Effects of the beta3-adrenoceptor (Adrb3) agonist SR58611A (amibegron) on serotonergic and noradrenergic transmission in the rodent: relevance to its antidepressant/anxiolytic-like profile.

SR58611A is a selective beta(3)-adrenoceptor (Adrb3) agonist which has demonstrated antidepressant and anxiolytic properties in rodents. The present study confirmed the detection of Adrb3 mRNA transcript in rodent brain sub-regions and evaluated the effect of SR58611A on serotonergic and noradrenergic transmission in rats and mice in an attempt to elucidate the mechanism(s) underlying these properties. SR58611A (3 and 10 mg/kg, p.o.) increased the synthesis of 5-HT and tryptophan (Trp) levels in several rodent brain areas (cortex, hippocampus, hypothalamus, striatum). Moreover, SR58611A (10 mg/kg, p.o.) increased the release of 5-HT assessed by in vivo microdialysis in rat prefrontal cortex. Systemic (3 mg/kg, i.v.) or chronic administration of SR58611A (10 mg/kg, p.o.), in contrast to fluoxetine (15 mg/kg, p.o.), did not modify the activity of serotonergic neurons in the rat dorsal raphe nucleus. The increase in 5-HT synthesis induced by SR58611A was not observed in Adrb3s knockout mice, suggesting a selective involvement of Adrb3s in this effect. SR58611A (3 and 10 mg/kg, p.o.) did not modify norepinephrine synthesis and metabolism but increased its release in rat brain. Repeated administration of SR58611A (10 mg/kg, p.o.) did not modify basal norepinephrine release in rat prefrontal cortex whereas it prevented its tail-pinch stress-induced enhancement similarly to reboxetine (15 mg/kg, p.o.). Finally SR58611A increased the firing rate of noradrenergic neurons in the rat locus coeruleus following systemic (3 mg/kg, i.v.) or local (0.01 and 1 microM) but not chronic (10 mg/kg, p.o.) administration. These results suggest that the anxiolytic- and antidepressant-like activities of SR58611A involve an increase of brain serotonergic and noradrenergic neurotransmissions, triggered by activation of Adrb3s.

Biochemical and pharmacological properties of SR 49059, a new, potent, nonpeptide antagonist of rat and human vasopressin V1a receptors.

SR 49059, a new potent and selective orally active, nonpeptide vasopressin (AVP) antagonist has been characterized in several in vitro and in vivo models. SR 49059 showed high affinity for V1a receptors from rat liver (Ki = 1.6 +/- 0.2) and human platelets, adrenals, and myometrium (Ki ranging from 1.1 to 6.3 nM). The previously described nonpeptide V1 antagonist, OPC-21268, was almost inactive in human tissues at concentrations up to 100 microM. SR 49059 exhibited much lower affinity (two orders of magnitude or more) for AVP V2 (bovine and human), V1b (human), and oxytocin (rat and human) receptors and had no measurable affinity for a great number of other receptors. In vitro, AVP-induced contraction of rat caudal artery was competitively antagonized by SR 49059 (pA2 = 9.42). Furthermore, SR 49059 inhibited AVP-induced human platelet aggregation with an IC50 value of 3.7 +/- 0.4 nM, while OPC-21268 was inactive up to 20 microM. In vivo, SR 49059 inhibited the pressor response to exogenous AVP in pithed rats (intravenous) and in conscious normotensive rats (intravenous and per os) with a long duration of action (> 8 h at 10 mg/kg p.o). In all the biological assays used, SR 49059 was devoid of any intrinsic agonistic activity. Thus, SR 49059 is the most potent and selective nonpeptide AVP V1a antagonist described so far, with marked affinity, selectivity, and efficacy toward both animal and human receptors. With this original profile, SR 49059 constitutes a powerful tool for exploring the therapeutical usefulness of a selective V1a antagonist.

Characterization of SR 121463A, a highly potent and selective, orally active vasopressin V2 receptor antagonist.

SR 121463A, a potent and selective, orally active, nonpeptide vasopressin V2 receptor antagonist, has been characterized in several in vitro and in vivo models. This compound displayed highly competitive and selective affinity for V2 receptors in rat, bovine and human kidney (0.6 < or = Ki [nM] < or = 4.1). In this latter preparation, SR 121463A potently antagonized arginine vasopressin (AVP)-stimulated adenylyl cyclase activity (Ki = 0.26+/-0.04 nM) without any intrinsic agonistic effect. In autoradiographic experiments performed in rat kidney sections, SR 121463A displaced [3H]AVP labeling especially in the medullo-papillary region and confirmed that it is a suitable tool for mapping V2 receptors. In comparison, the nonpeptide V2 antagonist, OPC-31260, showed much lower affinity for animal and human renal V2 receptors and lower efficacy to inhibit vasopressin-stimulated adenylyl cyclase (Ki in the 10 nanomolar range). Moreover, OPC-31260 exhibited a poor V2 selectivity profile and can be considered as a V2/V1a ligand. In normally hydrated conscious rats, SR 121463A induced powerful aquaresis after intravenous (0.003-0.3 mg/kg) or oral (0.03-10 mg/kg) administration. The effect was dose-dependent and lasted about 6 hours at the dose of 3 mg/kg p.o. OPC-31260 had a similar aquaretic profile but with markedly lower oral efficacy. The action of SR 121463A was purely aquaretic with no changes in urine Na+ and K+ excretions unlike that of known diuretic agents such as furosemide or hydrochlorothiazide. In addition, no antidiuretic properties have been detected with SR 121463A in vasopressin-deficient Brattleboro rats. Thus, SR 121463A is the most potent and selective, orally active V2 antagonist yet described and could be a powerful tool for exploring V2 receptors and the therapeutical usefulness of V2 blocker aquaretic agents in water-retaining diseases.

The immunosuppressant SR 31747 blocks cell proliferation by inhibiting a steroid isomerase in Saccharomyces cerevisiae.

SR 31747 is a novel immunosuppressant agent that arrests cell proliferation in the yeast Saccharomyces cerevisiae, SR 31747-treated cells accumulate the same aberrant sterols as those found in a mutant impaired in delta 8- delta 7-sterol isomerase. Sterol isomerase activity is also inhibited by SR 31747 in in vitro assays. Overexpression of the sterol isomerase-encoding gene, ERG2, confers enhanced SR resistance. Cells growing anaerobically on ergosterol-containing medium are not sensitive to SR. Disruption of the sterol isomerase-encoding gene is lethal in cells growing in the absence of exogenous ergosterol, except in SR-resistant mutants lacking either the SUR4 or the FEN1 gene product. The results suggest that sterol isomerase is the target of SR 31747 and that both the SUR4 and FEN1 gene products are required to mediate the proliferation arrest induced by ergosterol depletion.

Molecular cloning, expression and function of the murine CB2 peripheral cannabinoid receptor.

We have cloned the peripheral cannabinoid receptor, mCB2, from a mouse splenocyte cDNA library. The 3.7 kb sequence contains an open reading frame encoding a protein of 347 residues sharing 82% overall identity with the only other known peripheral receptor, human CB2 (hCB2) and shorter than hCB2 by 13 amino acids at the carboxyl terminus. Binding experiments with membranes from COS-3 cells transiently expressing mCB2 showed that the synthetic cannabinoid WIN 55212-2 had a 6-fold lower affinity for mCB2 than for hCB2, whereas both receptors showed similar affinities for the agonists CP 55,940, delta(9)-THC and anandamide and almost no affinity for the central receptor- (CB1) specific antagonist SR 141716A. Both hCB2 and mCB2 mediate agonist-stimulated inhibition of forskolin-induced cAMP production in CHO cell lines permanently expressing the receptors. SR 141716A failed to antagonize this activity in either cell line, confirming its specificity for CB1.

High-level production of a human membrane protein in yeast: the peripheral-type benzodiazepine receptor.

The human peripheral-type benzodiazepine receptor (PBR) has been produced in Saccharomyces cerevisiae where it retains its pharmacological properties [Riond et al., Eur. J. Pharmacol. 208 (1991) 307-312]. As the rate of production was low, we analysed the mRNA level, the effect of variation of the 5' sequence and the production in mitochondria. Translation rather than transcription or targeting was found to be the main limiting factor. We were able to produce a chimeric PBR, with an N-terminal extension, to a very high level in the yeast mitochondrial membrane.

Characterization of a peripheral-type benzodiazepine-binding site in the mitochondria of Chinese hamster ovary cells.

The isoquinoline carboxamide derivative [3H]PK11195, a ligand for the peripheral-type benzodiazepine (BZD) receptor, binds to Chinese hamster ovary (CHO) cell mitochondria in a specific and saturable manner. Scatchard analysis showed the presence of a single-binding site with an apparent dissociation constant (Kd) of 12.0 +/- 1.0 nM and a maximal binding capacity of 23.0 +/- 2.0 pmol/mg protein. The pharmacological characterization of this CHO BZD-binding site, based on the displacement of [3H]PK11195 by several drugs of known binding specificity, indicated that it is of the peripheral-type. The photoaffinity probe [3H]PK14105, a nitrophenyl derivative of [3H]PK11195, specifically labeled a 17 kDa CHO mitochondrial protein. This 17 kDa protein was purified from digitonin-solubilized mitochondria by gel-filtration chromatography and two reverse-phase HPLC steps. The purified material migrated as a single band on silver stained or autoradiographed SDS-polyacrylamide gels, and had an amino acid composition corresponding to a 17 kDa protein rich in Leu, Val, Ala, Gly, and Pro. Analysis of the amino-terminal sequence of the purified 17 kDa protein revealed a blocked amino-terminus.

The rat beta 3-adrenergic receptor gene contains an intron.

We report that the rat beta 3-adrenergic receptor (beta 3-AR) gene has an intron. The intron starts with an in-frame stop codon with the result that unspliced transcripts will encode a C-terminal truncated protein. The reported protein sequences of mouse and human beta 3-AR were both deduced from genomic DNA sequences. Given the heterogeneity at the C-termini of the otherwise highly similar rat, mouse and human sequences, we discuss the intriguing possibility that the beta 3-AR gene of the latter two species also contain an intron near the extremity of the open reading frame. A beta-adrenergic receptor (beta-AR) cDNA we have cloned from rat colonic tissue which has a sequence essentially identical to that previously reported for the rat adipose beta 3-AR cDNA [(1991) J. Chem. 266, 24053], encodes the spliced version of the beta 3-AR.

The NK1 receptor is involved in the neurokinin-induced shape change of rabbit platelets.

Substance P and selective neurokinin receptor agonists have been tested for their ability to induce shape change in rabbit platelets. Substance P and the NK1 receptor agonist Ac [Arg6,Sar9,Met(O2)11]-substance P (6-11) induced shape change (EC50 = 3 and 6 nM, respectively), whereas the selective NK2 agonist [Nle10]-Neurokinin A (4-10) and the selective NK3 agonist [MePhe7]-Neurokinin B did not show any effect. Moreover, the specific NK1 receptor antagonist CP-96,345 selectively and dose-dependently counteracted the effect of substance P or of the NK1 receptor agonist (IC50 = 2 and 0.8 nM, respectively), whereas the selective NK2 receptor antagonist, SR 48968, had no effect. Unlike for serotonin or low doses of ADP, epinephrine did not allow substance P or the NK1 receptor agonist to become a proaggregating substance. These data therefore show that the NK1 receptor is solely involved in the neurokinin-induced shape change of rabbit platelets.

Cannabinoids enhance human B-cell growth at low nanomolar concentrations.

This study examined the effect of cannabinoid ligands on human tonsillar B-cells activated either through cross-linking of surface immunoglobulins or ligation of the CD40 antigen. The two synthetic cannabinoids, CP55,940 and WIN55212-2, as well as delta 9-tetrahydrocannabinol (THC), the psychoactive component of marijuana, caused a dose-dependent increase of B-cell proliferation and displayed EC50 at low nanomolar concentrations. This cannabinoid-induced enhancing activity was inhibited by pertussis toxin which suggested a G-protein-coupled receptor process. In addition, the absence of antagonistic effect of SR141716A, a specific CB1 receptor antagonist, together with the demonstration that human B-cells displayed large amount of CB2 receptor mRNAs, led us to assume that the growth enhancing activity observed on B-cells at very low concentrations of cannabinoids could be mediated through the CB2 receptor.

Molecular basis for the different binding properties of benzodiazepines to human and bovine peripheral-type benzodiazepine receptors.

The 18 kDa peripheral benzodiazepine receptor (PBR) can be labelled by benzodiazepines, such as Ro5-4864, and isoquinoline carboxamides such as PK11195. These two compounds are reversible competitive inhibitors of each other. However, while the binding affinity of Ro5-4864 varies enormously across species, PK11195 always displays high affinity, suggesting that their binding domains are overlapping but not identical. We report here that recombinant human and bovine PBR produced in yeast, a microorganism devoid of endogenous PBR, can be labelled with [3H]PK11195, but only the human receptor can be labelled with [3H]Ro5-4864. Furthermore, we identified, through the binding analysis of human-bovine chimaeric receptors, a region near the C-terminal end of the PBR, with only five non-conserved amino acids between human and bovine sequences, as responsible for the difference in high affinity binding of Ro5-4864 to the two receptors.

Stimulation of peripheral cannabinoid receptor CB2 induces MCP-1 and IL-8 gene expression in human promyelocytic cell line HL60.

Using the recently developed methodology of nucleic acid microarrays spotted with specific cDNAs probes belonging to different gene families, we showed for the first time that nanomolar concentrations of the cannabinoid ligand CP-55940 upregulated the expression of two different members of the chemokine gene family: the alpha-chemokine interleukin-8 (IL-8) and the beta-chemokine monocyte chemotactic protein-1 (MCP-1), in the promyelocytic cell line HL60 transfected with peripheral cannabinoid receptors (CB2). These genomic modulations observed on large-scale cDNA arrays were first confirmed by Northern blot studies. Furthermore, ELISA evaluations in culture supernatants indicated that the cannabinoid-induced activation of these two chemokine genes was followed by enhanced expression and secretion of the corresponding proteins. These upregulations initially observed in transfected HL60 cells overexpressing CB2 receptors, also occurred in normal non-transfected HL60 cells. The enhancement of IL-8 and MCP-1 gene transcription and protein production was shown to be pertussis toxin sensitive attesting that this phenomenon was a Gi protein-coupled receptor-mediated process as expected for cannabinoid receptors. More specifically, the abolition of the cannabinoid-induced effect by the specific CB2 antagonist SR 144528 indicated a strict peripheral cannabinoid-mediated process. Altogether, our data highlight a possible new function of peripheral cannabinoid receptors in the modulation of immune and inflammatory responses.

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 Y(1) receptor transcripts with Y(4) and Y(5) and absence of Y(2) 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 [(125)I]peptide YY (PYY) and [(125)I](Leu(31), Pro(34))PYY. These sites exhibited a typical Y(1) 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 [(35)S]GTPgammaS 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 Y(1) ligands enhanced adipocyte leptin secretion, an effect totally prevented by SR120819A. Thus, highly expressed in human adipocytes, the Y(1) receptor sustains the strong antilipolytic effect of NPY and exerts a positive action on leptin secretion.

Effect of substance P on cytokine production by human astrocytic cells and blood mononuclear cells: characterization of novel tachykinin receptor antagonists.

Substance P (SP) has been reported to induce inflammatory cytokine production in human neuroglial cells and peripheral lymphoid cells as well. In order to evaluate the potency of novel non-peptide antagonists of the tachykinin receptors as inhibitors of SP-induced cytokines, we used the astrocytoma cell line U373MG and blood mononuclear cells as models of central and peripheral SP-target cells, respectively. In the first part of this study, we showed that SR 140333, an NK1 tachykinin receptor antagonist, was able to inhibit strongly the SP-induced production of interleukin (IL)-6 and IL-8 in the astrocytoma cell line. The antagonistic activity of SR 140333 toward SP-induced cytokine production was specific and could not be attributed to a general anti-cytokine effect, since cytokine release induced by another inflammatory protein such as IL-1beta was not blocked by this compound. In addition, NK2 and NK3 agonist neuropeptides were at least 1000-fold less effective than SP, while SR 48968 and SR 142801 which are selective NK2 and NK3 receptor antagonists, respectively, displayed a 2.5-3 orders of magnitude lower inhibitory potency than SR 140333. All these data indicated that SR 140333 blocked SP-induced cytokine production in U373MG astrocytic cells via a specific NK1 receptor-mediated process. Since SP has also been described to trigger peripheral blood mononuclear cells (PBMNC) or monocytes to release inflammatory cytokines, we attempted, in the second part of this study, to evaluate the potential antagonistic effect of our compounds on these cells. Experiments on human PBMNC from different donors were carried out to determine first their pattern of cytokine production upon SP stimulation. Surprisingly, we noticed that SP at concentrations ranging from 0.1 to 1000 nM was unable to stimulate the release of any inflammatory cytokine tested. This raises the question of the specificity of the reported in vitro effects of SP on cytokine production by human peripheral immune cells.

Characterization and localization of leptin receptors in the rat kidney.

Characterization and localization of leptin binding sites were investigated in rat kidneys using [125I]leptin as a ligand. [125I]Leptin specific binding was found in high amounts in rat renomedullary membranes. This binding was specific, saturable, time-dependent (K(obs) = 0.055 +/- 0.008 min(-1)) and the dissociation of receptor-bound ligand was slowly reversible (K(-1) = 0.048 +/- 0.013 min(-1)). From saturation experiments, a single class of high-affinity binding sites for leptin was identified with an apparent K(d) of 0.57 +/- 0.14 nM and a B(max) of 45 +/- 10 fmol/mg protein. [125I]Leptin binding was inhibited in a dose-dependent manner by cold leptin and was highly selective since not displaceable by a number of other hormones or peptides. Autoradiographic experiments performed on adult rat kidney sections showed the intense presence of [125I]leptin receptors only in specific areas of the renal inner medulla and also consistent labeling associated with vascular structures in the corticomedullary region. The study of the postnatal developmental expression of leptin receptors in the kidney showed very low expression during the early postnatal period (8-21 days). Full expression of leptin sites was achieved at about 30 days and remained stable throughout adulthood (60 days and upwards). Moreover, in vivo administration of leptin (0.5 mg/kg i.p.) induced a significant and rapid diuretic effect in normally hydrated conscious rats. Thus, these data constitute the first characterization and mapping of [125I]leptin specific binding sites in the rat kidney and raise the possibility of a renal control by leptin.

Cloning and expression of a complementary DNA encoding a high affinity human neurotensin receptor.

A human neurotensin receptor (hNTR) cDNA was cloned from the colonic adenocarcinoma cell line HT29. The cloned cDNA encodes a putative peptide of 418 amino acids with 7 transmembrane domains. The amino acid sequence of the hNTR is 84% identical to the rat NTR [Neuron, 4 (1990) 847-854]. Transfection of this cDNA into COS cells results in the expression of receptors with pharmacological properties similar to those found with HT29 cells. Northern blot analysis using the hNTR cDNA probe indicated a single transcript of 4 kb in the brain, the small intestine and blood mononuclear cells.

Molecular cloning of a levocabastine-sensitive neurotensin binding site.

A search for sequences homologous to the neurotensin receptor cDNA in a rat hypothalamic library has identified a novel neurotensin receptor (NTR-2). The 1539 bp cDNA encodes a 416 amino acid protein and shows highest homology to the previously cloned neurotensin receptor (NTR-1) (64% homology and 43% identity). Binding and pharmacological studies demonstrate that NTR-2 expressed in COS cells recognizes neurotensin (NT) with high affinity as well as several other agonists and antagonists. However, a fundamental difference was found; unlike NTR-1, NTR-2 recognizes, with high affinity, levocabastine, a histamine H1 receptor antagonist previously shown to compete with NT for low-affinity binding sites in brain.

Primary structure and functional expression of mouse pituitary and human brain corticotrophin releasing factor receptors.

Corticotrophin-releasing factor (CRF) is the principal hypothalamic factor governing the pituitary-adrenal axis, but the wide extra-pituitary distribution of CRF and its receptors suggest a major role for this neuropeptide in the integration of the overall physiological and behavioral responses of an organism to stress. We have cloned a CRF receptor complementary DNA (cDNA) by expression in COS-7 cells of a cDNA library from the AtT20 mouse pituitary tumour cell line. The cloned mouse cDNA was then as a probe to isolate a human CRF receptor cDNA from a human brain cDNA library. The mouse and human cDNAs both encode 415 amino acid proteins that are 97% identical, containing seven putative transmembrane domains characteristic of G protein-coupled receptors. The CRF receptor shows homology with the receptors for growth hormone-releasing factor, vasoactive intestinal peptide, secretin, parathyroid hormone, and calcitonin. COS-7 cells transfected with the mouse CRF receptor cDNA bind radiolabelled ovine CRF with high affinity and respond specifically to CRF by accumulation of intracellular cAMP. A 2.7 kb mRNA coding for the CRF receptor could be detected in AtT20 cells and human cortex tissue. PCR analysis also detected the receptor transcript in human pituitary, brainstem, and testis.

The ability of PK 8165, a quinoline derivative, to reduce responses to a stressful situation in a double-blind study in man.

A double-blind and cross-over study was carried out in order to explore the effects of PK 8165 (a quinoline derivative) on the heart rate, respiratory rate and motor reflex responses produced by an experimental model of stress in 8 healthy volunteers. The stress was induced by repetitive sequences of anticipation of pain (stressful stimulus: S) spaced by resting periods (R). In a control session, the cumulative effects of S resulted, in all subjects, in a progressive increase in heart and respiratory rates; 5 subjects showed a cumulative facilitation in the H reflex (motor reflex response) while the 3 others exhibited a cumulative depression in this motor parameter as a function of repetition of S during the session. The three doses (50, 100, 150 mg) of PK 8165 produced a very significant dose-dependent reduction in these responses during both stressful periods and resting sequences. Furthermore, the baseline values of respiratory and especially heart rate were also significantly reduced in a dose-dependent fashion by PK 8165. In contrast, the treatment with placebo did not significantly modify these parameters, compared to control values. The functional implications of these data are discussed in terms of stress-induced activation of some CNS structures and of the possible mechanisms of the "anti-stress" effect of PK 8165.

Involvement of potentially distinct neurotensin receptors in neurotensin-induced stimulation of striatal [3H]dopamine release evoked by KCl versus electrical depolarization.

We intended to determine whether the effect of neurotensin (NT) on K+ and electrically evoked [3H]dopamine (DA) release from rat and guinea-pig striatal slices involved different mechanisms and/or receptors. In the two species, NT and three NT agonists were found to exhibit different relative potencies to enhance K+- and electrically-evoked [3H]DA release. NT(1-13) increased [3H]DA release with EC50 values in the nanomolar range and Emax values in the range of 100% of control. NT(8-13) and Eisai hexapeptide were both as active as NT(1-13) under K+ depolarization, but did not exceed 40% of the NT(1-13) effect under electrical depolarization. In rats, when [3H]DA release was stimulated with two successive K+ depolarizations, in the presence of NT(1-13), the NT effect during the second exposure to K+ was drastically decreased, suggesting that the NT receptor was desensitized. The desensitization process was essentially observed on Emax values, EC50 values being weakly affected. Similar results were obtained in guinea pig. In contrast, with two electrical depolarizations or with two different depolarizations (K+ followed by electrical), the NT effect during the second depolarization was not significantly affected. Concerning NT antagonists, SR 48692 antagonized with IC50 values in the nanomolar range the NT(1-13) stimulated K+-evoked [3H]DA release but did not affect, up to 10(-6) M, the NT(1-13) enhancement of electrically stimulated [3H]DA release. On the contrary, SR 142948A antagonized the NT(1-13) effect on K+- and electrically-evoked [3H]DA release. In conclusion, these results suggest the possible existence of potentially distinct neurotensin receptors differentially involved in the control exerted by NT on DA release under KCl vs electrical depolarization.