Characterization of a functional V1B vasopressin receptor in the male rat kidney: evidence for cross talk between V1B and V2 receptor signaling pathways.

Although vasopressin V1B receptor (V1BR) mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using the selective V1B agonist d[Leu4, Lys8]VP, either fluorescent or radioactive, we showed that V1BR is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V1BR were very low compared with the V2 receptor (V2R). On the microdissected IMCD, d[Leu4, Lys8]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca2+ concentration increase mobilization with an EC50 value in the nanomolar range. This effect involved both intracellular Ca2+ mobilization and extracellular Ca2+ influx. The selective V1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca2+ concentration but also cAMP, suggesting a cooperation between V1BR and V2R in IMCD cells expressing both receptors. This cooperation arises from a cross talk between second messenger cascade involving PKC rather than receptor heterodimerization, as supported by potentiation of arginine vasopressin-stimulated cAMP production in human embryonic kidney-293 cells coexpressing the two receptor isoforms and negative results obtained by bioluminescence resonance energy transfer experiments. In vivo, only acute administration of high doses of V1B agonist triggered significant diuretic effects, in contrast with injection of selective V2 agonist. This study brings new data on the localization and signaling pathways of V1BR in the kidney, highlights a cross talk between V1BR and V2R in the IMCD, and suggests that V1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V2R activation.NEW & NOTEWORTHY Although V1BR mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using original pharmaceutical tools, this study brings new data on the localization and signaling pathways of V1BR, highlights a cross talk between V1BR and V2 receptor (V2R) in the inner medullary collecting duct, and suggests that V1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V2R activation.

Proinflammatory role of vasopressin through V1b receptors in hapten-induced experimental colitis in rodents: implication in IBD.

Vasopressin and its receptors modulate several gut functions, but their role in intestinal inflammation is unknown. Our aims were to determine 1) the localization of V1b receptors in human and rodent colon, 2) the role of vasopressin and V1b receptors in experimental colitis using two approaches: V1b⁻(/)⁻ mice and a selective V1b receptor antagonist, SSR149415, and 3) the mechanisms involved. V1b receptors were localized in normal and inflamed colon from humans and rats. Experimental colitis was induced in rats and mice and some groups were treated before or after colitis induction with oral SSR149415 (3-30 mg/kg). Other groups of mice were submitted to dehydration to increase vasopressin plasma levels, prior to colitis induction. Body weight, damage scores, MPO, and TNF-α tissue levels were determined. Finally, colonic segments of wild-type (WT) and V1b⁻(/)⁻ mice were mounted in Ussing chambers and paracellular permeability in response to vasopressin was studied. V1b receptors were expressed in enterocytes and ganglia cells of the enteric nervous system of human and rat intestine. Expression levels were independent from inflammatory status. Colitis was less severe in rodents treated by either preventive or curative SSR149415 and in V1b⁻(/)⁻ mice. 2,4,6-Trinitrobenzene sulfonic acid induced a strong mortality in dehydrated animals that was reversed by preventive SSR149415 or mast cell stabilizer. Vasopressin significantly increased paracellular permeability in WT, but not in V1b⁻(/)⁻ mice. Preincubation of colon tissues with SSR149415 abolished the vasopressin effect. Similarly, vasopressin had no effect in colonic preparations from WT mice pretreated with mast cell stabilizers. Vasopressin, through V1b receptor interaction, has proinflammatory properties linked to mast cell activation and downstream alterations of the colonic epithelial barrier. These findings underline the potential interest of V1b receptor blockers in gut inflammatory diseases.

Pharmacological and physiological characterization of d[Leu4, Lys8]vasopressin, the first V1b-selective agonist for rat vasopressin/oxytocin receptors.

Recently, we synthesized and characterized the first selective V(1b) vasopressin (VP)/oxytocin receptor agonist, d[Cha(4)]arginine vasopressin. However, this agonist was only selective for the human receptors. We thus decided to design a selective V(1b) agonist for the rodent species. We started from previous observations showing that modifying [deamino(1),Arg(8)]VP in positions 4 and 8 altered the rat VP/oxytocin receptor selectivity. We synthesized a series of 13 [deamino(1),Arg(8)]VP analogs modified in positions 4 and 8. Among them, one seemed very promising, d[Leu(4), Lys(8)]VP. In this paper, we describe its pharmacological and physiological properties. This analog exhibited a nanomolar affinity for the rat, human, and mouse V(1b) VP receptors and a strong V(1b) selectivity for the rat species. On AtT20 cells stably transfected with the rat V(1b) receptor, d[Leu(4), Lys(8)]VP behaved as a full agonist on both phospholipase C and MAPK assays. Additional experiments revealed its ability to induce the internalization of enhanced green fluorescent protein-tagged human and mouse V(1b) receptors as expected for a full agonist. Additional physiological experiments were performed to further confirm the selectivity of this peptide. Its antidiuretic, vasopressor, and in vitro oxytocic activities were weak compared with those of VP. In contrast, used at low doses, its efficiency to stimulate adrenocorticotropin or insulin release from mouse pituitary or perfused rat pancreas, respectively, was similar to that obtained with VP. In conclusion, d[Leu(4), Lys(8)]VP is the first selective agonist available for the rat V(1b) VP receptor. It will allow a better understanding of V(1b) receptor-mediated effects in rodents.

Comparative pharmacology of bovine, human and rat vasopressin receptor isoforms.

In this study, we characterized the bovine vasopressin V(1a), V(1b), V(2) receptor isoforms and compared their pharmacological properties to those of corresponding rat and human vasopressin receptor subtypes. Specific binding sites of high affinity for vasopressin were found in all bovine tissues tested (kidney, liver and pituitary). Using a large series of recent peptidic and non-peptidic selective vasopressin agonists or antagonists, we demonstrated the presence of vasopressin V(2), V(1a) or V(1b) receptors in the kidney, liver and pituitary bovine tissues, respectively. This extensive characterization of bovine vasopressin receptor isoforms validates the pharmacological vasopressin receptor classification earlier established for the rat and human species. As expected, the bovine vasopressin receptors look much more like human receptors than rat ones. Interestingly, among the three vasopressin receptor isoforms studied, the vasopressin V(1b) receptor subtype is the best conserved for the three species studied.

Vasopressin does not mediate hypersensitivity of the hypothalamic pituitary adrenal axis during chronic stress.

The hypothesis that vasopressin (VP) becomes the main mediator of pituitary corticotroph responsiveness during chronic hypothalamic pituitary adrenal (HPA) axis activation was tested by examining the effect of pharmacologic VP receptor blockade on the adrenocorticotropic hormone (ACTH) and corticosterone responses of 14-day repeatedly restrained rats. In spite of the increased vasopressinergic activity, repeatedly restrained rats showed lower ACTH and corticosterone responses to 10 min white noise compared with handled controls. These responses were unchanged by injection of the nonpeptide-selective V1b receptor antagonist SSR149415 i.v., 1 h before noise application. In contrast to noise stress, plasma ACTH responses to i.p. hypertonic saline injection were enhanced in the repeatedly restrained rats compared with handled controls, but responses were also unaffected by SSR149415 administered orally, daily 1 h before restraint. Since SSR149415 effectiveness was low, we used minipump infusion of the peptide V1 receptor antagonist, dGly[Phaa1,D-tyr(et), Lys, Arg]VP (V1-Ant) for 14 days, which effectively blocked ACTH responses to exogenous VP. Chronic V1-Ant infusion reduced plasma ACTH responses to i.p. hypertonic saline in handled controls but not in repeatedly restrained rats. These data suggest that the increased vasopressinergic activity characteristic of chronic stress plays roles other than mediating the hypersensitivity of the HPA axis to a novel stress.

Biological characterization of rodent and human vasopressin V1b receptors using SSR-149415, a nonpeptide V1b receptor ligand.

[(3)H]SSR-149415 is the first tritiated nonpeptide vasopressin V(1b) receptor (V(1b)R) antagonist ligand. It was used for studying rodent (mouse, rat, hamster) and human V(1b)R from native or recombinant origin. Moreover, a close comparison between the human and the mouse V(1b)R was performed using SSR-149415/[(3)H]SSR-149415 in binding and functional studies in vitro. [(3)H]SSR-149415 binding was time-dependent, reversible, and saturable. Scatchard plot analysis gave a single class of high-affinity binding sites with apparent equilibrium dissociation constant (K(d)) approximately 1 nM and maximum binding density (B(max)) values from 7,000 to 300,000 sites/cell according to the cell line. In competition experiments, [(3)H]SSR-149415 binding was stereospecific and dose-dependently displaced by reference peptide and nonpeptide arginine vasopressin (AVP)/OT ligands following a V(1b) rank order of affinity: SSR-149415 = AVP > dCha > dPen > dPal > dDavp > SSR-126768A > SR-49059 > SSR-149424 > OT > SR-121463B. Species differences between human, rat, mouse, and hamster V(1b)R were observed. Autoradiography studies with [(3)H]SSR-149415 on rat and human pituitary showed intense specific labeling confined to corticotroph cells and absence of labeling in the other tissues examined. SSR-149415 potently and stereospecifically antagonized the AVP-induced inositol phosphate production and intracellular Ca(2+) increase (EC(50) from 1.83 to 3.05 nM) in recombinant cell lines expressing either the mouse or the human V(1b)R. AVP (10(-7) M) exposure of AtT20 cells expressing mouse or human EGFP-tagged V(1b)R induced their rapid internalization. Preincubation with 10(-6) M SSR-149415 counteracted the internalization process. Moreover, recycling of internalized receptors was observed upon 10(-6) M SSR-149415 treatment. Thus SSR-149415/[(3)H]SSR-149415 are unique tools for studying animal and human V(1b)R.

PKD1 haploinsufficiency causes a syndrome of inappropriate antidiuresis in mice.

Mutations in PKD1 are associated with autosomal dominant polycystic kidney disease. Studies in mouse models suggest that the vasopressin (AVP) V2 receptor (V2R) pathway is involved in renal cyst progression, but potential changes before cystogenesis are unknown. This study used a noncystic mouse model to investigate the effect of Pkd1 haploinsufficiency on water handling and AVP signaling in the collecting duct (CD). In comparison with wild-type littermates, Pkd1(+/-) mice showed inappropriate antidiuresis with higher urine osmolality and lower plasma osmolality at baseline, despite similar renal function and water intake. The Pkd1(+/-) mice had a decreased aquaretic response to both a water load and a selective V2R antagonist, despite similar V2R distribution and affinity. They showed an inappropriate expression of AVP in brain, irrespective of the hypo-osmolality. The cAMP levels in kidney and urine were unchanged, as were the mRNA levels of aquaporin-2 (AQP2), V2R, and cAMP-dependent mediators in kidney. However, the (Ser256) phosphorylated AQP2 was upregulated in Pkd1(+/-) kidneys, with AQP2 recruitment to the apical plasma membrane of CD principal cells. The basal intracellular Ca(2+) concentration was significantly lower in isolated Pkd1(+/-) CD, with downregulated phosphorylated extracellular signal-regulated kinase 1/2 and decreased RhoA activity. Thus, in absence of cystic changes, reduced Pkd1 gene dosage is associated with a syndrome of inappropriate antidiuresis (positive water balance) reflecting decreased intracellular Ca(2+) concentration, decreased activity of RhoA, recruitment of AQP2 in the CD, and inappropriate expression of AVP in the brain. These data give new insights in the potential roles of polycystin-1 in the AVP and Ca(2+) signaling and the trafficking of AQP2 in the CD.

An overview of SSR149415, a selective nonpeptide vasopressin V(1b) receptor antagonist for the treatment of stress-related disorders.

Vasopressin (AVP) and corticotropin-releasing factor (CRF) are key mediators in the organism's neuro-adaptive response to stress. Through pituitary and central vasopressin V(1b) receptors, AVP participates in the control of the hypothalamic-pituitary-adrenal axis (HPA) and is involved in various emotional processes. SSR149415 is the first selective, orally active vasopressin V(1b) receptor antagonist yet described. It is a competitive antagonist with nanomolar affinity for animal and human V(1b) receptors and displays a highly selective profile with regard to a large number of receptors or enzymes. In vitro, SSR149415 potently antagonizes functional cellular events associated with V(1b) receptor activation by AVP, such as intracellular Ca(2+) increase or proliferation in various cell systems. Pharmacological studies, performed by measuring ACTH secretion induced by various stimulants such as hormones (AVP or AVP + CRF) or physical stress (restraint or forced swimming stress and dehydration) in conscious rats or mice, confirm the antagonist profile of SSR149415 and its efficacy in normalizing ACTH secretion in vivo. SSR149415 is active by the oral route, at doses from 3 mg/kg, it potentiates CRF effect and displays a long-lasting oral effect in the different models. At 10 mg/kg p.o. its duration of action is longer than 4 h. This molecule also decreases anxiety and exerts marked antidepressant-like activity in several predictive animal models. The anxiolytic effects of SSR149415 have been demonstrated in various Generalized Anxiety Disorders (GAD) models (four-plate, punished drinking, elevated plus-maze, light dark, mouse defense test battery, fear-potentiated startle and social interaction tests). It is as effective as the benzodiazepine diazepam in the acute stress exposure test. SSR149415 has similar efficacy to the reference antidepressant drug, fluoxetine, in acute (forced-swimming) and chronic (chronic mild stress and subordination stress) situations in rodents. SSR149415 also reduces offensive aggression in the resident-intruder model in mice and hamsters. Depending on the model, the minimal effective doses are in the range of 1-10 mg/kg i.p. or 3-10 mg/kg p.o. SSR149415 is devoid of adverse effects on motor activity, sedation, memory or cognitive functions and produces no tachyphylaxis when administered repeatedly. It is well-tolerated in animals and humans and exhibits an adequate ADME profile. Thus, SSR149415 is a new dual anxiolytic/antidepressant compound, which appears to be free of the known side effects of classical anxiolytic/antidepressant drugs. Clinical trials are in progress, they will hopefully demonstrate its therapeutical potential for treating stress-related disorders.

Pancreatic vasopressin V1b receptors: characterization in In-R1-G9 cells and localization in human pancreas.

Vasopressin (AVP) receptors present in In-R1-G9 cells, a hamster glucagon-secreting alpha-pancreatic cell line, were characterized using SSR-149415, a selective nonpeptide V1b receptor antagonist, and reference AVP compounds. Binding experiments, using [3H]AVP as a ligand, identified a single population of high-affinity binding sites. SSR-149415 competitively inhibited this binding and exhibited nanomolar and stereospecific affinity for these sites. The affinity of various AVP/oxytocin ligands confirmed a V1b binding profile. In functional studies, AVP was a potent stimulant in inducing intracellular Ca2+ increase, glucagon secretion, and cell proliferation. These effects were fully antagonized by SSR-149415 with a nanomolar potency, whereas its diasteroisomer as well as two selective V1a and V2 receptor antagonists were much less potent. Additionally, the order of potency of AVP agonists and antagonists was in agreement with V1b-mediated effects. By RT-PCR, we confirmed the presence of V1b receptor mRNA in both In-R1-G9 cells and in human pancreas. The distribution pattern of V1b receptors investigated in human pancreas by immunohistochemistry showed strong labeling in islets of Langerhans, and colocalization studies indicated that this receptor was expressed in alpha-glucagon, beta-insulin, and somatostatin pancreatic cells. Thus, in In-R1-G9 cells, AVP mediates intracellular Ca2+ increase, glucagon secretion, and cell proliferation by activating V1b receptors, and these effects are potently antagonized by SSR-149415. Moreover, the presence of V1b receptors also found in human Langerhans islets could suggest hormonal control of AVP in human pancreas.

Functional and pharmacological characterization of the first specific agonist and antagonist for the V1b receptor in mammals.

By activating three distinct vasopressin receptor isoforms called V1a-R, V1b-R (V3-R) and V2-R, vasopressin (VP) mediates a wide number of biological effects in mammals and may be involved in several pathological states. Up to now only specific V1a and V2 receptor agonists and antagonists have been successfully designed. The role of the V1b-R still remains partially unknown, due to the lack of selective V1b-R ligands and orally-active molecules, which are crucial tools for investigating the central and peripheral functions or pathological disorders associated with this receptor. In this review, we report the biological and pharmacological properties of the first two specific V1b-R ligands: d[Cha4] AVP, a high affinity V1b-R agonist and SSR149415, a potent orally-active V1b-R antagonist with good selectivity with respect to other VP/OT receptor isoforms and able to control ACTH secretion in vitro and in vivo. Indeed, these molecules constitute invaluable tools for exploring the central and peripheral roles of VP mediated via V1b receptors. Interestingly, SSR149415 displays potent anxiolytic and antidepressant-like activities, indicating that this new class of drugs has a promising therapeutical potential in the treatment of stress-related disorders, anxiety and depression.

Anxiolytic- and antidepressant-like effects of the non-peptide vasopressin V1b receptor antagonist, SSR149415, suggest an innovative approach for the treatment of stress-related disorders.

The limbic localization of the arginine vasopressin V(1b) receptor has prompted speculation as to a potential role of this receptor in the control of emotional processes. To investigate this possibility, we have studied the behavioral effects of SSR149415, the first selective and orally active non-peptide antagonist of vasopressin V(1b) receptors, in a variety of classical (punished drinking, elevated plus-maze, and light/dark tests) and atypical (fear/anxiety defense test battery and social defeat-induced anxiety) rodent models of anxiety, and in two models of depression [forced swimming and chronic mild stress (CMS)]. When tested in classical tests of anxiety, SSR149415 produced anxiolytic-like activity at doses that ranged from 1 to 30 mg/kg (i.p. or p.o.), but the magnitude of these effects was overall less than that of the benzodiazepine anxiolytic diazepam, which was used as a positive control. In contrast, SSR149415 produced clear-cut anxiolytic-like activity in models involving traumatic stress exposure, such as the social defeat paradigm and the defense test battery (1-30 mg/kg, p.o.). In the forced swimming test, SSR149415 (10-30 mg/kg, p.o.) produced antidepressant-like effects in both normal and hypophysectomized rats. Moreover, in the CMS model in mice, repeated administration of SSR149415 (10 and 30 mg/kg, i.p.) for 39 days improved the degradation of the physical state, anxiety, despair, and the loss of coping behavior produced by stress. These findings point to a role for vasopressin in the modulation of emotional processes via the V(1b) receptor, and suggest that its blockade may represent a novel avenue for the treatment of affective disorders.

Characterization of (2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), a selective and orally active vasopressin V1b receptor antagonist.

(2S,4R)-1-[5-Chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), the first selective, nonpeptide vasopressin V1b receptor antagonist yet described, has been characterized in vitro and in vivo. SSR149415 showed competitive nanomolar affinity for animal and human V1b receptors and exhibited much lower affinity for rat and human V1a, V2, and oxytocin receptors. Moreover, this compound did not interact with a large number of other receptors, enzymes, or ion channels. In vitro, SSR149415 behaved as a full antagonist and potently inhibited arginine vasopressin (AVP)-induced Ca2+ increase in Chinese hamster ovary cells expressing rat or human V1b receptors. The in vivo activity of SSR149415 has been studied in several models of elevated corticotropin secretion in conscious rats. SSR149415 inhibited exogenous AVP-induced increase in plasma corticotropin, from 3 mg/kg i.p. and 10 mg/kg p.o. upwards. Similarly, this compound antagonized AVP-potentiated corticotropin release provoked by exogenous corticoliberin at 3 mg/kg p.o. The effect lasted for more than 4 h at 10 mg/kg p.o. showing a long-lasting oral effect. SSR149415 (10 mg/kg p.o.) also blocked corticotropin secretion induced by endogenous AVP increase subsequent to body water loss. Moreover, 10 mg/kg i.p SSR149415 inhibited plasma corticotropin elevation after restraint-stress in rats by 50%. In the four-plate test, a mouse model of anxiety, SSR149415 (3 mg/kg p.o. upwards) displayed anxiolytic-like activity after acute and 7-day repeated administrations. Thus, SSR149415 is a potent, selective, and orally active V1b receptor antagonist. It represents a unique tool for exploring the functional role of V1b receptors and deserves to be clinically investigated in the field of stress and anxiety.

SSR126768A (4-chloro-3-[(3R)-(+)-5-chloro-1-(2,4-dimethoxybenzyl)-3-methyl-2-oxo-2,3-dihydro-1H-indol-3-yl]-N-ethyl-N-(3-pyridylmethyl)-benzamide, hydrochloride): a new selective and orally active oxytocin receptor antagonist for the prevention of preterm labor.

4-chloro-3-[(3R)-(+)-5-chloro-1-(2,4-dimethoxybenzyl)-3-methyl-2-oxo-2,3-dihydro-1H-indol-3-yl]-N-ethyl-N-(3-pyridylmethyl)benzamide, hydrochloride (SSR126768A), a new potent and selective, orally active oxytocin (OT) receptor antagonist was characterized in several biochemical and pharmacological models. In binding studies, SSR126768A showed nanomolar affinity for rat and human recombinant and native OT receptors (K(i) = 0.44 nM) and exhibited much lower affinity for V(1a), V(1b), and V(2) receptors. In addition, it did not interact with a large number of other receptors, enzymes, and ion channels (1 microM). In autoradiographic experiments performed on at-term human pregnant uterus sections, SSR126768A dose dependently displaced [I(125)]d(CH(2))(5)[Tyr(Me)(2), Thr(4), Orn(8) (125)I-Tyr-NH(2)(9)]VT in situ labeling to OT receptors highly expressed in these tissues. In functional studies, SSR126768A behaved as a full antagonist and potently antagonized OT-induced intracellular Ca(2+) increase (K(i) = 0.50 nM) and prostaglandin release (K(i) = 0.45 nM) in human uterine smooth muscle cells. In rat isolated myometrium, OT-induced uterine contractions were competitively antagonized by SSR126768A (pA(2) = 8.47). Similarly, in human pregnant myometrial strips, SSR126768A inhibited the contractile uterine response to OT. In conscious telemetrated rats, oral administration of SSR126768A (1-10 mg/kg) produced a competitive inhibition of the dose response to OT on uterine contractions up to 24 h at 3 mg/kg p.o.; no tachyphylaxis was observed after 4-day repeated treatment. Finally, SSR126768A (30 mg/kg p.o.) significantly delayed parturition in pregnant rats in labor similar to ritodrine (10 mg/kg p.o.). Thus, SSR126768A is a potent, highly selective, orally active OT receptor antagonist with a long duration of action. This molecule could find therapeutic application as a tocolytic agent for acute and chronic oral management of preterm labor.