scholarly journals High Constitutive Signaling of the Ghrelin Receptor—Identification of a Potent Inverse Agonist

2003 ◽  
Vol 17 (11) ◽  
pp. 2201-2210 ◽  
Author(s):  
Birgitte Holst ◽  
Adam Cygankiewicz ◽  
Tine Halkjær Jensen ◽  
Michael Ankersen ◽  
Thue W. Schwartz
Keyword(s):  
Inositol Phosphate ◽  
Inverse Agonist ◽  
Negative Control ◽  
Appetite Control ◽  
Ghrelin Receptor ◽  
Physiological Importance ◽  
Gh Secretion ◽  
293 Cells ◽  
Treatment Of Obesity ◽  
Motilin Receptor

Abstract Ghrelin is a GH-releasing peptide that also has an important role as an orexigenic hormone-stimulating food intake. By measuring inositol phosphate turnover or by using a reporter assay for transcriptional activity controlled by cAMP-responsive elements, the ghrelin receptor showed strong, ligand-independent signaling in transfected COS-7 or human embryonic kidney 293 cells. Ghrelin and a number of the known nonpeptide GH secretagogues acted as agonists stimulating inositol phosphate turnover further. In contrast, the low potency ghrelin antagonist, [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P was surprisingly found to be a high potency (EC50 = 5.2 nm) full inverse agonist as it decreased the constitutive signaling of the ghrelin receptor down to that observed in untransfected cells. The homologous motilin receptor functioned as a negative control as it did not display any sign of constitutive activity; however, upon agonist stimulation the motilin receptor signaled as strongly as the unstimulated ghrelin receptor. It is concluded that the ghrelin receptor is highly constitutively active and that this activity could be of physiological importance in its role as a regulator of both GH secretion and appetite control. It is suggested that inverse agonists for the ghrelin receptor could be particularly interesting for the treatment of obesity.

scholarly journals Ghrelin Receptor (GHS-R1a) and Its Constitutive Activity in Somatotroph Adenomas: A New Co-targeting Therapy Using GHS-R1a Inverse Agonists and Somatostatin Analogs

2014 ◽  
Vol 99 (12) ◽  
pp. E2463-E2471 ◽  
Author(s):  
Yves Mear ◽  
Marie-Pierre Blanchard ◽  
Céline Defilles ◽  
Thierry Brue ◽  
Dominique Figarella-Branger ◽  
...  
Keyword(s):  
Somatostatin Receptor ◽  
Somatostatin Analogs ◽  
Inverse Agonist ◽  
Receptor Subtype ◽  
Dependent Manner ◽  
Constitutive Activity ◽  
Targeting Therapy ◽  
Ghrelin Receptor ◽  
Gh Secretion

Context: The ghrelin receptor GHS-R1a is highly expressed in human somatotroph adenomas and exhibits unusually high basal signaling activity. In humans, the suppression of this constitutive activity by mutation induces a short stature. Objective: Using a GHS-R1a inverse agonist, modified substance P (MSP), we explored the role of GHS-R1a constitutive activity in GH hypersecretion from somatotroph adenomas and as a putative therapeutic target. Design: The effects of MSP were assessed on GH secretion from 19 human somatotroph tumors in vitro. Moreover, these effects were compared with those of octreotide (somatostatin receptor subtype 2 [sst2] agonist) and with the combination of both drugs. Expression and localization of GHS-R1a and sst2 were studied. Results: For all tumors, MSP inhibited GH secretion in a dose-dependent manner from 13 to 64%. Moreover, MSP enhanced octreotide-induced GH inhibition. For five tumors, the effects of combined MSP plus octreotide treatment were significantly higher than the sum of effects of each drug alone. MSP increased the membrane localization of GHS-R1a and of microdomains colocalizing sst2-GHS-R1a, highlighting the cooperation between the two drugs. Conclusions: The GHS-R1a inverse agonist could open new therapeutic options for acromegalic patients, particularly patients partially sensitive to octreotide whose GH secretion is not completely controlled by the sst2 agonist.

Differential effects of passive immunization with somatostatin antiserum on adenohypophysial hormone secretions in starved rats

1986 ◽  
Vol 109 (2) ◽  
pp. 169-174 ◽  
Author(s):  
J. N. Hugues ◽  
A. Enjalbert ◽  
E. Moyse ◽  
C. Shu ◽  
M. J. Voirol ◽  
...  
Keyword(s):  
Binding Capacity ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Passive Immunization ◽  
Negative Control ◽  
Prolactin Secretion ◽  
Male Rats ◽  
Minimal Effective Dose ◽  
Gh Secretion

ABSTRACT The role of somatostatin (SRIF) on adenohypophysial hormone secretion in starved rats was reassessed by passive immunization. Because of the absence of pulsatile GH secretion in starved rats, the effects of the injection of SRIF antiserum on GH levels can be clearly demonstrated. To determine whether starvation modifies the sensitivity of the adenohypophysis to SRIF, we measured 125I-labelled iodo-N-Tyr-SRIF binding. There was no difference in the dissociation constant (Kd) nor in the maximal binding capacity (Bmax) in fed (n = 15) and starved (n = 15) animals (Kd = 0·38 ± 0·09 (s.e.m.) and 0·45 ± 0·09 nmol; Bmax = 204 ± 39 and 205 ± 30 fmol/mg protein respectively). Administration of SRIF antiserum resulted in a dose-dependent increase in plasma concentrations of GH, TSH and prolactin. The minimal effective dose of SRIF antiserum was 50 μl for GH, 100 μl for TSH and 200 μl for prolactin. Our results show that: (1) starvation does not modify adenohypophysial SRIF-binding sites, (2) in starved male rats endogenous SRIF exerts a negative control on prolactin secretion in vivo and (3) sensitivity to endogenous SRIF seems to be different for each hypophysial cell type. J. Endocr. (1986) 109, 169–174

scholarly journals Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

2019 ◽  
Vol 47 (8) ◽  
pp. 874-882 ◽  
Author(s):  
Sravani Adusumalli ◽  
Rohitash Jamwal ◽  
R. Scott Obach ◽  
Tim F. Ryder ◽  
Lorenzo Leggio ◽  
...  
Keyword(s):  
Inverse Agonist ◽  
The Novel ◽  
Ghrelin Receptor ◽  
Receptor Inverse Agonist

scholarly journals Alteration of intracellular histamine H2 receptor cycling precedes antagonist-induced upregulation

2005 ◽  
Vol 289 (5) ◽  
pp. G880-G889 ◽  
Author(s):  
Satoshi Osawa ◽  
Masayoshi Kajimura ◽  
Seiji Yamamoto ◽  
Mutsuhiro Ikuma ◽  
Chihiro Mochizuki ◽  
...  
Keyword(s):  
Fluorescent Protein ◽  
Inverse Agonist ◽  
Recycling Endosome ◽  
Histamine H2 Receptor ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
293 Cells ◽  
Gfp Fluorescence ◽  
Term Administration ◽  
Green Fluorescent

Long-term administration of a histamine H2 receptor (H2R) antagonist (inverse agonist) induces upregulation of H2R in parietal cells, which may be relevant to the rebound hypersecretion of gastric acid that occurs after withdrawal of treatment. The mechanisms underlying this effect are unknown. We hypothesized that the H2R upregulation could be related to receptor trafficking and used H2R-green fluorescent protein (H2R-GFP) to test the hypothesis. Human H2R-GFP was generated and functionally expressed in HEK-293 cells. Binding of the H2R antagonist [3H]tiotidine was performed to quantify H2R expression, and H2R-GFP was imaged in living cells by confocal and evanescent wave microscopy. The binding affinity of [3H]tiotidine was not significantly different between H2R-GFP- and wild-type H2R-expressing HEK-293 cells, both of which had constitutive activity of adenylate cyclase. Visualization of H2R-GFP revealed that the agonist-induced H2R internalization and the antagonist-induced recycling of the internalized H2R from the recycling endosome within 2 h. Long exposure to the antagonist increased GFP fluorescence in the plasma membrane and also induced upregulation of H2R-GFP estimated by the binding assay, whereas long exposure to the agonist enhanced degradative trafficking of H2R-GFP. We examined whether the upregulation reflected an increase in receptor synthesis. Treatment with antagonist did not augment H2R mRNA, and subsequent inhibition of protein synthesis by cycloheximide had no effect on H2R upregulation. These findings suggested that upon exposure to an antagonist (inverse agonist), the equilibrium between receptor endocytosis and recycling is altered before H2R upregulation, probably via suppressing H2R degradation.

Nocturnal ghrelin pulsatility and response to growth hormone secretagogues in healthy men

2004 ◽  
Vol 287 (3) ◽  
pp. E506-E512 ◽  
Author(s):  
Polyxeni Koutkia ◽  
Bridget Canavan ◽  
Jeff Breu ◽  
Michael L. Johnson ◽  
Steven K. Grinspoon
Keyword(s):  
Growth Hormone ◽  
Repeated Measures ◽  
Hormone Secretion ◽  
Approximate Entropy ◽  
Growth Hormone Secretagogues ◽  
Physiological Regulation ◽  
Physiological Importance ◽  
Gh Secretion ◽  
Maximal Peak ◽  
The Mean

The physiological importance of endogenous ghrelin in the regulation of growth hormone (GH) secretion is still unknown. To investigate the regulation of ghrelin secretion and pulsatility, we performed overnight ghrelin and GH sampling every 20 min for 12 h in eight healthy male subjects [age 37 ± 5 (SD) years old, body mass index 27.2 ± 2.9 kg/m2]. Simultaneous GH and ghrelin levels were assessed to determine the relatedness and synchronicity between these two hormones in the fasted state during the overnight period of maximal endogenous GH secretion. Pulsatility analyses were performed to determine simultaneous hormonal dynamics and investigate the relationship between GH and ghrelin by use of cross-approximate entropy (X-ApEn) analyses. Subjects demonstrated 3.0 ± 2.1 ghrelin pulses/12 h and 3.3 ± 0.9 GH pulses/12 h. The mean normalized ghrelin entropy (ApEn) was 0.93 ± 0.09, indicating regularity in ghrelin hormone secretion. The mean normalized X-ApEn was significant between ghrelin and GH (0.89 ± 0.12), demonstrating regularity in cosecretion. In addition, we investigated the ghrelin response to standard GH secretagogues [GH-releasing hormone (GHRH) alone and combined GHRH-arginine] in separate testing sequences separated by 1 wk. Our data demonstrate that, in contrast to GHRH alone, which had little effect on ghrelin, combined GHRH and arginine significantly stimulated ghrelin with a maximal peak at 120 min, representing a change of 66 ± 14 pg/ml ( P = 0.001 by repeated-measures ANOVA and P = 0.02 for GHRH vs. combined GHRH-arginine by MANOVA). We demonstrate relatedness between ghrelin and GH pulsatility, suggesting either that ghrelin participates in the pulsatile regulation of GH or that the two hormones are simultaneously coregulated, e.g., by somatostatin or other stimuli. Furthermore, the differential effects of GHRH alone vs. GHRH-arginine suggest that inhibition of somatostatin tone may increase ghrelin. These data provide further evidence of the physiological regulation of ghrelin in relationship to GH.

scholarly journals Recombinant Adenovirus Expressing Vesicular Stomatitis Virus G Proteins induce both humoral and cell-medicated immune responses in Mice and Goats

2020 ◽  
Author(s):  
Xiaojuan Xue ◽  
Zhaorong Yu ◽  
Hongyan Jin ◽  
Lin Liang ◽  
Jiayang Li ◽  
...  
Keyword(s):  
Immune Responses ◽  
G Proteins ◽  
Vesicular Stomatitis Virus ◽  
Immune Cell ◽  
Recombinant Adenovirus ◽  
Negative Control ◽  
Direct Immunofluorescence ◽  
Post Inoculation ◽  
293 Cells ◽  
Vesicular Stomatitis

Abstract Background: With a human type 5 replication-defective adenovirus expression vector, we constructed the three recombinant adenoviruses (rAd) and expressed the Vesicular Stomatitis Virus (VSV) Indiana serotype glycoprotein (VSV-IN-G), VSV New Jersey serotype glycoprotein (VSV-NJ-G), and the G fusion protein [two serotypes G (VSV-IN-G-NJ-G)]. Three rAds were named rAd-IN, rAd-NJ, and rAd-IN-NJ. The three rAds were inoculated into AAV-293 cells, and the AAV-293 cells were serially propagated to 20 generations until the virus titers were stable, then TCID50 was determined. In direct immunofluorescence and western blot were used for detecting the expression of the target proteins and lymphocyte proliferation test was used for immune cell numbers. Results: The results showed that G proteins we expressed with good reactogenicity. The rAds were used to subcutaneously inoculate mice three times with 2-week intervals, and goats two times with 3-week intervals, respectively. On 0, 2, 4, and 6 weeks of post-inoculation for the mice and 0, 3, 6, 9, and 12 weeks for goats, their sera were collected and NT antibodies were determined. The results showed that the rAds could induce the production of VSV antibodies in the mice, and VSV NT antibodies in the goats. The antibody levels were 1:16 to 1: 32 in mice, and 1:32 to 1: 64 in the goats. The rAds induced strong immune lymphocyte proliferations in mice and goats, which was significantly higher than those of the negative control groups. Conclusion: The three rAds expressed VSV-G proteins at high levels, and induced humoral and cellular immune responses in both mice and goats, which laid a foundation for further studies of the recombinant adenovirus vaccines expressing VSV glycoprotein.

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