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.

Kidney collecting duct-derived vasopressin is not essential for appropriate concentration or dilution of urine.

We have previously shown that kidney collecting ducts make vasopressin. However, the physiological role of collecting duct-derived vasopressin is uncertain. We hypothesized that collecting duct-derived vasopressin is required for the appropriate concentration of urine. We developed a vasopressin conditional knockout (KO) mouse model wherein Cre recombinase expression induces deletion of arginine vasopressin (Avp) exon 1 in the distal nephron. We then used age-matched 8- to 12-wk-old Avp fl/fl;Ksp-Cre(-) [wild type (WT)] and Avp fl/fl;Ksp-Cre(+) mice for all experiments. We collected urine, serum, and kidney lysates at baseline. We then challenged both WT and knockout (KO) mice with 24-h water restriction, water loading, and administration of the vasopressin type 2 receptor agonist desmopressin (1 µg/kg ip) followed by the vasopressin type 2 receptor antagonist OPC-31260 (10 mg/kg ip). We performed immunofluorescence and immunoblot analysis at baseline and confirmed vasopressin KO in the collecting duct. We found that urinary osmolality (UOsm), plasma Na+, K+, Cl-, blood urea nitrogen, and copeptin were similar in WT vs. KO mice at baseline. Immunoblots of the vasopressin-regulated proteins Na+-K+-2Cl- cotransporter, NaCl cotransporter, and water channel aquaporin-2 showed no difference in expression or phosphorylation at baseline. Following 24-h water restriction, WT and KO mice had no differences in UOsm, plasma Na+, K+, Cl-, blood urea nitrogen, or copeptin. In addition, there were no differences in the rate of urinary concentration or dilution as in WT and KO mice UOsm was nearly identical after desmopressin and OPC-31260 administration. We conclude that collecting duct-derived vasopressin is not essential to appropriately concentrate or dilute urine.NEW & NOTEWORTHY Hypothalamic vasopressin is required for appropriate urinary concentration. However, whether collecting duct-derived vasopressin is involved remains unknown. We developed a novel transgenic mouse model to induce tissue-specific deletion of vasopressin and showed that collecting duct-derived vasopressin is not required to concentrate or dilute urine.

Sex differences in the structure and function of the vasopressin system in the ventral pallidum are associated with the sex-specific regulation of social play behavior in juvenile rats.

Vasopressin (AVP) regulates various social behaviors, often in sex-specific ways, including social play behavior, a rewarding behavior displayed primarily by juveniles. Here, we examined whether and how AVP acting in the brain's reward system regulates social play behavior in juvenile rats. Specifically, we focused on AVP signaling in the ventral pallidum (VP), a brain region that is a part of the reward system. First, we examined the organization of the VP-AVP system in juvenile rats and found sex differences, with higher density of both AVP-immunoreactive fibers and AVP V1a receptor (V1aR) binding in males compared to females while females show a greater number of V1aR-expressing cells compared to males. We further found that, in both sexes, V1aR-expressing cells co-express a GABA marker to a much greater extent (approx. 10 times) than a marker for glutamate. Next, we examined the functional involvement of V1aR-expressing VP cells in social play behavior. We found that exposure to social play enhanced the proportion of activated V1aR-expressing VP cells in males only. Finally, we showed that infusion of a specific V1aR antagonist into the VP increased social play behaviors in juvenile male rats while decreasing these behaviors in juvenile female rats. Overall, these findings reveal structural and functional sex differences in the AVP-V1aR system in the VP that are associated with the sex-specific regulation of social play behavior.

Arginine vasopressin in mood disorders: A potential biomarker of disease pathology and a target for pharmacologic intervention.

Vasopressin or arginine-vasopressin (AVP) is a neuropeptide molecule known for its antidiuretic effects and serves to regulate plasma osmolality and blood pressure. The existing literature suggests that AVP plays a multifaceted-though less well-known-role in the central nervous system (CNS), particularly in relation to the pathophysiology and treatment of mood disorders. Animal models have demonstrated that AVP is implicated in regulating social cognition, affiliative and prosocial behaviors, and aggression, often in conjunction with oxytocin. In humans, AVP is implicated in mood disorders through its effects on the hypothalamic-pituitary-adrenal (HPA) axis as well as on the serotoninergic and glutamatergic systems. Measuring plasma AVP has yielded interesting but mixed results in mood and stress-related disorders. Recent advances have led to the development of copeptin as a stable and reliable surrogate biomarker for AVP. Another interesting but relatively unexplored issue is the interaction between the osmoregulatory system and mood disorder pathophysiology, given that psychotropic medications often cause dysregulation of AVP receptor expression or signaling that can subsequently lead to clinical syndromes like syndrome of inappropriate diuresis and diabetes insipidus. Finally, pharmaceutical trials of agents that act on V1a and V1b receptor antagonists are still underway. This narrative review summarizes: (1) the neurobiology of the vasopressinergic system in the CNS; (2) the interaction between AVP and the monoaminergic and glutamatergic pathways in the pathophysiology and treatment of mood disorders; (3) the iatrogenic AVP dysregulation caused by psychotropic medications; and (4) the pharmaceutical development of AVP receptor antagonists for the treatment of mood disorders.

The Vasopressin Receptor Antagonist Tolvaptan Counteracts Tumor Growth in a Murine Xenograft Model of Small Cell Lung Cancer.

We have previously demonstrated that the vasopressin type 2 receptor (AVPR2) antagonist tolvaptan reduces cell proliferation and invasion and triggers apoptosis in different human cancer cell lines. To study this effect in vivo, a xenograft model of small cell lung cancer was developed in Fox1nu/nu nude mice through the subcutaneous inoculation of H69 cells, which express AVPR2. One group of mice (n = 5) was treated with tolvaptan for 60 days, whereas one group (n = 5) served as the control. A reduced growth was observed in the tolvaptan group in which the mean tumor volume was significantly smaller on day 60 compared to the control group. In the latter group, a significantly lower survival was observed. The analysis of excised tumors revealed that tolvaptan effectively inhibited the cAMP/PKA and PI3K/AKT signaling pathways. The expression of the proliferative marker proliferating cell nuclear antigen (PCNA) was significantly lower in tumors excised from tolvaptan-treated mice, whereas the expression levels of the apoptotic marker caspase-3 were higher than those in control animals. Furthermore, tumor vascularization was significantly lower in the tolvaptan group. Overall, these findings suggest that tolvaptan counteracts tumor progression in vivo and, if confirmed, might indicate a possible role of this molecule as an adjuvant in anticancer strategies.

Arginine vasopressin deficiency and conivaptan (a V1a-V2 receptor antagonist) treatment reverses liver damage and fibrosis in rats with chronic portocaval anastomosis.

Arginine vasopressin (AVP) is a naturally occurring hormone synthesized in the hypothalamus. AVP demonstrates pro-fibrotic effects as it stimulates hepatic stellate cells to secrete transforming growth factor-ß (TGF-ß) and collagen. Previous work in liver cirrhotic (CCL4 -induced) hamsters demonstrated that AVP deficiency induced by neurointermediate pituitary lobectomy (NIL) can restore liver function. Therefore, we hypothesized that liver fibrosis would decrease in portocaval anastomosis (PCA) rats, which model chronic liver diseases, when they are treated with the V1a-V2 AVP receptor antagonist conivaptan (CV). In this study, changes in liver histology and gene expression were analysed in five experimental groups: control, PCA, NIL, PCA + NIL and PCA + CV, with NIL surgery or CV treatment administered 8 weeks after PCA surgery. Body weight gain was assessed on a weekly basis, and serum liver function, liver weight and liver glycogen content were assessed following euthanasia. Most PCA-induced phenotypes were reverted to normal levels following AVP-modelled deficiency, though hypoglycemia and ammonium levels remained elevated in the PCA + CV group. Liver histopathological findings showed a significant reversal in collagen content, less fibrosis in the triad and liver septa and increased regenerative nodules. Molecular analyses showed that the expression of fibrogenic genes (TGF-ß and collagen type I) decreased in the PCA + CV group. Our findings strongly suggest that chronic NIL or CV treatment can induce a favourable microenvironment to decrease liver fibrosis and support CV as an alternative treatment for liver fibrosis.

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.

Nutritional Status is Associated With Preserved Kidney Function in Patients With Autosomal Dominant Polycystic Kidney Disease.

OBJECTIVE: Malnutrition is a common complication in autosomal dominant polycystic kidney disease (ADPKD). We examined whether nutritional status is associated with the preservation of kidney function, using a cohort of typical ADPKD. METHODS: We enrolled ambulatory ADPKD patients in 9 tertiary medical centers in Korea from May 2019 to December 2021. We excluded patients who were aged less than 18 years, who had known end-stage kidney disease at the time of enrollment, who had a diagnosis of atypical ADPKD, and who were Tolvaptan users. The primary outcome was an estimated glomerular filtration rate (eGFR) decline >3 mL/min/1.73 m2, based on nutritional status assessed by subjective global assessment (SGA). We also evaluated an eGFR decline >1 mL/min/1.73 m2, an increase in urine protein-creatinine ratio (UPCR) > 0, and an increase in UPCR >0.3 as secondary outcomes, based on SGA after the 1-year follow-up. A logistic regression (LR) model was used to calculate the odds ratio (OR) for the primary outcome. Because there were differences in several baseline variables, such as Mayo classification, serum hemoglobin, serum creatinine, and UPCR between SGA groups, we matched propensity scores. RESULTS: In total, 805 patients were prospectively enrolled. Among them, 236 patients who had 1-year follow-up data and typical imaging findings were analyzed to evaluate the effect of nutritional status on kidney function. SGA was used to assess the nutritional status. The mean age was 45.0 ± 13.3 years, and 49.6% of the patients were female. The mean eGFR was 81.9 mL/min/1.73 m2. Among the 236 patients, 91 (38.6%) experienced a 1-year eGFR decline >3 mL/min/1.73 m2. When a multivariable LR was applied, SGA 3-6 was identified as a significant factor related to a 1-year eGFR decline >3 mL/min/1.73 m2 (adjusted OR = 1.22 [1.04-1.43]; P = .017). Despite matching propensity scores, the 1-year eGFR decline >3 mL/min/1.73 m2 was still higher in the SGA 3-6 group regardless of proteinuria. CONCLUSION: Good nutritional status is associated with better-preserved kidney function in non-obese typical ADPKD patients who do not take Tolvaptan.

Involvement of Vasopressin in Tissue Hypoperfusion during Cardiogenic Shock Complicating Acute Myocardial Infarction in Rats.

Acute heart failure (AHF) due to acute myocardial infarction (AMI) is likely to involve cardiogenic shock (CS), with neuro-hormonal activation. A relationship between AHF, CS and vasopressin response is suspected. This study aimed to investigate the implication of vasopressin on hemodynamic parameters and tissue perfusion at the early phase of CS complicating AMI. Experiments were performed on male Wistar rats submitted or not to left coronary artery ligation (AMI and Sham). Six groups were studied Sham and AMI treated or not with either a vasopressin antagonist SR-49059 (Sham-SR, AMI-SR) or agonist terlipressin (Sham-TLP, AMI-TLP). Animals were sacrificed one day after surgery (D1) and after hemodynamic parameters determination. Vascular responses to vasopressin were evaluated, ex vivo, on aorta. AHF was defined by a left ventricular ejection fraction below 40%. CS was defined by AHF plus tissue hypoperfusion evidenced by elevated serum lactate level or low mesenteric oxygen saturation (SmO2) at D1. Mortality rates were 40% in AMI, 0% in AMI-SR and 33% in AMI-TLP. Immediately after surgery, a sharp decrease in SmO2 was observed in all groups. At D1, SmO2 recovered in Sham and in SR-treated animals while it remained low in AMI and further decreased in TLP-treated groups. The incidence of CS among AHF animals was 72% in AMI or AMI-TLP while it was reduced to 25% in AMI-SR. Plasma copeptin level was increased by AMI. Maximal contractile response to vasopressin was decreased in AMI (32%) as in TLP- and SR- treated groups regardless of ligation. Increased vasopressin secretion occurring in the early phase of AMI may be responsible of mesenteric hypoperfusion resulting in tissue hypoxia. Treatment with a vasopressin antagonist enhanced mesenteric perfusion and improve survival. This could be an interesting therapeutic strategy to prevent progression to cardiogenic shock.

Physiological and pharmacological impact of oxytocin on epididymal propulsion during the ejaculatory process in rodents and men.

During the emission phase of ejaculation, the sperm is driven from the cauda epididymidis, where it is stored, through the vas deferens by strong contractions. These contractions are thought of as being mainly induced by the sympathetic nervous system and the neurotransmitter noradrenaline. In the present study, we investigated the effect of oxytocin (suggested to exert effects during ejaculation as well) on defined segments of the rat and human epididymis using live imaging. Our results indicate that it is the very last part of the epididymis, segment 19 (S19) in rat and likewise segment 9 in human, which responds in a uniquely strong and rapid manner to oxytocin (similar to noradrenaline). Because of the complex nature of this contractile response, we developed an imaging analysis method, which allowed us to quantify multidirectional contractions and to display them using heat maps. The reaction of S19 to oxytocin was concentration-dependent and could be inhibited by pretreatment with oxytocin antagonists (atosiban and cligosiban), but not with an arginine vasopressin 1A antagonist (SR49059). In both rat and human tissue, pretreatment with the alpha-1 adrenoreceptor antagonist tamsulosin inhibited the response to noradrenaline, whereas the effect of oxytocin was unimpaired. Our data (from men and rodents) strongly suggest that the hormone oxytocin is involved in the ejaculatory process. Thus, oxytocin-based medications might be a promising non-adrenergic treatment option for ejaculatory disorders. Additionally, we propose that S19 could be an advantageous model (detecting very low concentrations of oxytocin) to test the bioactivity of new oxytocin agonists and oxytocin antagonists.

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.

Tolvaptan induces body fluid loss and subsequent water conservation in normal rats.

We have recently reported that the urea osmolyte-associated water conservation system is activated in fluid loss models such as high salt-induced natriuresis, renal injury-induced impaired renal concentrating ability, or skin barrier dysfunction-induced transepidermal water loss. The system consists of the interaction of multiple organs including renal urea recycling, hepato-muscular ureagenesis, and suppression of cardiovascular energy expenditure. Here, we determined the effect of pharmacological fluid loss induced by tolvaptan, a selective vasopressin V2 receptor antagonist, on water conservation. We evaluated the water conservation system in rats that consumed a control diet or a diet containing 0.1% tolvaptan. Tolvaptan increased urine volume on day 1, but this renal water loss then gradually decreased. Body water and osmolyte content were decreased by tolvaptan on day 1 but had normalized by day 7. Tolvaptan induced fluid loss on day 1, and the following restoration of body fluid on day 7 was associated with an increase in urea transporter A1-associated renal urea recycling. Tolvaptan did not affect hepato-muscular ureagenesis on day 1 and day 7, or cardiovascular energy expenditure during treatment. Thus, tolvaptan-induced fluid loss leads to activation of the water conservation system via renal urea recycling.

In vitro and in vivo pharmacological profile of OPC-61815, a water-soluble phosphate ester pro-drug of tolvaptan.

Tolvaptan is an orally active vasopressin V2 receptor antagonist and used for the treatment of volume overload in some disease as an aquaretic. Tolvaptan sodium phosphate (OPC-61815) is a pro-drug of tolvaptan that was designed to improve water solubility and enable intravenous use. The conversion of OPC-61815 to tolvaptan was evaluated for in vitro and in vivo pharmacokinetic studies. The pharmacodynamics of OPC-61815 were evaluated for in vitro receptor binding affinity, in vivo aquaretic and anti-edematous action. The solubility of OPC-61815 in water at 25 °C was 72.4 mg/mL and more than 100,000 times the solubility of tolvaptan. OPC-61815 was hydrolyzed to tolvaptan by human tissue S9 fractions and main enzyme of hydrolysis was alkaline phosphatase. After intravenous administration of OPC-61815 to rats and dogs, tolvaptan was detected in plasma within 5 min and the bioavailability of tolvaptan was 57.7% and 50.9%, respectively. Binding affinity of OPC-61815 for the human V2 receptor was 1/14 weaker than that of tolvaptan. OPC-61815 exerted dose-dependent aquaretic action in rats and dogs and a corresponding anti-edematous action in rat edema models. These results suggest that OPC-61815, a water-soluble phosphate ester pro-drug of tolvaptan, is an effective aquaretic by converting to tolvaptan after intravenous administration.

A New Role for Conivaptan in Ulcerative Colitis in Mice: Inhibiting Differentiation of CD4+T Cells into Th1 Cells.

BACKGROUND: Conivaptan, a nonselective antagonist of vasopressin receptors V1a and V2, is the first drug of this class to be used for treating euvolemic and hypervolemic hyponatremia. Recently, increasing evidence supports the involvement of vasopressin in immune responses. AIMS: In this study, we investigated the effect of conivaptan on the modulation of CD4+ T cell homeostasis and the progression of experimental colitis. METHODS: The expression of the V1a receptor on CD4+ T cells was detected by immunofluorescence and western blot. The subset of isolated CD4+ T cells were examined after arginine vasopressin (AVP) incubation. CD4+ T cells were injected into DNBS-induced mice through the tail vein. The severity of colitis was evaluated according to weight, disease activity index (DAI), and morphological injury. Intracellular Ca2+ ([Ca2+]i) signaling in CD4+ T cells was measured using the Fluo-3 AM loading method. T-bet and IFN-γ mRNAs in the colon were detected by real-time polymerase chain reaction (qPCR). RESULTS: We found that CD4+ T cells expressed the V1a receptor. Activation of the V1a receptor significantly promoted the differentiation of CD4+ T cells into T helper 1 (Th1) cells. This process was blocked by conivaptan treatment. However, the activation of the V1a receptor did not evoke an increase in [Ca2+]i in CD4+ T cells. Notably, conivaptan markedly alleviated body weight loss, pathological damage, and expression of T-bet and IFN-γ in the colon of DNBS-treated mice. CONCLUSIONS: For the first time, we report that conivaptan attenuated colitis by inhibiting the differentiation of CD4+ T cells into Th1 cells. Mechanistically, the anti-inflammatory role of conivaptan is independent of [Ca2+]i.

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

PURPOSE: Hyponatremia, the most frequent electrolyte alteration in clinical practice, has been associated with a worse prognosis in cancer patients. On the other hand, a better outcome has been related to serum sodium normalization. In vitro studies have shown that low extracellular sodium promotes cancer cells proliferation and invasiveness. Tolvaptan, a selective vasopressin receptor type 2 (V2) antagonist, has been effectively used in the last decade for the treatment of hyponatremia secondary to the Syndrome of Inappropriate Antidiuresis. A few in vitro data suggested a direct role of tolvaptan in counteracting cancer progression, so far. The aim of this study was to evaluate the effect and the mechanism of action of tolvaptan in cell lines from different tumours [i.e. colon cancer (HCT-8), hepatocarcinoma (HepG2), neuroblastoma (SK-N-AS)]. METHODS AND RESULTS: First, we showed that these cell lines express the V2 receptor. Tolvaptan significantly reduced cell proliferation with an IC50 in the micromolar range. Accordingly, reduced levels of cAMP, of the catalytic α subunit of PKA, and a reduced pAKT/AKT ratio were observed. Tolvaptan effectively inhibited cell cycle progression, whereas it induced apoptotis. Furthermore, it reduced cell invasiveness. In particular, anchorage-independent growth and the activity of collagenases type IV were blunted in the three cell lines. Accordingly, tolvaptan counteracted the RhoA/ROCK1-2 pathway, which has a pivotal role in regulating cell movement. CONCLUSIONS: Overall, these findings indicate that tolvaptan effectively inhibits tumour progression in vitro. Further studies should clarify whether the V2 receptor might be considered a possible target in anti-cancer strategies in the future.

Initial decline in eGFR to predict tolvaptan response in autosomal-dominant polycystic kidney disease.

BACKGROUND: Tolvaptan, a vasopressin V2 receptor antagonist, is used to treat autosomal-dominant polycystic kidney disease (ADPKD). Although tolvaptan curbs disease progression, a few reports have examined factors related to treatment response. The estimated glomerular filtration rate (eGFR) decreases soon after tolvaptan is initiated. We investigated whether initial eGFR decline affects renal prognosis of patients. METHODS: This was a single-center, retrospective observational cohort study. Eighty-three patients with ADPKD who initiated tolvaptan were selected. We analyzed the relationship of the initial eGFR change with clinical parameters and analyzed the annual eGFR change in terms of renal prognostic value using univariable and multivariable linear regression analyses. RESULTS: The initial eGFR change was - 4.6 ± 8.0%/month. The initial eGFR change correlated significantly with the annual eGFR change in multivariable analysis, suggesting that the larger decline in the initial eGFR change, the better the renal prognosis. Furthermore, the change in fractional excretion (FE) of free water (FEH2O) correlated positively with initial eGFR change. FEH2O and urea nitrogen FE (FEUN) increased significantly; however, sodium FE (FENa) level remained unchanged. In approximately half of the patients, FENa unexpectedly decreased. CONCLUSIONS: The initial eGFR decline might be caused by suppressing glomerular hyperfiltration, due to the pharmacological effect of tolvaptan, and/or by reducing renal plasma flow, due to potential volume depletion. The initial eGFR change reflects the tolvaptan effect, can be easily evaluated in clinical practice, and may be useful as one of the clinical indicator for predicting renal prognosis in patients under tolvaptan.

A Shared Nephroprotective Mechanism for Renin-Angiotensin-System Inhibitors, Sodium-Glucose Co-Transporter 2 Inhibitors, and Vasopressin Receptor Antagonists: Immunology Meets Hemodynamics.

A major paradigm in nephrology states that the loss of filtration function over a long time is driven by a persistent hyperfiltration state of surviving nephrons. This hyperfiltration may derive from circulating immunological factors. However, some clue about the hemodynamic effects of these factors derives from the effects of so-called nephroprotective drugs. Thirty years after the introduction of Renin-Angiotensin-system inhibitors (RASi) into clinical practice, two new families of nephroprotective drugs have been identified: the sodium-glucose cotransporter 2 inhibitors (SGLT2i) and the vasopressin receptor antagonists (VRA). Even though the molecular targets of the three-drug classes are very different, they share the reduction in the glomerular filtration rate (GFR) at the beginning of the therapy, which is usually considered an adverse effect. Therefore, we hypothesize that acute GFR decline is a prerequisite to obtaining nephroprotection with all these drugs. In this study, we reanalyze evidence that RASi, SGLT2i, and VRA reduce the eGFR at the onset of therapy. Afterward, we evaluate whether the extent of eGFR reduction correlates with their long-term efficacy. The results suggest that the extent of initial eGFR decline predicts the nephroprotective efficacy in the long run. Therefore, we propose that RASi, SGLT2i, and VRA delay kidney disease progression by controlling maladaptive glomerular hyperfiltration resulting from circulating immunological factors. Further studies are needed to verify their combined effects.

Vasopressin Receptor Type-2 Mediated Signaling in Renal Cell Carcinoma Stimulates Stromal Fibroblast Activation.

Vasopressin type-2 receptor (V2R) is ectopically expressed and plays a pathogenic role in clear cell renal cell carcinoma (ccRCC) tumor cells. Here we examined how V2R signaling within human ccRCC tumor cells (Caki1 cells) stimulates stromal cancer-associated fibroblasts (CAFs). We found that cell culture conditioned media from Caki1 cells increased activation, migration, and proliferation of fibroblasts in vitro, which was inhibited by V2R gene silencing in Caki1 cells. Analysis of the conditioned media and mRNA of the V2R gene silenced and control Caki1 cells showed that V2R regulates the production of CAF-activating factors. Some of these factors were also found to be regulated by YAP in these Caki1 cells. YAP expression colocalized and correlated with V2R expression in ccRCC tumor tissue. V2R gene silencing or V2R antagonist significantly reduced YAP in Caki1 cells. Moreover, the V2R antagonist reduced YAP expression and myofibroblasts in mouse xenograft tumors. These results suggest that V2R plays an important role in secreting pro-fibrotic factors that stimulate fibroblast activation by a YAP-dependent mechanism in ccRCC tumors. Our results demonstrate a novel role for the V2R-YAP axis in the regulation of myofibroblasts in ccRCC and a potential therapeutic target.

V1a and V1b vasopressin receptors within the paraventricular nucleus contribute to hypertension in male rats exposed to chronic mild unpredictable stress.

Depression is an independent nontraditional risk factor for cardiovascular disease and mortality. The chronic unpredictable mild stress (CMS) rat model is a validated model of depression. Within the paraventricular nucleus (PVN), vasopressin (VP) via V1aR and V1bR have been implicated in stress and neurocardiovascular dysregulation. We hypothesized that in conscious, unrestrained CMS rats versus control, unstressed rats, PVN VP results in elevated arterial pressure (MAP), heart rate, and renal sympathetic nerve activity (RSNA) via activation of V1aR and/or V1bR. Male rats underwent 4 wk of CMS or control conditions. They were then equipped with hemodynamic telemetry transmitters, PVN cannula, and left renal nerve electrode. V1aR or V1bR antagonism dose-dependently inhibited MAP after VP injection. V1aR or V1bR blockers at their ED50 doses did not alter baseline parameters in either control or CMS rats but attenuated the pressor response to VP microinjected into PVN by ∼50%. Combined V1aR and V1bR inhibition completely blocked the pressor response to PVN VP in control but not CMS rats. CMS rats required combined maximally inhibitory doses to block either endogenous VP within the PVN or responses to microinjected VP. Compared with unstressed control rats, CMS rats had higher plasma VP levels and greater abundance of V1aR and V1bR transcripts within PVN. Thus, the CMS rat model of depression results in higher resting MAP, heart rate, and RSNA, which can be mitigated by inhibiting vasopressinergic mechanisms involving both V1aR and V1bR within the PVN. Circulating VP may also play a role in the pressor response.

Vasopressin V1B Receptor Antagonists as Potential Antidepressants.

Accumulating evidence shows that certain populations of depressed patients have impaired hypothalamus-pituitary-adrenal (HPA) axis function. Arginine-vasopressin (AVP) is one of the primary factors in HPA axis regulation under stress situations, and AVP and its receptor subtype (V1B receptor) play a pivotal role in HPA axis abnormalities observed in depression. Based on this hypothesis, several non-peptide V1B receptor antagonists have been synthesized, and the efficacies of some V1B receptor antagonists have been investigated in both animals and humans. V1B receptor antagonists exert antidepressant-like effects in several animal models at doses that attenuate the hyperactivity of the HPA axis, and some of their detailed mechanisms have been delineated. These results obtained in animal models were, at least partly, reproduced in clinical trials. At least 2 V1B receptor antagonists (TS-121 and ABT-436) showed tendencies to reduce the depression scores of patients with major depressive disorder at doses that attenuate HPA axis hyperactivity or block the pituitary V1B receptor. Importantly, TS-121 showed a clearer efficacy for patients with higher basal cortisol levels than for those with lower basal cortisol levels, which was consistent with the hypothesis that V1B receptor antagonists may be more effective for patients with HPA axis hyperactivity. Therefore, V1B receptor antagonists are promising approaches for the treatment of depression involving HPA axis impairment such as depression.