Ghrelin is a gut-brain peptide hormone that plays an important role in the control of energy metabolism. In the mouse, the expression of its receptor, growth hormone secretagogue receptor (GHSR), was reported to be highest in two brain regions, the arcuate nucleus (ARC) in the hypothalamus and non-preganglionic Edinger-Westphal nucleus (npEW) in the midbrain. The npEW is also the most dominant site of urocortin 1 (Ucn1) expression in the mammalian brain and the npEW-Ucn1 neurons play an important role in stress adaptation response. Despite the importance of ghrelin for regulating food intake and body weight, mice lacking ghrelin or GHSR show no, or only a modest metabolic phenotype. Because GHSR mRNA is abundantly present in the stress-sensitive npEW, we hypothesized that ghrelin is not only involved in metabolism control but also in the stress response. To test this we studied the ghrelin-KO mice, under basal non-stressed and acute stressed conditions. Under basal conditions, KO mice have higher activation of npEW-Ucn1 neurons as demonstrated by dual label Ucn-1 and Fos immunohistochemistry. After restraint stress both wild-type (WT) and KO mice revealed an increased activation of the npEW nucleus, but we found that stress recruited Ucn1-ir neurons only in WT, but not in KO mice. We also determined Ucn1 mRNA expression in stressed and non-stressed conditions in KO and WT mice by in situ hybridization and found a strong up-regulation of Ucn1 mRNA in KO than in WT mice. Moreover, KO but not WT mice revealed stress-induced Ucn1 mRNA expression. Taken together, our data provide evidence for ghrelin actions in stress response. We propose that Ucn1 neurons in the npEW are instrumental in ghrelin´s action on the animal´s stress adaptation response.
L. Xu et al., C137 Deletion of ghrelin alters the response of Edinger-Westphal nucleus to restraint stress in the mouse. Poster session presented at IBRO 2011. 8th International Brain Research Organization World Congress of Neuroscience; 2011 July 14-18; Florence, Italy.
We provide the first evidence for the existence in human plasma of peptides derived from the 66 carboxyl-terminal amino acids of pro-ghrelin (C-ghrelin). C-ghrelin immunoreactivity in plasma was higher than ghrelin, and did not significantly correlate with body mass index in normal health. In patients with myocardial infarction, plasma levels of both ghrelin and C-ghrelin were significantly decreased ( approximately 30%, P<0.05), whereas in patients with heart failure, C-ghrelin levels were significantly elevated ( approximately 32%, P<0.05) compared with controls. HPLC coupled with RIA showed circulating C-ghrelin to be primarily of low molecular weight (M(r) approximately 3500), but in chronic heart failure, a higher molecular weight form (M(r) approximately 7500) is also present. This is the first evidence for potential circulating hormones derived from the carboxyl terminus of pro-ghrelin and for their modulation in cardiovascular diseases.
Experimental studies have suggested that ghrelin plays a role in glucose homeostasis and in the regulation of blood pressure (BP). We therefore assessed the hypothesis that a low ghrelin concentration may be a risk factor for type 2 diabetes and hypertension. We also characterized the effect of the ghrelin Arg51Gln and Leu72Met mutations on ghrelin concentrations in the population-based hypertensive (n = 519) and control (n = 526) cohorts of our OPERA (Oulu Project Elucidating Risk of Atherosclerosis) study. The fasting plasma ghrelin concentrations of 1,040 subjects were analyzed using the radioimmunoassay method. Insulin sensitivity was assessed using the quantitative insulin sensitivity check index (QUICKI). Ghrelin concentrations were negatively associated with fasting insulin (P < 0.001), systolic (P = 0.026) and diastolic BP (P = 0.018), and the prevalence of type 2 diabetes (P = 0.015) and insulin resistance (P < 0.001) in the multivariate models. In the control cohort, low ghrelin was associated with hypertension (BP >140/90 mmHg) (P = 0.031). The subjects with the ghrelin 51Gln allele had lower ghrelin concentrations than the Arg51Arg homozygotes (P = 0.001). We conclude that low ghrelin is independently associated with type 2 diabetes, insulin concentration, insulin resistance, and elevated BP. Therefore, it might have some role in the etiology of type 2 diabetes and the regulation of BP. The ghrelin Arg51Gln mutation is associated with low plasma ghrelin concentrations.
A human study investigating the biological activities of non-acylated ghrelin revealed antagonizing properties of this peptide on the hyperglycemic effects of acylated (or active) ghrelin. More specifically, bolus injections (i.v.) of this inactive form of ghrelin caused a significant reversal of the active ghrelin-induced reduction in insulin levels and ghrelin-induced increase in plasma glucose levels. This indicates a novel mechanism for the control of glucose levels in the blood and hence may lead to potential therapeutic applications of the non-acylated form of ghrelin in the treatment of type II diabetes and insulin resistance-related conditions.
Broglio F, Prodam F, Benso A , et al.,Endo 2003, PHiladelphia, June 2003, Abstract #553
Ghrelin, a growth hormone-releasing hormone produced by gastroenteropancreatic endocrine cells, hypothalamus, and pituitary, was recently identified in medullary thyroid carcinomas and derived cell lines. However, no data exist on its expression in either normal or neoplastic thyroid follicular cells. We analyzed ghrelin expression by immunohistochemistry, in situ hybridization, and reverse transcriptase-polymerase chain reaction in 15 fetal, 4 infant, and 10 adult thyroids, and in 54 tumors of follicular origin. We also analyzed the effects of ghrelin on cell proliferation in N-PAP and ARO thyroid carcinoma cell lines. Ghrelin-binding sites were investigated using reverse transcriptase-polymerase chain reaction to detect its growth hormone secretagogue receptor (GHS-R) mRNA and an in situ-binding localization procedure. Strong ghrelin immunoreactivity was found in fetal but not in infant or adult thyroids. Ghrelin protein and mRNA were present, in variable amounts, in benign and malignant tumors. Normal thyroids, thyroid tumors, and cell lines showed ghrelin binding sites by binding localization, in the absence of the specific GHS receptor mRNA (with the exception of one normal thyroid). Moreover, ghrelin induced dose-dependent inhibition of growth in cell lines. In conclusion, ghrelin is expressed in fetal but not in adult thyroid, and is re-expressed in tumors; the presence of ghrelin receptors other than GHS-R in normal and neoplastic adult thyroid is suggested; ghrelin inhibits cell proliferation of thyroid carcinoma cell lines in vitro.
The novel hormone ghrelin is a potent orexigen that may counterbalance leptin. Ghrelin is the only secreted molecule requiring post-translational acylation with octanoic acid to ensure bioactivity. Ghrelin, predominantly derived from the stomach, may target neuroendocrine networks within the central nervous system (CNS) to regulate energy homeostasis. This would require ghrelin to cross the blood-brain barrier (BBB). In mice, we examined whether ghrelin crosses the BBB and whether its lipophilic side chain is involved in this process. We found that saturable systems transported human ghrelin from brain-to-blood and from blood-to-brain. Mouse ghrelin, differing from human ghrelin by two amino acids, was a substrate for the brain-to-blood but not for the blood-to-brain transporter and so entered the brain to a far lesser degree. des-Octanoyl ghrelin entered the brain by nonsaturable transmembrane diffusion and was sequestered once within the CNS. In summary, we show that ghrelin transport across the BBB is a complex, highly regulated bidirectional process. The direction and extent of passage are determined by the primary structure of ghrelin, defining a new role for the unique post-translational octanoylation.
Ghrelin is an acyl-peptide gastric hormone acting on the pituitary and hypothalamus to stimulate growth hormone (GH) release, adiposity, and appetite. Ghrelin endocrine activities are entirely dependent on its acylation and are mediated by GH secretagogue (GHS) receptor (GHSR)-1a, a G protein–coupled receptor mostly expressed in the pituitary and hypothalamus, previously identified as the receptor for a group of synthetic molecules featuring GH secretagogue (GHS) activity. Des-acyl ghrelin, which is far more abundant than ghrelin, does not bind GHSR-1a, is devoid of any endocrine activity, and its function is currently unknown. Ghrelin, which is expressed in heart, albeit at a much lower level than in the stomach, also exerts a cardio protective effect through an unknown mechanism, independent of GH release. Here we show that both ghrelin and des-acyl ghrelin inhibit apoptosis of primary adult and H9c2 cardiomyocytes and endothelial cells in vitro through activation of extracellular signal–regulated kinase-1/2 and Akt serine kinases. In addition, ghrelin and des-acyl ghrelin recognize common high affinity binding sites on H9c2 cardiomyocytes, which do not express GHSR-1a. Finally, both MK-0677 and hexarelin, a nonpeptidyl and a peptidyl synthetic GHS, respectively, recognize the common ghrelin and des-acyl ghrelin binding sites, inhibit cell death, and activate MAPK and Akt.
These findings provide the first evidence that, independent of its acylation, ghrelin gene product may act as a survival factor directly on the cardiovascular system through binding to a novel, yet to be identified receptor, which is distinct from GHSR-1a.
Baldanzi G, Filigheddu N, Cutrupi S, et al. Ghrelin and des-acyl ghrelin inhibit cell death in cardiomyocytes and endothelial cells through ERK1/2 and PI 3-kinase/AKT. J Cell Biol. 2002;159(6):1029-37
Circulating Ghrelin Levels Are Decreased in Human Obesity
|Fasting plasma Ghrelin (Human)||514+/-63 pg/ml n=24||Otto B, et al. Eur J Endocrinol 2001 Nov;145(5):669-73|
|Fasting plasma Ghrelin (Human)||1057+/-95 pg/ml (anorectic patients||Otto B, et al. Eur J Endocrinol 2001 Nov;145(5):669-73|
|Ghrelin (Human)||307 +/- 164 [Prader-Willi syndrome (PWS)]||DelParigi A., et al. J Clin Endocrinol Metab 2002 Dec;87(12):5461-4|
|Ghrelin (Human)||109 +/- 24 fmol/ml||DelParigi A., et al. J Clin Endocrinol Metab 2002 Dec;87(12):5461-4|
|Fasting serum ghrelin levels (Human)||270 +/- 102 pmol/liter||Haqq AM, et al. J Clin Endocrinol Metab 2003 Jan;88(1):174-8|
|Fasting serum ghrelin levels (Human)||429 +/- 374 pmol/liter [Prader-Willi Syndrome (PWS)]||Haqq AM, et al. J Clin Endocrinol Metab 2003 Jan;88(1):174-8|
|Fasting serum ghrelin levels (Human)||139 +/- 70 pmol/liter (Obese group)||Haqq AM, et al. J Clin Endocrinol Metab 2003 Jan;88(1):174-8|
|Fasting plasma ghrelin||87+/-28 pmol/liter (Pima Indians)||Tschop M, et al. Diabetes 2001 Apr;50(4):707-9|
|Fasting plasma ghrelin||129+/-34 fmol/ml (Caucasians)||Tschop M, et al. Diabetes 2001 Apr;50(4):707-9|
|fasting healthy lean children (NC)||426.0; 183.0-618.0 pg/ml||Bellone S., et al. J Endocrinol Invest 2002 May;25(5):RC13-5|
|fasting obese children (OBC)||229.5; 162.5-339.5 pg/ml||Bellone S., et al. J Endocrinol Invest 2002 May;25(5):RC13-5|
|Fastin healthy lean adults (NA)||380.5; 257.7-551.7 pg/ml||Bellone S., et al. J Endocrinol Invest 2002 May;25(5):RC13-5|
|Time of Use*||Week 0||Week 2||Week 4|
|1 x||5.75pg (57.5pg/ml)||12.3pg (123pg/ml)||7.65pg (76.5pg/ml)|
Stability of Ghrelin (Human) RIA Kit(at least 3 weeks in liquid form)
Stability of Ghrelin (Human) RIA Kit (at least 4 weeks in dry form)
*Kits used in Week 0 were used within 2 days of manufacture. All kits used in Week 2 and 4 were stored as dry power (not reconstituted) at 4oC.
Phoenix strongly recommends using the RIA kit as soon as possible. Always store the unused kit as dry power at 4oC if not used immediately. Never store reconstituted kit components as they are unstable. Use of stored reconstituted kit components to perform RIA may yield poor and unacceptable results. Phoenix's Ghrelin (Human) RIA Kit detects "total" Ghrelin, including Ser3- octanoyl and Ser3-des-octanoyl Ghrelins.
|031-31||Ghrelin (Rat, Mouse)||100 µg||$102|
|EK-031-30||Ghrelin (Human) - EIA Kit, extraction-free||96 wells||$458|
|031-49||Ghrelin (1-11) (Rat, Mouse, Porcine)||100 µg||$194|
|031-30||Ghrelin (Human)||100 µg||$102|
|RK-031-30||Ghrelin (Human) - RIA Kit||125 tubes||$406|
|031-52||Ghrelin (Porcine)||100 µg||$194|
|EK-031-31||Ghrelin (Rat, Mouse) - EIA Kit, extraction-free||96 wells||$458|
|EK-031-50||Ghrelin (Canine) - EIA Kit, extraction-free||96 wells||$458|
|H-031-31||Ghrelin (Rat, Mouse) - Antibody||100 µl||$459|
|031-33||Ghrelin (Rat, Mouse)||100 µg||$153|
|T-031-31||Ghrelin (Rat, Mouse) - I-125 Labeled||10 µCi||$723|
|031-32||Ghrelin (Human)||100 µg||$133|
|031-42||Ghrelin (1-5) amide (Human, Rat, Mouse, Bovine, Canine)||200 µg||$28|
|EK-031-30CE||Ghrelin (Human) - EIA Kit, extraction-free, CE Mark Certified||96 wells||$478|
|RK-031-52||Ghrelin (Porcine) - RIA Kit||125 tubes||$671|
|032-33||GMA-Ghrelin (1-9) amide (Rat, Mouse)||200 µg||$153|
|032-34||GMA-Ghrelin amide (Rat, Mouse)||200 µg||$224|
|031-73||Ghrelin (1-11) amide (Human)||100 µg||$163|
|T-031-73||Ghrelin (1-11) amide (Human) - I-125 Labeled||10 µCi||$723|
|031-39||Ghrelin (1-14) (Human)||100 µg||$133|
|031-40||Ghrelin (1-14) (Human)||100 µg||$66|
|031-71||Ghrelin (1-14) amide (Human)||100 µg||$163|
|T-031-71||Ghrelin (1-14) amide (Human) - I-125 Labeled||10 µCi||$723|
|031-47||Ghrelin (1-18) / Motlin-Related Peptide (Human)||100 µg||$153|
|031-48||Ghrelin (1-18) / Motlin-Related Peptide (Rat, Mouse)||100 µg||$153|
|031-68||Ghrelin (1-18) amide (Human)||100 µg||$214|
|B-031-68||Ghrelin (1-18) amide (Human) - Biotin Labeled||10 µg||$306|
|FG-031-68A||Ghrelin (1-18) amide (Human) - FAM Labeled||1 nmol||$306|
|T-031-68||Ghrelin (1-18) amide (Human) - I-125 Labeled||10 µCi||$723|
|FR-031-68||Ghrelin (1-18) amide (Human) - Rhodamine Labeled||1 nmol||$357|