatment caused a median increase in urine volume of 128% (interquartile range, 75%-202%), to 5,930±1,790mL. 24-hour osmolar excretion was strongly associated with 24-hour urine volume (standardized ß = 0.73; P < 0.001). During V2RA use, no independent associations were detected between 24-hour urine volume and mGFR, total kidney volume, or V2RA concentration. LIMITATIONS: Limited sample size, no standardized diets. CONCLUSIONS: Osmolar excretion is the major determinant of urine volume in patients taking V2RAs as a consequence of the inability to concentrate urine. Restriction of osmolar intake may therefore limit V2RA-induced polyuria, giving patients more control over the aquaretic side effects and improving the tolerability of these drugs.

Effect of a Vasopressin V2 Receptor Antagonist on Polycystic Kidney Disease Development in a Rat Model.

BACKGROUND: Vasopressin V2 receptor inhibition is a clinically validated mechanism of action in the treatment of autosomal dominant polycystic kidney disease (ADPKD). In this study, the effect of lixivaptan, a potent, selective vasopressin V2 antagonist, was evaluated in PCK rats, a validated animal model of PKD. METHODS: Four-week old PCK rats were fed rodent chow with 0.5% lixivaptan (low dose) or 1% lixivaptan (high dose), or chow only (control) for 8 weeks. Urine output was measured at weeks 7 and 10 of age. Animals were killed at 12 weeks of age; kidneys and livers were collected, weighted, and analyzed for cyclic adenosine 3',5'-monophosphate (cAMP) levels and cystic burden and fibrosis; serum creatinine and sodium were measured. RESULTS: Consistent with the development of a polycystic kidney phenotype, control PCK rats showed enlarged kidneys, extensive cyst formation, and early signs of serum creatinine elevation at 12 weeks of age. Compared to controls, PCK rats treated with low-dose lixivaptan showed a 26% reduction in % kidney weight/body weight (p < 0.01); a 54% reduction in kidney cystic score (p < 0.001), a histomorphometric measure of cystic burden; a 23% reduction in kidney cAMP levels (p < 0.05), a biochemical marker of disease; and a 13% reduction in plasma creatinine (p < 0.001), indicating preserved renal function. These reductions were associated with 3-fold increases in 24-h urine output, demonstrating the potent aquaretic effect of lixivaptan. The fact that the high dose was less efficacious than the low dose is discussed. CONCLUSIONS: These results provide the first evidence of the potential utility of lixivaptan for the treatment of ADPKD.

Comparison of the effects of tolvaptan and furosemide on renal water and sodium excretion in patients with heart failure and advanced chronic kidney disease: a subanalysis of the K-STAR study.

BACKGROUND: Tolvaptan (TLV) is known to increase electrolyte-free water clearance. However, TLV actions on renal electrolytes including urine sodium (uNa) excretion and its consequences are less well understood. This subanalysis investigated the effect of add-on TLV compared to increased furosemide (FUR) on both electrolyte-free water and electrolyte clearance in patients with congestive heart failure (CHF) complicated by advanced chronic kidney disease (CKD). METHODS: The Kanagawa Aquaresis Investigators Trial of TLV on HF Patients with Renal Impairment (K-STAR) was a multicenter, open-labeled, randomized, and controlled prospective clinical study. Eighty-one Japanese patients with CHF and residual signs of congestion despite oral FUR treatment (≥ 40 mg/day) were recruited and randomly assigned to a 7-day add-on treatment with either ≤ 40 mg/day FUR or ≤ 15 mg/day TLV. Electrolyte-free water clearance, electrolyte osmolar clearance and electrolyte excretion were compared between the two groups before and after therapy. RESULTS: The change (Δ) in electrolyte-free water clearance was significantly higher in the add-on TLV group than in the add-on FUR group. However, Δelectrolyte osmolar clearance was also higher in the add-on TLV group than in the increased FUR group. This was primarily because ΔuNa excretion was significantly higher in the add-on TLV group than in the increased FUR group, since Δurine potassium excretion was significantly lower in the add-on TLV group than in the increased FUR group. CONCLUSIONS: Add-on TLV may increase both renal water and Na excretion in CHF patients with advanced CKD to a greater degree than increased FUR.

Effects of Tolvaptan on Volume Overload in Patients with Heart Failure.

The present meta-analysis aimed to evaluate effects of tolvaptan on fluid retention in patients with heart failure who were non-responsive to conventional treatment and to assess differences between effects of low (≤ 15 mg/day) and high (> 15 mg/day) tolvaptan doses.Randomized controlled trials comparing add-on tolvaptan therapy and placebo or therapy with other diuretics in patients with heart failure were identified through a database search. The primary outcomes were changes in body weight and urine volume, and the secondary outcomes were changes in serum sodium and creatinine levels.In total, 14 reports were analyzed using a random effects model. Add-on tolvaptan was associated with increased urine volume [mean difference (MD), 1.44 L; 95% confidence interval (CI), 0.96 to 1.92], decreased body weight (MD, -0.99 kg; 95% CI, -1.24 to -0.74), and increased serum sodium levels (MD, 3.66 mEq/L; 95% CI, 3.43 to 3.88) within 2 days. Serum creatinine levels on day 7 were not different between the groups (MD, -0.03 mg/dL; 95% CI, -0.09 to 0.03). The high-dose group showed greater changes in urine volume, body weight, and serum sodium levels than the low-dose group. Serum creatinine levels slightly increased in the high-dose group (MD, 0.06; 95% CI, 0.04 to 0.08) and slightly decreased in the low-dose group (MD, -0.10; 95% CI, -0.19 to -0.01).Our findings suggest that add-on tolvaptan therapy for heart failure improves fluid retention in the early therapy phase. However, this drug should be properly used to avoid the worsening of renal function, which may occur at high doses.

[New Data on the Localization of the Vasopressin V2­Receptor in Patients With Essential Hypertension 2-3 Degree And Healthy Persons].

AIM: to compare the percentage of endothelial progenitor cells and exfoliated endothelial cells in the total number of cells of lymphocytic fraction in patients with essential hypertension (EH) and practically healthy persons, and to evaluate expression of vasopressin V2 receptor on the endothelial progenitor cells. MATERIALS AND METHODS: We examined 20 patients with 2-3­degree EH and 10 practically healthy persons. Clinical examination of patients included electrocardiography, echocardiography, biochemical blood analysis / isolation of Endothelial progenitor cells were isolated from blood plasma. Immunocytochemical study was performed by the method of combined staining using primary and secondary antibodies. Microscope Olympus FV10i was used for confocal microscopy of endothelial progenitor cells and exfoliated endothelial cells. RESULTS: The percentage of endothelial progenitor cells (phenotype CD31+СD133+) in the total number of cells of the lymphocytic fraction was significantly higher in patients with EH in comparison with healthy individuals (p=0.013 and p=0.008 for 2 and 3 degrees EH, respectively). The percentage of exfoliated endothelial cells (phenotype СD31+СD133-) in the total number of cells of the lymphocytic fraction was also significantly higher in patients with EH in comparison with healthy individuals (p=0.008 and p=0.019 for 2 and 3 degrees EH, respectively). For the first time we identified the localization of vasopressin V2-receptor on the membrane of endothelial progenitor cells. CONCLUSION: In patients with 2-3 degrees EH the percentage of endothelial progenitor cells and exfoliated endothelial cells of the total number of cells of the lymphocytic fraction is significantly was found to be increased. Localization of vasopressin V2­receptor on the membrane of endothelial progenitor cells was detected.

Vasopressin receptor antagonists, heart failure, and polycystic kidney disease.

The synthesis of nonpeptide orally bioavailable vasopressin antagonists devoid of agonistic activity (vaptans) has made possible the selective blockade of vasopressin receptor subtypes for therapeutic purposes. Vaptans acting on the vasopressin V2 receptors (aquaretics) have attracted attention as a possible therapy for heart failure and polycystic kidney disease. Despite a solid rationale and encouraging preclinical testing, aquaretics have not improved clinical outcomes in randomized clinical trials for heart failure. Additional clinical trials with select population targets, more flexible dosing schedules, and possibly a different drug type or combination (balanced V1a/V2 receptor antagonism) may be warranted. Aquaretics are promising for the treatment of autosomal dominant polycystic kidney disease and have been approved in Japan for this indication. More studies are needed to better define their long-term safety and efficacy and optimize their utilization.

Response to tolvaptan and its effect on prognosis in cirrhotic patients with ascites.

AIM: The vasopressin V2 receptor antagonist tolvaptan has been used for the treatment of cirrhotic patients with ascites; however, no predictor of efficacy and prognosis has been developed. We evaluated candidate predictors of response to tolvaptan treatment. METHODS: This was a single-center retrospective study. Overall, 97 Japanese cirrhotic patients (60 men, median age 63 years), who were hospitalized for ascites treatment including oral tolvaptan coupled with conventional diuretics, were enrolled. The efficacy of tolvaptan was defined as a urination increase of ≥500 mL or a urine volume ≥2000 mL/day on the day following treatment. The prognosis of tolvaptan treatment was evaluated by the post-treatment survival time by Kaplan-Meier analysis. RESULTS: Tolvaptan therapy was effective in 67% of cirrhotic patients. Patients showed -1.5 (-17.2 to +6.2) kg change in body weight and 40% achieved ≥2.0 kg reduction in body weight after 1 week of treatment. Platelet counts, urine sodium (Na) level, and urine Na/potassium (Na/K) ratio were higher, and the blood urea nitrogen (BUN)/creatinine (Cr) ratio was lower, in cases showing a response to tolvaptan. The combination of a BUN/Cr ratio ≥17.5 and urine Na/K ratio <3.09 was predictive of being non-responsive to tolvaptan, and the response rate in these patients was only 39% (P < 0.01). The mean post-treatment survival duration was significantly longer in patients who responded to tolvaptan therapy. CONCLUSIONS: Urinary BUN and Na excretion were predictive of a response to tolvaptan, and tolvaptan treatment may improve the prognosis of cirrhotic patients.

Administration of tolvaptan with reduction of loop diuretics ameliorates congestion with improving renal dysfunction in patients with congestive heart failure and renal dysfunction.

In patients with congestive heart failure and renal dysfunction, high dose of diuretics are necessary to improve congestion, which may progress to renal dysfunction. We examined the efficacy of tolvaptan with reduction of loop diuretics to improve renal function in patients with congestive heart failure and renal dysfunction. We conducted a multicenter, prospective, randomized study in 44 patients with congestive heart failure and renal dysfunction (serum creatinine concentration ≥1.1 mg/dl) treated with conventional diuretics. Patients were randomly divided into two groups: tolvaptan (15 mg) with a fixed dose of diuretics or with reducing to a half-dose of diuretics for 7-14 consecutive days. We examined the change of urine volume, body weight, serum creatinine and electrolyte concentrations in each group. Both groups demonstrated significant urine volume increase (724 ± 176 ml/day in the fixed-dose group and 736 ± 114 ml/day in the half-dose group) and body weight reduction (1.6 ± 1.5 kg and 1.6 ± 1.9 kg, respectively) from baseline, with no differences between the two groups. Serum creatinine concentration was significantly increased in the fixed-dose group (from 1.60 ± 0.47 to 1.74 ± 0.66 mg/dl, p = 0.03) and decreased in the half-dose group (from 1.98 ± 0.91 to 1.91 ± 0.97 mg/dl, p = 0.10). So the mean changes in serum creatinine concentration from baseline significantly differed between the two groups (0.14 ± 0.08 mg/dl in the fixed-dose group and -0.07 ± 0.19 mg/dl in the half-dose group, p = 0.006). The administration of tolvaptan with reduction of loop diuretics was clinically effective to ameliorate congestion with improving renal function in patients with congestive heart failure and renal dysfunction.

Polycystic Kidney Disease and the Vasopressin Pathway.

Vasopressin, also known as arginine vasopressin or antidiuretic hormone, plays a pivotal role in maintaining body homeostasis. Increased vasopressin concentrations, measured by its surrogate copeptin, have been associated with disease severity as well as disease progression in polycystic kidney disease (PKD), and in experimental studies vasopressin has been shown to directly regulate cyst growth. Blocking vasopressin effects on the kidney via the vasopressin V2-receptor and lower circulating vasopressin concentration are potential treatment opportunities that have been the subject of study in PKD in recent years. Treatment with vasopressin V2-receptor antagonist tolvaptan has been shown to inhibit disease progression in experimental studies, as well as in a large randomized controlled trial involving 1,445 patients with autosomal dominant PKD, lowering total kidney volume growth from 5.5 to 2.8%, and the slope of the reciprocal of the serum creatinine level from -3.81 to -2.61 mg per mL-1/year. Alternatively, lowering circulating vasopressin could delay disease progression. Vasopressin is secreted in response to an increased plasma osmolality, which in turn is caused by a low fluid or high osmolar intake. Other lifestyle factors, like smoking, increase vasopressin concentration. Here, we provide a comprehensive review of the physiology as well as pathophysiology of vasopressin in PKD, the promising effects of tolvaptan treatment, and potential synergistic or additive treatments in combination with tolvaptan. In this study, we also review current evidence regarding the effect of influencing disease progression in PKD by lifestyle changes, especially by fluid intake.

Recommendations for the use of tolvaptan in autosomal dominant polycystic kidney disease: a position statement on behalf of the ERA-EDTA Working Groups on Inherited Kidney Disorders and European Renal Best Practice.

Recently, the European Medicines Agency approved the use of the vasopressin V2 receptor antagonist tolvaptan to slow the progression of cyst development and renal insufficiency of autosomal dominant polycystic kidney disease (ADPKD) in adult patients with chronic kidney disease stages 1-3 at initiation of treatment with evidence of rapidly progressing disease. In this paper, on behalf of the ERA-EDTA Working Groups of Inherited Kidney Disorders and European Renal Best Practice, we aim to provide guidance for making the decision as to which ADPKD patients to treat with tolvaptan. The present position statement includes a series of recommendations resulting in a hierarchical decision algorithm that encompasses a sequence of risk-factor assessments in a descending order of reliability. By examining the best-validated markers first, we aim to identify ADPKD patients who have documented rapid disease progression or are likely to have rapid disease progression. We believe that this procedure offers the best opportunity to select patients who are most likely to benefit from tolvaptan, thus improving the benefit-to-risk ratio and cost-effectiveness of this treatment. It is important to emphasize that the decision to initiate treatment requires the consideration of many factors besides eligibility, such as contraindications, potential adverse events, as well as patient motivation and lifestyle factors, and requires shared decision-making with the patient.

Extracellular pH affects phosphorylation and intracellular trafficking of AQP2 in inner medullary collecting duct cells.

Kidney collecting duct cells are continuously exposed to the changes of extracellular pH (pHe). We aimed to study the effects of altered pHe on desmopressin (dDAVP)-induced phosphorylation (Ser(256), Ser(261), Ser(264), and Ser(269)) and apical targeting of aquaporin-2 (AQP2) in rat kidney inner medullary collecting duct (IMCD) cells. When freshly prepared IMCD tubule suspensions exposed to HEPES buffer with pH 5.4, 6.4, 7.4, or 8.4 for 1 h were stimulated with dDAVP (10(-10) M, 3 min), AQP2 phosphorylation at Ser(256), Ser(264), and Ser(269) was significantly attenuated under acidic conditions. Next, IMCD cells primary cultured in transwell chambers were exposed to a transepithelial pH gradient for 1 h (apical pH 6.4, 7.4, or 8.4 vs. basolateral pH 7.4 and vice versa). Immunocytochemistry and cell surface biotinylation assay revealed that exposure to either apical pH 6.4 or basolateral pH 6.4 for 1 h was associated with decreased dDAVP (10(-9) M, 15 min, basolateral)-induced apical targeting of AQP2 and surface expression of AQP2. Fluorescence resonance energy transfer analysis revealed that the dDAVP (10(-9) M)-induced increase of PKA activity was significantly attenuated when LLC-PK1 cells were exposed to pHe 6.4 compared with pHe 7.4 and 8.4. In contrast, forskolin (10(-7) M)-induced PKA activation and dDAVP (10(-9) M)-induced increases of intracellular Ca(2+) were not affected. Taken together, dDAVP-induced phosphorylation and apical targeting of AQP2 are attenuated in IMCD cells under acidic pHe, likely via an inhibition of vasopressin V2 receptor-G protein-cAMP-PKA actions.

Short-term Effects of Tolvaptan in Individuals With Autosomal Dominant Polycystic Kidney Disease at Various Levels of Kidney Function.

BACKGROUND: A recent study showed that tolvaptan, a vasopressin V2 receptor antagonist, decreased total kidney volume (TKV) growth and estimated glomerular filtration rate (GFR) loss in autosomal dominant polycystic kidney disease (ADPKD) with creatinine clearance≥60mL/min. The aim of our study was to determine whether the renal hemodynamic effects and pharmacodynamic efficacy of tolvaptan in ADPKD are dependent on GFR. STUDY DESIGN: Clinical trial with comparisons before and after treatment. SETTING & PARTICIPANTS: Patients with ADPKD with a wide range of measured GFRs (mGFRs; 18-148 mL/min) in a hospital setting. INTERVENTION: Participants were studied at baseline and after 3 weeks of treatment with tolvaptan given in increasing dosages, if tolerated (doses of 60, 90, and 120mg/d in weeks 1, 2, and 3, respectively). OUTCOMES: Change in markers for aquaresis (free-water clearance, urine and plasma osmolality, 24-hour urine volume, and plasma copeptin) and kidney injury (TKV and kidney injury biomarkers). MEASUREMENTS: GFR was measured by (125)I-iothalamate clearance; TKV, by magnetic resonance imaging; biomarker excretion, by enzyme-linked immunosorbent assay; and osmolality, by freezing point depression. RESULTS: In 27 participants (52% men; aged 46±10 years; mGFR, 69±39mL/min; TKV, 2.15 [IQR, 1.10-2.77] L), treatment with tolvaptan led to an increase in urine volume and free-water clearance and a decrease in urine osmolality, TKV, and kidney injury marker excretion. Changes in urine volume and osmolality with treatment were less in participants with lower baseline mGFRs (both P<0.01). However, change in fractional free-water clearance was greater at lower baseline mGFRs (P=0.001), suggesting that participants with decreased GFRs responded more to tolvaptan per functioning nephron. LIMITATIONS: Limited sample size, no control group. CONCLUSIONS: In patients with ADPKD with decreased kidney function, response to tolvaptan is lower for TKV, urinary volume, and osmolality, but larger for fractional free-water clearance. This latter finding suggests that patients with ADPKD with lower GFRs might benefit from long-term treatment with tolvaptan, as has been observed for patients with preserved GFRs.

The short-term and long-term effects of tolvaptan in patients with heart failure: a meta-analysis of randomized controlled trials.

A comprehensive evaluation of the benefits of tolvaptan for the management of heart failure (HF) is lacking. The objective of this meta-analysis was to assess the short-term and long-term effects of tolvaptan in patients with HF. Articles were searched from PubMed, MEDLINE and Cochrane Library before March 31, 2015. Randomized controlled trials enrolling adult HF patients and reporting the all-cause mortality, cardiac events, body weight change or changes of serum electrolytes including sodium, potassium and creatinine were included in our meta-analysis. Ten studies covering 5574 patients met the inclusion criteria. Based on the data of meta-analysis, tolvaptan had no impact on the all-cause mortality [relative risk (RR) 0.96; 95 % confidence interval (CI) 0.87-1.06; P = 0.40] and incidence of cardiac events (RR 1.03; 95 % CI 0.96-1.11; P = 0.40) of HF patients. Furthermore, in comparison with control treatments, tolvaptan significantly decreased the body weight [weight mean difference (WMD), -0.87; 95 % CI -1.03 to -0.71; P < 0.001] and statistically increased serum sodium (WMD, 2.58; 95 % CI -1.83 to 3.33; P < 0.001) without any change in serum potassium (WMD, 0.01; 95 % CI -0.03 to 0.05; P = 0.577). However, serum creatinine may be increased slightly by tolvaptan (WMD, 0.05; 95 % CI 0.03-0.07; P < 0.001). This meta-analysis suggests that in HF patients, tolvaptan may not bring long-term benefits, but it effectively improves the volume overload and hyponatremia without obvious increases in serum potassium and creatinine. Hence, tolvaptan is likely to be a promising diuretic for the treatment of HF.