Claudine Serradeil-Le Gal

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 V1b 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 V1b 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 V1b receptor, and suggest that its blockade may represent a novel avenue for the treatment of affective disorders.

Characterization and localization of leptin receptors in the rat kidney

© 1997 Federation of European Biochemical Societies.

Non-Peptide Vasopressin V1b Receptor Antagonists as Potential Drugs for the Treatment of Stress-Related Disorders

Since vasopressin has been shown to be critical for adaptation of the hypothalamo-pituitary-adrenal axis during stress through its ability to potentiate the stimulatory effect of CRF, it has been hypothesized that this peptide may provide a good opportunity for pharmacological treatment of stress-related disorders. The availability of the first orally active non-peptide V(1b) receptor antagonist, SSR149415, opened a new era for examining the role of vasopressin in animal models of anxiety and depression. In rats, SSR149415 blocked several endocrine (i.e. ACTH release), neurochemical (i.e. noradrenaline release) and autonomic (i.e. hyperthermia) responses following various stress exposures. Moreover, the drug was able to attenuate some but not all stress-related behaviors in rodents. While the antidepressant-like activity of the compound was comparable to that of reference antidepressants, the overall profile displayed in anxiety tests was different from that of classical anxiolytics, such as benzodiazepines. These latter were highly effective and reliably produced robust effects in most anxiety tests, while SSR149415 showed clear-cut effects only in particularly stressful situations. Experiments with mice or hamsters indicated that V(1b) receptor blockade is associated with reduced aggressiveness, suggesting that SSR149415 could prove useful for treating aggressive behavior. It is important to note that SSR149415 is devoid of adverse effects on motor functions or cognitive processes, and it did not produce tolerance to its anxiolytic- or antidepressant-like activity. Altogether, these findings suggest that V(1b) receptor antagonists represent a promising alternative to agents currently used for the treatment of depression and some forms of anxiety disorders.

Characterization of NPY receptors controlling lipolysis and leptin secretion in human adipocytes

In order to characterize neuropeptide Y (NPY) receptors present in human adipocytes, we used selective ligands together with specific molecular probes able to recognize the different NPY receptor subtypes. RT‐PCR experiments revealed the presence of Y1 receptor transcripts with Y4 and Y5 and absence of Y2 signals. Binding studies, using selective radioiodinated ligands, detected a high number (B max=497±124 fmol/mg protein) of a high affinity binding site only with [125I]peptide YY (PYY) and [125I](Leu31,Pro34)PYY. These sites exhibited a typical Y1 profile as indicated by the rank order of affinity of NPY analogs and the high affinity of two selective NPY receptor antagonists, SR120819A and BIBP3226. In [35S]GTPγS binding experiments, PYY activation was totally inhibited by SR120819A and BIBP3226. Both compounds antagonized, with similar efficiency, the antilipolytic effect exerted by NPY in isolated adipocytes. Finally, PYY and Y1 ligands enhanced adipocyte leptin secretion, an effect totally prevented by SR120819A. Thus, highly expressed in human adipocytes, the Y1 receptor sustains the strong antilipolytic effect of NPY and exerts a positive action on leptin secretion.

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.

Binding of the Non-Peptide Vasopressin V1a Receptor Antagonist SR-49059 in the Rat Brain: An in vitro and in vivo Autoradiographic Study

A potent non-peptide vasopressin (AVP) antagonist, SR-49059, displaying high stability and selective affinity for the V1a AVP receptor subtype, has recently been described. The objective of this study was to assess the binding properties and the penetrability of this compound in the rat brain. Both in vitro and in vivo binding autoradiography experiments were performed. In all studies, the liver was used as a reference V1a tissue. In vitro labelling of rat brain sections with [3H]SR-49059 was similar to that previously detected with [3H]AVP, which confirms that the majority of central AVP binding sites are V1a sites similar to peripheral V1a receptors. As expected, intense specific labelling occurred mainly in the lateral septum, the fundus striatum, the hypothalamic stigmoid nucleus and the area postrema-nucleus of the solitary tract complex. In vivo binding autoradiography showed that [3H]SR-49059 injected intravenously did not enter the brain parenchyma. Specific labelling was however clearly detectable in brain regions with permeable hematoencephalic barrier, the choroid plexus and other circumventricular organs expressing V1a receptors, namely the subfornical organ, the pineal gland and the area postrema. The specificity of [3H]SR-49059 binding in the latter structures was confirmed by the fact that labelling was prevented by pretreatment of animals with high doses of nonradioactive SR-49059. In conclusion, our study shows that [3H]SR-49059 is a suitable probe to investigate V1a receptors in the rat brain. We also demonstrate that although this compound is not able to enter the brain tissue from the peripheral circulation, it does bind specifically to regions devoid of blood-brain barrier and known to be involved in autonomic regulations.

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.

Chapter 4.2 – Nonpeptide vasopressin V1b receptor antagonists

Abstract Arginine vasopressin (AVP) is critical for adaptation of the hypothalamo–pituitary–adrenal axis during stress through its ability to potentiate the stimulatory effect of CRF. This observation, taken together with the identification of AVP receptors (e.g. V 1b ) in limbic structures has led to the idea that this peptide may provide a good opportunity for pharmacological treatment of stress-related disorders. The availability of an orally active nonpeptide V 1b receptor antagonist has allowed to verify this hypothesis. Studies in animals have shown that the V 1b receptor antagonist, SSR149415, is able to attenuate some but not all stress-related behaviors in rodents. While the antidepressant-like effects of the compound was comparable to that of reference antidepressants, the overall profile displayed in anxiety tests was different from that of classical anxiolytics, such as benzodiazepines. While the latter were active in a wide range of anxiety models, the AVP antagonist showed clear-cut effects only in particularly stressful situations. Moreover, SSR 149415 blocked several endocrine (i.e. ACTH release), neurochemical (i.e. noradrenaline release) and autonomic (i.e. heart rate) responses following acute stress exposure in rats. It is noteworthy that SSR149415 was devoid of central effects not related to emotionality. Altogether, these findings suggest that blockade of central V 1b receptors may represent a new therapeutic strategy for the treatment of depression and some forms of anxiety disorders.