Urine Aquaporin-2: A Promising Marker of Response to the Arginine Vasopressin Type-2 Antagonist, Tolvaptan in Patients with Congestive Heart Failure

Short-term impact of kampo goreisan in patients with congestive heart failure refractory to tolvaptan-incorporated medical therapy

We often encounter patients with congestive heart failure refractory to conventional diuretics therapy. Kampo goreisan (Tsumura &Co. Tokyo, Japan) is receiving great concern in mediating body water balance, particularly for such a cohort. However, its detailed biological mechanism remains uncertain. Patients who received goreisan to treat congestive heart failure refractory to tolvaptan-incorporated medical therapy were prospectively included and observed for one week during the therapeutic period. The change in urine biomarkers during the first 24 h was assessed as a primary concern. Baseline factors associated with an increase in urine volume during the first 24 h were investigated as a secondary concern. A total of 18 patients were included. Median age was 81 (77, 86) and 12 (67%) were men. During the first 24 h after the initiation of goreisan, urine cyclic AMP tended to decrease, urine aquaporin-2 decreased significantly, urine osmolality decreased significantly, and urine volume tended to increase. Baseline higher common logarithm of plasma B-type natriuretic peptide was associated with any increases in urine volume during the first 24 h with an odds ratio of 73.2 (95% confidence interval 1.04-5149, p = 0.048). Baseline plasma B-type natriuretic peptide level had a positive correlation with a change in urine volume between baseline and day 1 (r = 0.533, p = 0.026). Goreisan may increase urine volume even in patients with congestive heart failure refractory to tolvaptan-incorporated medical therapy by modulating aquaporin-2 systems in the collecting duct, particularly in individuals with advanced heart failure accompanying significant congestion. Goreisan may have a regulatory effect on body fluid, rather than just forcing aquaresis.

Aquaporins in Cardiovascular System

Recent studies have shown that aquaporins (AQPs) are involved in the regulation of cardiovascular function and the development of related diseases, especially in cerebral ischemia, congestive heart failure, hypertension, and angiogenesis. Therefore, further studies are needed to elucidate the mechanism accounting for the association between AQPs and vascular function-related diseases, which may lead to novel approaches to the prevention and treatment of those diseases. Here we will discuss the expression and physiological roles of AQPs in vascular tissues and summarize recent progress in the research on AQPs related cardiovascular diseases.

Initial clinical experience of intravenous tolvaptan sodium phosphate in patients with congestive heart failure

Tolvaptan sodium phosphate (Samtas®; Otsuka Pharmaceutical, Tokyo, Japan) is a newly available intravenous aquaretic diuretic (commercially available from May 2022), which acts as an arginine vasopressin V2 receptor antagonist. Thus far, optimal patient selection as well as safety and efficacy in real-world practice remain unknown. We experienced two patients with congestive heart failure treated with tolvaptan sodium phosphate. In one patient with right-sided heart failure, oral tolvaptan was converted to intravenous tolvaptan sodium phosphate, and another one with right and left-sided heart failure and impaired swallowing function received intravenous tolvaptan sodium phosphate on a de novo basis. Following the initiation of tolvaptan sodium phosphate, their congestive symptoms ameliorated immediately without any complications. Tolvaptan sodium phosphate may be safe and effective in real-world practice, although further studies are warranted to establish optimal patient selection and clinical management.

Learning objective

We report here an initial experience of newly-introduced intravenous tolvaptan sodium phosphate in real-world practice. The novel medication might be particularly suitable for those with severe thirst, congestive gut edema, or requiring rapid amelioration of systemic/pulmonary congestion, although further accumulating experiences are warranted to establish optimal therapeutic strategy.

Aquaporins: Important players in the cardiovascular pathophysiology

Aquaporin is a membrane channel protein widely expressed in body tissues, which can control the input and output of water in cells. AQPs are differentially expressed in different cardiovascular tissues and participate in water transmembrane transport, cell migration, metabolism, inflammatory response, etc. The aberrant expression of AQPs highly correlates with the onset of ischemic heart disease, myocardial ischemia-reperfusion injury, heart failure, etc. Despite much attention to the regulatory role of AQPs in the cardiovascular system, the translation of AQPs into clinical application still faces many challenges, including clarification of the localization of AQPs in the cardiovascular system and mechanisms mediating cardiovascular pathophysiology, as well as the development of cardiovascular-specific AQPs modulators.Therefore, in this study, we comprehensively reviewed the critical roles of AQP family proteins in maintaining cardiovascular homeostasis and described the underlying mechanisms by which AQPs mediated the outcomes of cardiovascular diseases. Meanwhile, AQPs serve as important therapeutic targets, which provide a wide range of opportunities to investigate the mechanisms of cardiovascular diseases and the treatment of those diseases.

Predictive Value of Urinary Aquaporin 2 for Acute Kidney Injury in Patients with Acute Decompensated Heart Failure

Acute kidney injury (AKI) is frequently encountered in people with acute decompensated heart failure (ADHF) and is associated with increased morbidity and mortality. Early detection of a urinary biomarker of kidney injury might allow a prompt diagnosis and improve outcomes. Levels of urinary aquaporin 2 (UAQP2), which is also associated with several renal diseases, are increased with ADHF. We aimed to determine whether UAQP2 predicted AKI in patients with ADHF. We conducted a prospective observation study in the coronary care unit (CCU) in a tertiary care university hospital in Taiwan. Individuals with ADHF admitted to the CCU between November 2009 and November 2014 were enrolled, and serum and urinary samples were collected. AKI was diagnosed in 69 (36.5%) of 189 adult patients (mean age: 68 years). Area under the receiver operating characteristic curve (AUROC) of biomarkers was evaluated to evaluate the diagnostic power for AKI. Both brain natriuretic peptide and UAQP2 demonstrated acceptable AUROCs (0.759 and 0.795, respectively). A combination of the markers had an AUROC of 0.802. UAQP2 is a potential biomarker of AKI in CCU patients with ADHF. Additional research on this novel biomarker is required.

Peak Lag Between Plasma Vasopressin and Urine Aquaporin-2 Following Cardiac Surgery

Tolvaptan, a vasopressin type-2 receptor antagonist, is utilized to ameliorate fluid retention following cardiac surgery. However, the optimal timing of tolvaptan administration considering novel biomarkers remains unknown. We prospectively included patients who underwent cardiac surgery between 2016 and 2020. We measured perioperative trends of free water reabsorption mediators including plasma arginine vasopressin and urine aquaporin-2. A total of 20 patients (68 [60, 75] years old, 18 men) were included. Urine volume decreased gradually after the initial 3 hours following cardiac surgery. The plasma arginine vasopressin level increased significantly with a peak at postoperative 6 hours, whereas the urine aquaporin-2 level increased later with a delayed peak at postoperative 12 hours. As a result, urine aquaporin-2 relative to the plasma arginine vasopressin level, which represents the activity of the collecting ducts and indicates predicted responses to tolvaptan, was a minimum at postoperative 6 hours. Tolvaptan administration immediately after cardiac surgery might not be recommended given the transient refractoriness to tolvaptan probably due to the stunning of kidney collecting ducts.

Aquaporins and diseases pathogenesis: From trivial to undeniable involvements, a disease-based point of view

Aquaporins (AQPs), as transmembrane proteins, were primarily identified as water channels with the ability of regulating the transmission of water, glycerol, urea, and other small-sized molecules. The classic view of AQPs involvement in therapeutic plan restricted them and their regulators into managing only a narrow spectrum of the diseases such as diabetes insipidus and the syndrome of inappropriate ADH secretion. However, further investigations performed, especially in the third millennium, has found that their cooperation in water transmission control can be manipulated to handle other burden-imposing diseases such as cirrhosis, heart failure, Meniere's disease, cancer, bullous pemphigoid, eczema, and Sjögren's syndrome.

Expression of aquaporin-2 in the collecting duct and responses to tolvaptan

Tolvaptan, a vasopressin type-2 receptor antagonist, is indicated for fluid retention. It is considered that the response to tolvaptan reduces as renal function deteriorates, whereas we sometimes experience "non-responders" to tolvaptan despite well-preserved renal function. While the expression of aquaporin-2 might be a key to response to tolvaptan, detailed mechanism of refractoriness to tolvaptan remains unknown. We experienced two patients with congestive heart failure and diabetic nephropathy, in whom the responses to tolvaptan were uniquely opposite. In one case, immunohistochemical staining showed expression of aquaporin-2 in the collecting duct despite severely reduced renal function, followed by the good response to tolvaptan with increased urine output. In another case, immunohistochemical staining showed absence of aquaporin-2 with infiltration of inflammatory cells in the kidney medulla despite relatively preserved renal function, followed by refractoriness to tolvaptan without any increase in urine output. Inactivated aquaporin-2 expression in the collecting duct, which was for example caused by pre-clinical urinary infection as our latter case, might have an association with refractoriness to tolvaptan.

Aquaporin-2 expression in the kidney and urine is elevated in rats with monocrotaline-induced pulmonary heart disease

Objective

Little is known about how renal aquaporin-2 (AQP2) expression is affected by right heart failure caused by pulmonary heart disease (PHD). Therefore, we examined the expression of AQP2 in a rat model of PHD induced by monocrotaline (MCT).

Methods

After 4 weeks of treatment, urine and blood samples were collected from sham-treated and MCT-treated rats. Plasma arginine vasopressin (AVP) levels were measured by radioimmunoassay, and kidney Aqp2 mRNA expression was detected by reverse transcription (RT)-PCR. Kidney AQP2 protein expression was quantified by immunohistochemistry and western blotting assays. The concentration of urine AQP2 was determined by indirect enzyme-linked immunosorbent assay.

Results

We successfully established an animal model of MCT-induced PHD in rats. MCT-treated rats had significantly higher mRNA and protein levels of AQP2 in their kidney tissue. Following MCT treatment, rats also had markedly increased concentrations of both urine AQP2 and plasma AVP.

Conclusions

AQP2 expression was significantly increased in the kidney tissues and urine of rats with PHD induced by MCT. Our findings suggest that the evaluation of AQP2 expression contributes to an early diagnosis of PHD, and may also be an important reference to improve PHD therapeutics.

Aquaporins in the kidney: physiology and pathophysiology

The kidney is the central organ involved in maintaining water and sodium balance. In human kidneys, nine aquaporins (AQPs), including AQP1-8 and AQP11, have been found and are differentially expressed along the renal tubules and collecting ducts with distinct and critical roles in the regulation of body water homeostasis and urine concentration. Dysfunction and dysregulation of these AQPs result in various water balance disorders. This review summarizes current understanding of physiological and pathophysiological roles of AQPs in the kidney, with a focus on recent progress on AQP2 regulation by the nuclear receptor transcriptional factors. This review also provides an overview of AQPs as clinical biomarkers and therapeutic targets for renal diseases.

Impact of chronic kidney disease on the diuretic response of tolvaptan in acute decompensated heart failure

Aim

This study investigated the relationship between the initial diuretic response to tolvaptan and clinical predictors for tolvaptan responders in patients with acute decompensated heart failure (ADHF).

Methods and results

Patients (153) with ADHF (clinical scenario 2 or 3 with signs of fluid retention) who were administered tolvaptan were enrolled. Tolvaptan (15 or 7.5 mg) was administered for at least 7 days to those patients in whom fluid retention was observed even after standard treatment. The maximum urine volume immediately after tolvaptan administration showed good correlations with the ejection fraction and estimated glomerular filtration rate that were independent predictors of the urine volume (UV) responders (≥1500 mL increase in urine volume). The diuretic response (in terms of maximum diuresis) diminished with advancing chronic kidney disease (CKD) stage and concomitant deterioration of the renal function. Furthermore, advanced CKD was a significant negative predictor for the body weight (BW) responders (2.0% decrease in the body weight within 1 week after starting tolvaptan). As compared with non‐CKD, the presence of advanced CKD predicts poor diuretic response for both UV and BW responders.

Conclusions

The diuretic response following tolvaptan administration gradually diminished with progressive deterioration of the CKD stage. Worsening renal function was not observed. Tolvaptan is effective in treating CS2 or CS3 ADHF patients who present fluid retention and congestion, suggesting its potential efficacy for fluid management in the ADHF patients with CKD without worsening the renal function.

Use of tolvaptan vs. furosemide in older patients with heart failure : Meta-analysis of randomized controlled trials

BACKGROUND

It is not known whether older patients with acute heart failure (HF) receiving tolvaptan have decreased mortality rates and a better long-term prognosis than patients who receive furosemide. We conducted a systematic review of randomized controlled trials (RCTs) to address this issue.

METHODS

The Medline, Embase, and Cochrane Library databases were searched for English-language RCTs published before September 2016 comparing tolvaptan with furosemide treatment in older patients (>65 years old) after acute HF. The primary outcomes assessed were 6‑month all-cause mortality and worsening renal function (WRF); the secondary outcomes were electrolyte disorders, hospital readmissions, and adverse events.

RESULTS

Out of 669 citations, six RCTs met the inclusion criteria for this meta-analysis. There was a significant decrease in WRF (relative risk [RR] = 0.67, 95% confidence interval [CI] = 0.52-0.86, p = 0.002) and in the hospitalization period (mean difference [MD] = -1.86, 95% CI = -3.70--0.02, p = 0.05), as well as a significant increase in urine volume within 3 days of tolvaptan administration (MD = 1.59, 95% CI = 1.41-1.76, p < 0.00001). There were significant differences in creatinine levels between subgroups (MD = 0.33, 95% CI = 0.14-0.52, p = 0.0006). However, for the outcome of 6‑month all-cause mortality (RR = 0.56, 95% CI = 0.29-1.06, p = 0.07), there was no significant difference among all subgroups. There were significant differences in serum sodium concentration (MD = 0.68, 95% CI = 0.02-1.34, p = 0.04) but no significant changes in systolic blood pressure (MD = 3.57, 95% CI = -2.33-9.47, p = 0.24) between groups.

CONCLUSION

In older patients, tolvaptan relieves WRF, reduces the hospitalization period, and increases urine volume without significant effects on blood pressure. However, surprisingly, the use of tolvaptan did not influence 6‑month all-cause mortality.

The V2 receptor antagonist tolvaptan raises cytosolic calcium and prevents AQP2 trafficking and function: an in vitro and in vivo assessment

Tolvaptan, a selective vasopressin V2 receptor antagonist, is a new generation diuretic. Its clinical efficacy is in principle due to impaired vasopressin‐regulated water reabsorption via aquaporin‐2 (AQP2). Nevertheless, no direct in vitro evidence that tolvaptan prevents AQP2‐mediated water transport, nor that this pathway is targeted in vivo in patients with syndrome of inappropriate antidiuresis (SIAD) has been provided. The effects of tolvaptan on the vasopressin–cAMP/PKA signalling cascade were investigated in MDCK cells expressing endogenous V2R and in mouse kidney. In MDCK, tolvaptan prevented dDAVP‐induced increase in ser256‐AQP2 and osmotic water permeability. A similar effect on ser256‐AQP2 was found in V1aR −/− mice, thus confirming the V2R selectively. Of note, calcium calibration in MDCK showed that tolvaptan per se caused calcium mobilization from the endoplasmic reticulum resulting in a significant increase in basal intracellular calcium. This effect was only observed in cells expressing the V2R, indicating that it requires the tolvaptan–V2R interaction. Consistent with this finding, tolvaptan partially reduced the increase in ser256‐AQP2 and the water permeability in response to forskolin, a direct activator of adenylyl cyclase (AC), suggesting that the increase in intracellular calcium is associated with an inhibition of the calcium‐inhibitable AC type VI. Furthermore, tolvaptan treatment reduced AQP2 excretion in two SIAD patients and normalized plasma sodium concentration. These data represent the first detailed demonstration of the central role of AQP2 blockade in the aquaretic effect of tolvaptan and underscore a novel effect in raising intracellular calcium that can be of significant clinical relevance.

Treatment for cirrhotic ascites

Common complications of decompensated liver cirrhosis are esophageal varices, hepatic encephalopathy and ascites. After the onset of complications, the prognosis worsens. In patients with ascites, the 5-year mortality rate is 44%. Furthermore, hyponatremia, spontaneous bacterial translocation and hepatorenal syndrome also greatly worsen the prognosis. Effective treatment of cirrhotic ascites improves the quality of life and survival rate. Recently, the newly produced diuretic, tolvaptan (vasopressin V2 receptor antagonist), was reported to be effective in the treatment of refractory ascites in liver cirrhosis; however, there has not been an associated positive effect on the prognosis. There are various types of treatment for ascites, such as large-volume paracenteses, a cell-free and concentrated ascites reinfusion therapy, a transjugular intrahepatic portosystemic shunt, and a peritoneo-venous shunt. Although they improve the prognosis, liver transplantation remains the ultimate form of treatment. The present article discusses the therapeutic management of cirrhotic ascites.

Different Effects of Tolvaptan in Patients with Idiopathic Membranous Nephropathy with Nephrotic Syndrome

This case report discusses the clinical indication for immunosuppressants in patients with idiopathic membranous nephropathy (IMN). Because this disease occasionally shows spontaneous remission, it is necessary to determine the predictive values for a therapeutic effect in order to provide appropriate treatment. Two distinct cases described herein illustrate the different effects of tolvaptan in responders and non-responders, according to the pre-treatment levels of AQP-2 immunostaining in the samples from renal biopsy and urinary levels of AQP-2 and osmolality, suggesting that these values may be useful predictors of response to tolvaptan in patients with nephrotic IMN.

Aquaporins in Cardiovascular System

Recent studies have shown that some aquaporins (AQPs ), including AQP1, AQP4, AQP7 and AQP9, are expressed in endothelial cells, vascular smooth muscle cells and heart of cardiovascular system. These AQPs are involved in the cardiovascular function and in pathological process of related diseases, such as cerebral ischemia , congestion heart failure , hypertension and angiogenesis. Therefore, it is important to understand the accurate association between AQPs and cardiovascular system, which may provide novel approaches to prevent and treat related diseases. Here we will discuss the expression and physiological function of AQPs in cardiovascular system and summarize recent researches on AQPs related cardiovascular diseases.

Disruption of Membranes of Extracellular Vesicles Is Necessary for ELISA Determination of Urine AQP2: Proof of Disruption and Epitopes of AQP2 Antibodies

Aquaporin-2 (AQP2) is present in urine extracellular vesicles (EVs) and is a useful biomarker for water balance disorders. We previously found that pre-treatment of urine with alkali/detergent or storage at −25 °C is required for enzyme-linked immunosorbent assay (ELISA) measurement. We speculated that disruptions of EVs membranes are necessary to allow for the direct contact of antibodies with their epitopes. Human urine EVs were prepared using an ultracentrifugation method. Urine EV samples were stored at different temperatures for a week. Electron microscopy showed abundant EVs with diameters of 20–100 nm, consistent with those of exosomes, in normal urine, whereas samples from alkali/detergent pre-treated urine showed fewer EVs with large swollen shapes and frequent membrane disruptions. The abundance and structures of EVs were maintained during storage at −80 °C, but were severely damaged at −25 °C. Binding and competitive inhibition assays showed that epitopes of monoclonal antibody and polyclonal antibody were the hydrophilic Loop D and C-terminus of AQP2, respectively, both of which are present on the inner surface of EVs. Thus, urine storage at −25 °C or pre-treatment with alkali/detergent disrupt EVs membranes and allow AQP2 antibodies to bind to their epitopes located inside EVs.