Vasopressin Type Research Articles

Pharmacoperone rescue of vasopressin 2 receptor mutants reveals unexpected constitutive activity and coupling bias.

Pharmacoperones are small molecules that diffuse into cells and rescue misfolded, mistrafficked protein mutants, restoring their function. These substances act with high target specificity, serving as templates to fold (or refold) receptors, enzymes, ion channels or other proteins and enable them to pass the scrutiny of the cellular quality control system (“rescue”). In the present study we demonstrate that a rescued mutant (L83Q) of the vasopressin type 2 receptor (V2R), shows a strong bias for Gs coupling unlike the WT V2 receptor, which couples to both Gs and Gq/11. Failure of the mutant to couple to Gq/11 was not due to a limiting quantity of G-proteins since other Gq/11-coupled receptors (WT V2R, histamine receptor and muscarinic receptor) responded appropriately to their ligands. Transfection with DNA encoding Gq enabled the V2 receptor mutant to couple to this G protein, but only modestly compared with the WT receptor. Fourteen V2R mutant pharmacoperones, of multiple chemical classes, obtained from a high throughput screen of a 660,000 structure library, and one V2R peptidomimetic antagonist rescues L83Q. The rescued mutant shows similar bias with all pharmacoperones identified, suggesting that the bias is intrinsic to the mutant protein’s structure, rather than due to the chemical class of the pharmacoperone. In the case of V2R mutant Y128S, rescue with a pharmacoperone revealed constitutive activity, also with bias for Gs, although both IP and cAMP were produced in response to agonist. These results suggest that particular rescued receptor mutants show functional characteristics that differ from the WT receptor; a finding that may be important to consider as pharmacoperones are developed as therapeutic agents.

A case of nephrogenic syndrome of inappropriate antidiuresis caused by a mutation of the vasopressin type 2 receptor

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare X-linked disorder of water balance, which was first described in two unrelated male infants with severe symptomatic hyponatremia. NSIAD is caused by activating mutations of the arginine vasopressin receptor 2 (AVPR2) gene, resulting in impaired reabsorption of free water, which leads to increased osmolarity of urine, plasma hypo-osmolarity, and persistent hyponatremia. We report, for the first time in the domestic literature, a case of isolated euvolemic hyposmolality hyponatremia in a child with oligodipsia. Because hypocorticism and renal pathology were excluded, and there was no antidiuretic hormone hypersecretion, NSIAD was suggested. A molecular genetic study revealed a new mutation L312S, not described earlier, in the seventh transmembrane domain of the AVPR2 gene. Pathogenicity of the mutation was proved by a functional study. We provide the clinical and laboratory characteristics of SIAD and the main principles of treatment. This disease should be considered in the differential diagnosis of hyponatremia syndrome.

Prediction of diuretic response to tolvaptan by a simple, readily available spot urine Na/K ratio.

BackgroundTolvaptan is vasopressin type 2 receptor antagonist that inhibits water reabsorption. It is used in combination with standard diuretics to treat ascites unresponsive to standard diuretic therapy or hyponatremia because of liver cirrhosis. This study evaluated the effectiveness and safety of tolvaptan in clinical practice and aimed to determine the factors related to its effectiveness.MethodsTolvaptan was administered to 88 consecutive cirrhotic patients with ascites unresponsive to standard diuretic therapy. An effective treatment response was a ≥2% reduction in body weight on day 7. The association of patient pretreatment characteristics with therapeutic effects was analyzed.ResultsMean weight reduction on day 7 of tolvaptan therapy was −2.9% ± 3.2%, and treatment was effective in 52% of patients. Multivariate analysis revealed that spot urine Na/K ratio ≥2.5 at baseline was the only factor independently related to therapeutic effect, with an odds ratio of 7.85 (95% confidence interval 2.64–23.40, p = 0.0002). Weight reduction percentage on day 7 was −4.0% ± 2.8% in patients with spot urine Na/K ≥2.5, which was significantly greater than the 0.7% ± 2.7% loss in those with urine Na/K < 2.5 (p < 0.05). A spot urine Na/K ratio ≥2.5 had a sensitivity of 85% and specificity of 60% for predicting effective treatment. No adverse events of treatment led to treatment discontinuation.ConclusionsBaseline spot urine Na/K was predictive of an effective response to tolvaptan therapy. It is simple to perform and readily available and might serve as an indicator of optimal timing of tolvaptan administration in patients with inadequate response to conventional Na diuretic therapy.

Effectiveness and safety of tolvaptan in liver cirrhosis patients with edema: Interim results of post-marketing surveillance of tolvaptan in liver cirrhosis (START study).

Loop diuretics and spironolactone are used in patients with hepatic edema, but they are sometimes associated with insufficient responses as well as adverse events. Tolvaptan, a vasopressin type 2 receptor antagonist, was approved for hepatic edema in 2013. A large-scale post-marketing surveillance study has been carried out to evaluate the effectiveness and safety of tolvaptan in real-world clinical settings. Patients with hepatic cirrhosis with insufficient response to conventional diuretics were enrolled. The observational period was up to 6months. Changes in body weight and clinical symptoms were measured to evaluate effectiveness. The incidence of adverse drug reactions was summarized as a safety measure. Of 970 patients enrolled, 463 were included in the safety analysis. Of this group, 340 were included in the effectiveness analysis. Decreases in body weight from baseline were -2.38kg on day 7 and -3.52kg on day 14. Ascites and bloated feeling was significantly improved within 14days. The mean change in body weight depended on estimated glomerular filtration rate levels. The most frequently reported adverse drug reaction was thirst (6.9% of patients). Serum sodium level of ≥146mEq/L was observed in 12 patients (2.7%). In the real-world clinical setting, tolvaptan showed aquaretic effectiveness in patients with cirrhosis. The mean change in body weight depended on renal function. We recommend tolvaptan use for hepatic cirrhosis at a stage in which the renal function is maintained.

Mechanisms of Diuresis for Acute Decompensated Heart Failure by Tolvaptan.

Tolvaptan, a vasopressin type 2 receptor antagonist, does not affect kidney circulation or cause worsening of renal function (WRF) in patients with acute decompensated heart failure (ADHF). Bioelectrical impedance analysis (BIA) can be used to evaluate intravascular volume by calculating the ratio of extracellular water (ECW) to intracellular water (ICW). There have been no reports examining the mechanisms of tolvaptan-induced diuresis using BIA. We investigated whether tolvaptan decreases excess volume while maintaining intravascular volume in ADHF patients.Study patients included 29 ADHF patients (age 48-95, men 69%) diagnosed between April 2013 and May 2016 and who underwent BIA before and after treatment. Fifteen patients were treated with tolvaptan in addition to conventional diuresis therapy (tolvaptan group), and 14 patients were treated with conventional diuresis therapy only (control group). In the control group, the numerical value of serum creatinine (Cre) significantly increased from 0.89 ± 0.22 mg/ dL to 1.07 ± 0.29 mg/dL (P = 0.004), and the ECW/ICW significantly decreased from 0.696 ± 0.036 to 0.673 ± 0.032 (P = 0.004). These values were not significantly different from those obtained for the tolvaptan group. Furthermore, regression analysis showed a negative correlation between ΔCre and ΔECW/ICW, which are the differences between values before and after treatment (ΔCre = -0.002-5.668 × ΔECW/ICW, r2 = 0.306, P = 0.002).Our findings suggest that WRF is caused by a reduction in intravascular volume and that tolvaptan treatment can decrease the excess volume while maintaining intravascular volume.

Experience with long-term administration of tolvaptan to patients with acute decompensated heart failure.

Tolvaptan (TLV) is an oral selective vasopressin type 2 receptor antagonist. Long-term use of TLV is not recommended in patients with heart failure (HF) if fluid retention disappears and/or body weight is within the target range. However, some patients require long-term use of TLV. The current study investigated the efficacy and safety of long-term use of TLV. Subjects were 258 consecutive patients with HF who received TLV during hospitalization from January 2011 to March 2015. The rate of continuing administration of TLV was evaluated. Moreover, the one-year mortality rate and rate of re-hospitalization either with or without TLV were investigated. Results at discharge and one year later were compared for patients who continued to receive TLV one year after discharge. Oral concomitant medications, blood pressures, heart rate, blood tests, chest X-ray and transthoracic echocardiography were investigated. In-hospital and one-year mortality rates were 15.9% and 27.8%, respectively. Moreover, the mortality rate and/or rate of re-hospitalization within one year was 54.4%. The rate of re-hospitalization for HF was significantly higher in patients who continued to receive TLV after discharge compared to patients who ceased receiving TLV after discharge (p < 0.001). However, the subjects who continued to receive TLV for up to one year after discharge tended to have a longer duration until re-hospitalization for HF and significantly decreased brain natriuretic peptide levels (577.6 ± 528.5 pg/mL to 397.3 ± 365.8 pg/mL, p = 0.015). Long-term use of TLV might delay re-hospitalization for HF in patients with severe HF. Large-scale clinical studies are necessary to verify these results.

Wnt5a induces renal AQP2 expression by activating calcineurin signalling pathway.

Heritable nephrogenic diabetes insipidus (NDI) is characterized by defective urine concentration mechanisms in the kidney, which are mainly caused by loss-of-function mutations in the vasopressin type 2 receptor. For the treatment of heritable NDI, novel strategies that bypass the defective vasopressin type 2 receptor are required to activate the aquaporin-2 (AQP2) water channel. Here we show that Wnt5a regulates AQP2 protein expression, phosphorylation and trafficking, suggesting that Wnt5a is an endogenous ligand that can regulate AQP2 without the activation of the classic vasopressin/cAMP signalling pathway. Wnt5a successfully increases the apical membrane localization of AQP2 and urine osmolality in an NDI mouse model. We also demonstrate that calcineurin is a key regulator of Wnt5a-induced AQP2 activation without affecting intracellular cAMP level and PKA activity. The importance of calcineurin is further confirmed with its activator, arachidonic acid, which shows vasopressin-like effects underlining that calcineurin activators may be potential therapeutic targets for heritable NDI.

Vasopressin type1A receptor deletion enhances cardiac contractility, β-adrenergic receptor sensitivity and acute cardiac injury-induced dysfunction.

Vasopressin type1A receptor (V1AR) expression is elevated in chronic human heart failure (HF) and contributes to cardiac dysfunction in animal models, in part via reduced β-adrenergic receptor (βAR) responsiveness. Although cardiac V1AR overexpression and V1AR stimulation are each sufficient to decrease βAR activity, it is unknown whether V1AR inhibition conversely augments βAR responsiveness. Further, although V1AR has been shown to contribute to chronic progression of HF, its impact on cardiac function following acute ischaemic injury has not been reported. Using V1AR knockout (V1AR KO) mice we assessed the impact of V1AR deletion on cardiac contractility at baseline and following ischaemic injury, βAR sensitivity and cardiomyocyte responsiveness to βAR stimulation. Strikingly, baseline cardiac contractility was enhanced in V1AR KO mice and they experienced a greater loss in contractile function than control mice following acute ischaemic injury, although the absolute levels of cardiac dysfunction and survival rates did not differ. Enhanced cardiac contractility in V1AR KO mice was associated with augmented β-blocker sensitivity, suggesting increased basal βAR activity, and indeed levels of left ventricular cAMP, as well as phospholamban (PLB) and cardiac troponin I (cTnI) phosphorylation were elevated compared with control mice. At the cellular level, myocytes isolated from V1AR KO mice demonstrated increased responsiveness to βAR stimulation consistent with the finding that acute pharmacological V1AR inhibition enhanced βAR-mediated contractility in control myocytes. Therefore, although V1AR deletion does not protect the heart from the rapid development of cardiac dysfunction following acute ischaemic injury, its effects on βAR activity suggest that acute V1AR inhibition could be utilized to promote myocyte contractile performance.

Predictive factors for responders to tolvaptan in fluid management after cardiovascular surgery

ObjectiveTo identify the predictive factors for responders to tolvaptan, a novel vasopressin type 2 receptor antagonist for fluid management after cardiovascular surgery.MethodsBetween January 2013 and May 2014, 113 patients were treated with tolvaptan for fluid management after cardiovascular surgery. As indicators for the effects of tolvaptan, change in bodyweight during the tolvaptan administration period and correlations with perioperative factors were assessed. Thirty-one patients were administered tolvaptan at the first day after surgery (early tolvaptan group). In this group, urine volume during the 6 h before the initial tolvaptan administration was compared with that at 6 h after administration.ResultsFor all the patients, the change in bodyweight during the tolvaptan administration period significantly correlated with pre-operative serum creatinine (r = 0.19, p = 0.04) and albumin levels before tolvaptan administration (r = −0.29, p = 0.002). In the early tolvaptan group, the ratio of urine volume at 6 h before and 6 h after the initial tolvaptan administration significantly correlated with the pre-operative serum creatinine level (r = 0.43, p = 0.02), the serum albumin level before tolvaptan administration (r = −0.50, p = 0.004), and change in bodyweight (r = 0.38, p = 0.03).ConclusionsIn patients undergoing cardiovascular surgery, deteriorating renal function, increased bodyweight, and hypoalbuminemia were found to be predictive factors for responders to tolvaptan for postoperative fluid management.

Tolvaptan for Heart Failure, Systematic Review and Meta-Analysis of Trials.

The vasopressin type 2 receptor antagonist tolvaptan (TLV) is available to treat congestion in patients with heart failure. However, there is paucity of evidence guiding its use, and lack of evidence of its long-term efficacy. Our objectives are to perform a systematic review of studies examining the effects of TLV in patients with heart failure; and a quantitative meta-analysis comparing primary and secondary outcomes between TLV and placebo. Only double-blinded randomized controlled trials, with no restriction on the language or the time of publication, were included. Our main outcome measures were all-cause mortality, change in body weight, change in urine volume, and change in serum sodium. Extracted summary estimates included mean difference and SD for change in body weight, change in urine volume and change in serum sodium levels, and hazard ratio with 95% confidence interval for all-cause mortality. We found 8 double-blinded randomized controlled trials, seven of which were included in this meta-analysis. Assessment of risk of bias was conducted by investigating random sequence generation, allocation concealment, blinding, completeness of outcome data, and potential for selective reporting. We found no evidence of significant bias. TLV showed benefits in reducing body weight, increasing urine volume, and increasing serum sodium. No reduction in mortality was detected. However, the subgroup of patients with hyponatremia might have better mortality outcome with TLV. TLV seemed to be safe, as it did not cause worsening of the renal function or hypotension. In conclusion, a meta-analysis of the published literature suggests short-term benefits of TLV. However, the impact on mortality is inconclusive.

Prognostic Impact of Change in Tolvaptan Usage across the Years for the Treatment of Heart Failure

Background: Tolvaptan, a vasopressin type 2 receptor antagonist, has an aquaretic effect. Because of its beneficial effect on decongestion, the use of tolvaptan for heart failure is increasing and seems to become more active. Here, we assessed the change in tolvaptan usage across the years for the treatment of acute decompensated heart failure (ADHF). Methods and Results: Until December 2015, tolvaptan was used for 254 patients with ADHF. We compared the patients who were administered tolvaptan in the early period until December 2013 (n = 68, E group) with those who were administered tolvaptan in the late period after December 2015 (n = 186, L group). There was no difference between 2 groups in age, gender, systolic function, and kidney function. However, serum sodium levels were lower and the dosage of concomitant loop diuretics was higher in E group than those in L group. Furthermore, in E group, period from admission to tolvaptan start was significantly longer. Kaplan-Meier analysis revealed that cardiac death or rehospitalization for heart failure was significantly lower in L group compared with E group (Log-rank P = .014). Conclusions: In patients with ADHF, tolvaptan usage is becoming earlier. Accumulated experience of treatment with tolvaptan and its appropriate use might improve the outcome in patients with heart failure.

Identification of Potential Pharmacoperones Capable of Rescuing the Functionality of Misfolded Vasopressin 2 Receptor Involved in Nephrogenic Diabetes Insipidus

Pharmacoperones correct the folding of otherwise misfolded protein mutants, restoring function (i.e., providing “rescue”) by correcting their trafficking. Currently, most pharmacoperones possess intrinsic antagonist activity because they were identified using methods initially aimed at discovering such functions. Here, we describe an ultra-high-throughput homogeneous cell-based assay with a cAMP detection system, a method specifically designed to identify pharmacoperones of the vasopressin type 2 receptor (V2R), a GPCR that, when mutated, is associated with nephrogenic diabetes insipidus. Previously developed methods to identify compounds capable of altering cellular trafficking of V2R were modified and used to screen a 645,000 compound collection by measuring the ability of library compounds to rescue a mutant hV2R [L83Q], using a cell-based luminescent detection system. The campaign initially identified 3734 positive modulators of cAMP. The confirmation and counterscreen identified only 147 of the active compounds with an EC50 of ≤5 µM. Of these, 83 were reconfirmed as active through independently obtained pure samples and were also inactive in a relevant counterscreen. Active and tractable compounds within this set can be categorized into three predominant structural clusters, described here, in the first report detailing the results of a large-scale pharmacoperone high-throughput screening campaign.

O4-3 - Effect on Survival of Treatment for Heart Failure with Tolvaptan in Addition to Low Dose Furosemide vs. High Dose Furosemide

Background: The vasopressin type 2 receptor antagonist tolvaptan (TLV) is available to treat congestion in patients with heart failure. However, it is unknown that the proper dose of furosemide which TLV is added to. Method: We enrolled consecutive 124 patients were admitted to our hospital for acute decompensated heart failure in 2015. They began TLV in addition to standard therapy. Patients were divided into 2 groups according to doses of furosemide when TLV therapy was begun. Low dose furosemide group was defined as doses of daily furosemide was under 40 mg and high dose furosemide group was defined as over 40 mg. The primary endpoint was the rate of all cause death. Result: All cause death occurred in 10 of 71 patients (14.0%) in low dose furosemide group and 22 of 53 patients (41.5%) in high dose furosemide group. The risk of all cause death was decreased in low dose furosemide group compared with high dose furosemide group (hazard ratio, 0.29; 95% confidence interval, 0.13–0.60 at univariable analysis; and hazard ratio, 0.28; 95% confidence interval, 0.12–0.59 at multivariable analysis). Conclusion: We suggest that TLV is added to low doses of furosemide.

The vasopressin type 2 receptor and prostaglandin receptors EP2 and EP4 can increase aquaporin-2 plasma membrane targeting through a cAMP-independent pathway.

Apical membrane targeting of the collecting duct water channel aquaporin-2 (AQP2) is essential for body water balance. As this event is regulated by Gs coupled 7-transmembrane receptors such as the vasopressin type 2 receptor (V2R) and the prostanoid receptors EP2 and EP4, it is believed to be cAMP dependent. However, on the basis of recent reports, it was hypothesized in the current study that increased cAMP levels are not necessary for AQP2 membrane targeting. The role and dynamics of cAMP signaling in AQP2 membrane targeting in Madin-Darby canine kidney and mouse cortical collecting duct (mpkCCD14) cells was examined using selective agonists against the V2R (dDAVP), EP2 (butaprost), and EP4 (CAY10580). During EP2 stimulation, AQP2 membrane targeting continually increased during 80 min of stimulation; whereas cAMP levels reached a plateau after 10 min. EP4 stimulation caused a rapid and transient increase in AQP2 membrane targeting, but did not significantly increase cAMP levels. After washout of the EP2 agonist or dDAVP, AQP2 membrane abundance remained elevated for at least 80 min, whereas cAMP levels rapidly decreased. Similar effects of the EP2 agonist were also observed for AQP2 constitutively nonphosphorylated at ser-269. The adenylyl cyclase inhibitor SQ22536 did not prevent AQP2 targeting during stimulation of each receptor, nor after dDAVP washout. In conclusion, this study demonstrates that although direct stimulation with cAMP causes AQP2 membrane targeting, cAMP is not necessary for receptor-mediated AQP2 membrane targeting and Gs-coupled receptors can also signal through an alternative pathway that increases AQP2 membrane targeting.

Metformin improves urine concentration in rodents with nephrogenic diabetes insipidus.

Urine concentration is regulated by vasopressin. Congenital nephrogenic diabetes insipidus (NDI) is caused by vasopressin type 2 receptor (V2R) mutations. We studied whether metformin could improve urine concentration in rodent models of congenital NDI by stimulating AMPK. To block the V2R in rats, tolvaptan (10 mg/kg/d) was given by oral gavage with or without metformin (800 mg/ kg/d). Control rats received vehicle with or without metformin. Tamoxifen-induced V2R KO mice were given metformin (600 mg/kg) or vehicle twice daily. Urine osmolality in tolvaptan-treated rats (1,303 ± 126 mOsM) was restored to control levels by metformin (2,335 ± 273 mOsM) within 3 days and was sustained for up to 10 days. Metformin increased protein abundance of inner medullary urea transporter UT-A1 by 61% and aquaporin 2 (AQP2) by 44% in tolvaptan-treated rats, and immunohistochemistry showed increased membrane accumulation of AQP2 with acute and chronic AMPK stimulation. Outer medullary Na+-K+-2Cl- cotransporter 2 (NKCC2) abundance increased (117%) with AMPK stimulation in control rats but not in V2R-blocked rats. Metformin increased V2R KO mouse urine osmolality within 3 hours, and the increase persisted for up to 12 hours. Metformin increased AQP2 in the V2R KO mice similar to the tolvaptan-treated rats. These results indicate that AMPK activators, such as metformin, might provide a promising treatment for congenital NDI.

Long-term administration of tolvaptan increases myocardial remodeling and mortality via exacerbation of congestion in mice heart failure model after myocardial infarction

BackgroundIn contrast to loop diuretics, tolvaptan does not cause neurohormonal activation in several animal heart failure models. However, it remains unknown whether chronic vasopressin type 2 receptor blockade exerts beneficial effects on mortality in murine heart failure after myocardial infarction (MI). In an experimental heart failure model, we tested the hypothesis that tolvaptan reduces myocardial remodeling and mortality. Methods and resultsMI was induced in 9-week-old male C57Bl6/J by the left coronary artery ligation. In study 1, animals were randomly assigned to treatment with placebo or tolvaptan starting 14days post-MI. In study 2, animals were randomized to tolvaptan or furosemide+tolvaptan starting 14days post-MI. Interestingly, results showed lower survival rate in tolvaptan group compared to placebo. Tolvaptan group had higher serum osmolality, heavier body weight, more severe myocardial remodeling, and lung congestion at day 28 of drug administration compared to placebo. In study 2, addition of furosemide significantly reduced mortality rate seen with tolvaptan, and presented with decreased osmolality, myocardial remodeling, and lung congestion compared to tolvaptan-treated mice. Increase in proximal tubular expression of aquaporin 1, Angiotensin II, and vasopressin seen with tolvaptan treatments were normalized to basal levels, similar to levels in placebo-treated mice. ConclusionsContrary to our hypothesis, tolvaptan was associated with increased mortality in murine heart failure after MI. This increase in lung congestion, myocardial remodeling, could be prevented by co-administration of furosemide, which resulted in normalized serum osmolality, neurohormonal activation, and renal aquaporin 1 expression, and hence decreased mortality post-MI.

Mutations of Vasopressin Receptor 2 Including Novel L312S Have Differential Effects on Trafficking.

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a genetic disease first described in 2 unrelated male infants with severe symptomatic hyponatremia. Despite undetectable arginine vasopressin levels, patients have inappropriately concentrated urine resulting in hyponatremia, hypoosmolality, and natriuresis. Here, we describe and functionally characterize a novel vasopressin type 2 receptor (V2R) gain-of-function mutation. An L312S substitution in the seventh transmembrane domain was identified in a boy presenting with water-induced hyponatremic seizures at the age of 5.8 years. We show that, compared with wild-type V2R, the L312S mutation results in the constitutive production of cAMP, indicative of the gain-of-function NSIAD profile. Interestingly, like the previously described F229V and I130N NSIAD-causing mutants, this appears to both occur in the absence of notable constitutive β-arrestin2 recruitment and can be reduced by the inverse agonist Tolvaptan. In addition, to understand the effect of various V2R substitutions on the full receptor “life-cycle,” we have used and further developed a bioluminescence resonance energy transfer intracellular localization assay using multiple localization markers validated with confocal microscopy. This allowed us to characterize differences in the constitutive and ligand-induced localization and trafficking profiles of the novel L312S mutation as well as for previously described V2R gain-of-function mutants (NSIAD; R137C and R137L), loss-of-function mutants (nephrogenic diabetes insipidus; R137H, R181C, and M311V), and a putative silent V266A V2R polymorphism. In doing so, we describe differences in trafficking between unique V2R substitutions, even at the same amino acid position, therefore highlighting the value of full and thorough characterization of receptor function beyond simple signaling pathway analysis.

Single‐Dose Interaction Study of the Arginine Vasopressin Type 1B Receptor Antagonist ABT‐436 and Alcohol in Moderate Alcohol Drinkers

ABT-436, a potent and selective arginine vasopressin (AVP) type 1B receptor (V1B ) antagonist, has previously demonstrated basal hypothalamic-pituitary-adrenal (HPA) axis attenuation in man. A V1B antagonist is hypothesized as an alcohol-dependent treatment based on the role of the V1B receptor in stress regulation and the finding that stress is a trigger for relapse in alcoholics. A V1B antagonist has shown favorable effects in rat models of alcohol dependence. A single-dose clinical study was conducted to assess the potential for pharmacokinetic or pharmacodynamic interaction between ABT-436 and alcohol. Twenty moderate alcohol drinkers each received the 4 possible combinations of a single 1,000 mg ABT-436 dose (or matching placebo) and a single 0.5 g/kg alcohol dose (or placebo for alcohol) in a double-blind, randomized, 4-period crossover study. Plasma ABT-436 and blood alcohol levels were measured to assess pharmacokinetic interactions. A computerized cognitive test battery (CDR System), Bond-Lader Visual Analog Scales scales, and a postural stability test were used to measure the effects of alcohol and the potential interaction with ABT-436. The pharmacologic effect of ABT-436 was assessed by measuring serum cortisol. Neither ABT-436 nor alcohol affected the blood levels of the other. Alcohol reduced performance on 2 of 5 CDR System composite variables (power of attention, p = 0.002; quality of secondary episodic memory, p < 0.001), and decreased postural stability (p = 0.043). ABT-436 did not exacerbate those deleterious effects. ABT-436 reduced serum cortisol (p < 0.001), and alcohol did not significantly diminish this expected effect on the HPA axis. No pharmacokinetic or pharmacodynamic interaction between ABT-436 and alcohol was observed.

Optimization of Vasopressin Type 2 Receptor Expression in Escherichia coli BL21

Background: Vasopressin type 2 receptor (V 2 R) is a G-protein-coupled receptor (GPCRs) located in nephrons mediating water reabsorption in kidneys. Vasopressin acts at these receptors to enhance water reabsorption in the kidneys while by acting on V1 receptors in blood vessels increases blood pressure. To study V 2 R better, it must be produced in high quantities. Objectives: The current study aimed to optimize expression of V 2 R in Escherichia coli. Materials and Methods: In this investigation, V 2 R gene was cloned in E. coli. The recombinant plasmid pEt15b/V 2 R (rpET-BL21) was transformed into competent E. coli strain BL21 (DE3) cells. Overnight culture of the transformed bacteria was induced by the addition of isopropyl-thio-β-D-galactoside (IPTG). The effects of different IPTG concentrations, temperatures and sampling times on the expression of V 2 R were examined. Samples were analyzed by SDS-PAGE. Results: The maximum amount of protein production was obtained by the addition of 0.75 mM IPTG at 37°C after three hours. The most important factor was harvesting time with P value < 0.0001. In statistical analysis of data, the normal plot shows the normality of distribution of the studentized data. Conclusions: Full factorial design experimental approach helped to identify the critical culture condition parameters in heterologous expression of V 2 R. It would allow studying the parameters affecting the function of this protein in future experiments.

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

Aquaporin-2, a member of the aquaporin family, is an arginine vasopressin-regulated water channel expressed in the renal collecting duct, and a promising marker of the concentrating and diluting ability of the kidney. The arginine vasopressin type-2 antagonist, tolvaptan, is a new-generation diuretic; it is especially indicated in patients with decompensated heart failure refractory to conventional diuretics. However, the ideal responders to tolvaptan have not yet been identified, and non-responders experience worse clinical courses despite treatment with tolvaptan. Urine aquaporin-2 has recently been demonstrated as a promising predictor of response to tolvaptan. We here validated aquaporin-2-guided tolvaptan therapy in patients with decompensated heart failure. Long-term efficacy of tolvaptan treatment in the responders defined by aquaporin-2 needs to be validated in the future prospective study.