Differential expression of ghrelin and its receptor (GHS-R1a) in various adrenal tumors and normal adrenal gland

The role of endocrine hormones in the pathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common spinal deformity characterized by changes in the three-dimensional structure of the spine. It usually initiates during puberty, the peak period of human growth when the secretion of numerous hormones is changing, and it is more common in females than in males. Accumulating evidence shows that the abnormal levels of many hormones including estrogen, melatonin, growth hormone, leptin, adiponectin and ghrelin, may be related to the occurrence and development of AIS. The purpose of this review is to provide a summary and critique of the research published on each hormone over the past 20 years, and to highlight areas for future study. It is hoped that the presentation will help provide a better understanding of the role of endocrine hormones in the pathogenesis of AIS.

The 3PAs: An Update on the Association of Pheochromocytomas, Paragangliomas, and Pituitary Tumors

Pituitary adenomas (PA) and pheochromocytomas/paragangliomas (PHEO/PGL) are rare tumors. Although they may co-exist by coincidence, there is mounting evidence that genes predisposing in PHEO/PGL development, may play a role in pituitary tumorigenesis. In 2012, we described a GH-secreting PA caused by an SDHD mutation in a patient with familial PGLs and found loss of heterozygosity at the SDHD locus in the pituitary tumor, along with increased hypoxia-inducible factor 1α (HIF-1α) levels. Additional patients with PAs and SDHx defects have since been reported. Overall, prevalence of SDHx mutations in PA is very rare (0.3-1.8% in unselected cases) but we and others have identified several cases of PAs with PHEOs/PGLs, like our original report, a condition which we termed the 3 P association (3PAs). Interestingly, when 3PAs is found in the sporadic setting, no SDHx defects were identified, whereas in familial PGLs, SDHx mutations were identified in 62.5-75% of the reported cases. Hence, pituitary surveillance is recommended among patients with SDHx defects. It is possible that the SDHx germline mutation-negative 3PAs cases may be due to another gene, epigenetic changes, mutations in modifier genes, mosaicism, somatic mutations, pituitary hyperplasia due to ectopic hypothalamic hormone secretion or a coincidence. PA in 3PAs are mainly macroadenomas, more aggressive, more resistant to somatostatin analogues, and often require surgery. Using the Sdhb +/- mouse model, we showed that hyperplasia may be the first abnormality in tumorigenesis as initial response to pseudohypoxia. We also propose surveillance and follow-up approach of patients presenting with this association.

Ghrelin as a potential molecular marker of adrenal carcinogenesis: In vivo and in vitro evidence

CONTEXT

Adrenal tumours belong to one of the most prevalent neoplasms. It is a heterogeneous group with different aetiology, clinical manifestation and prognosis. Its histopathologic diagnosis is difficult and identification of differentiation markers for tumorigenesis is extremely valuable for diagnosis.

DESIGN

To assess ghrelin expression and the relationship among ghrelin, IGF2 and the clinicopathological characteristics of adrenal tumours. To investigate the influence of ghrelin on ACC cell line proliferation.

MATERIALS AND METHODS

Expression of ghrelin and IGF2 in a total of 84 adrenal tissue samples (30 adenoma, 12 hyperplasia, 8 myelolipoma, 20 pheochromocytoma, 7 carcinoma and 7 unchanged adrenal glands) were estimated. Every operated patient from whom samples were obtained underwent clinicopathological analysis. All the parameters were compared among the groups examined and correlations between these were estimated. H295R cell line was incubated with ghrelin to assess its effect on proliferation and migration rate.

RESULTS

The highest ghrelin expression was observed in carcinoma samples and the lowest in the control group. Ghrelin expression was 21 times higher in carcinoma (P = .017) and 2.4 times higher in adenoma (P = .029) compared with controls. There were no statistically significant differences between myelolipoma (P = .093) and pheochromocytoma (P = .204) relative to the control. Ghrelin level was significantly higher in carcinoma compared to adenoma (P = .049) samples. A positive correlation between ghrelin and IGF2 expression was observed only in myelolipoma (P = .001). Ghrelin at concentrations of 1 × 10^-6  mol/L and 1 × 10^-8  mol/L significantly stimulated proliferation and migration rate in the H295R cell line.

CONCLUSION

Ghrelin appears to be an essential factor in driving adrenal tumours development.

Distribution and morphology of ghrelin immunostained cells in the adrenal gland of the African ostrich

Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor. We investigated the distribution and morphological characteristics of ghrelin-immunopositive (ghrelin-ip) cells in the African ostrich adrenal gland. We found that the adrenal gland of the African ostrich consisted of three parts: capsule, inter-renal tissue and chromaffin cells. The inter-renal tissue and chromaffin cells interdigitated irregularly. The inter-renal tissue consisted of a peripheral zone and a central inner zone. The peripheral zone could be divided into an outer subcapsular zone and an inner zone. The subcapsular zone cells were arranged as a bow, while the inner area cells formed cords that were perpendicular to the capsule. The central inner zone exhibited irregular clumps and the cells were morphologically similar to chromaffin cells. Ghrelin-ip cells were located throughout the adrenal gland except the capsule. The majority of ghrelin-ip cells were found among the chromaffin cells. The number of ghrelin-ip cells in the inter-renal tissue decreased gradually from the central inner zone, to the inner zone to the subcapsular zone. The ghrelin-ip cells were oval or irregular in shape and exhibited cytoplasmic staining. Our findings suggest that ghrelin may play a role in regulating adrenal hormone secretion in the African ostrich.

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

Ghrelin is a 28-amino acid acylated hormone, highly expressed in the stomach, which binds to its cognate receptor (GHSR1a) to regulate a plethora of relevant biological processes, including food intake, energy balance, hormonal secretions, learning, inflammation, etc. However, ghrelin is, in fact, the most notorious component of a complex, intricate regulatory system comprised of a growing number of alternative peptides (e.g. obestatin, unacylated ghrelin, and In1-ghrelin, etc.), known (GHSRs) and, necessarily unknown receptors, as well as modifying enzymes (e.g. ghrelin-O-acyl-transferase), which interact among them as well as with other regulatory systems in order to tightly modulate key (patho)-physiological processes. This multiplicity of functions and versatility of the ghrelin system arise from a dual, genetic and functional, complexity. Importantly, a growing body of evidence suggests that dysregulation in some of the components of the ghrelin system can lead to or influence the development and/or progression of highly concerning pathologies such as endocrine-related tumors, inflammatory/cardiovascular diseases, and neurodegeneration, wherein these altered components could be used as diagnostic, prognostic, or therapeutic targets. In this context, the aim of this review is to integrate and comprehensively analyze the multiple components and functions of the ghrelin system described to date in order to define and understand its biological and (patho)-physiological significance.

The ghrelin axis--does it have an appetite for cancer progression?

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHSR), is a peptide hormone with diverse physiological roles. Ghrelin regulates GH release, appetite and feeding, gut motility, and energy balance and also has roles in the cardiovascular, immune, and reproductive systems. Ghrelin and the GHSR are expressed in a wide range of normal and tumor tissues, and a fluorescein-labeled, truncated form of ghrelin is showing promise as a biomarker for prostate cancer. Plasma ghrelin levels are generally inversely related to body mass index and are unlikely to be useful as a biomarker for cancer, but may be useful as a marker for cancer cachexia. Some single nucleotide polymorphisms in the ghrelin and GHSR genes have shown associations with cancer risk; however, larger studies are required. Ghrelin regulates processes associated with cancer, including cell proliferation, apoptosis, cell migration, cell invasion, inflammation, and angiogenesis; however, the role of ghrelin in cancer is currently unclear. Ghrelin has predominantly antiinflammatory effects and may play a role in protecting against cancer-related inflammation. Ghrelin and its analogs show promise as treatments for cancer-related cachexia. Further studies using in vivo models are required to determine whether ghrelin has a role in cancer progression.

Evidence suggesting that ghrelin O-acyl transferase inhibitor acts at the hypothalamus to inhibit hypothalamo-pituitary-adrenocortical axis function in the rat

Production of n-octanoyl-modified ghrelin (GHREL), an active form of the peptide requires prohormone processing protease and GHREL O-acyltransferase (GOAT), as well as n-octanoic acid. Recently a selective GOAT antagonist (GO-CoA-Tat) was invented and this tool was used to study the possible role of endogenous GHREL in regulating HPA axis function in the rat. Administration of GOAT inhibitor (GOATi) resulted in a notable decrease in plasma ACTH, aldosterone and corticosterone concentrations at min 60 of experiment. Octanoic acid (OA) administration had no effect on levels of studied hormones. Plasma levels of unacylated and acylated GHREL remained unchanged for 60min after either GOATi or OA administration. Under experimental conditions applied, no significant changes were observed in the levels of GOAT mRNA in hypothalamus, pituitary, adrenal and stomach fundus. After GOATi injection hypothalamic CRH mRNA levels were elevated at 30 min and pituitary POMC mRNA levels at 60 min. Both GOATi and OA lowered basal, but not K(+)-stimulated CRH release by hypothalamic explants and had no effect on basal or CRH-stimulated ACTH release by pituitary slices. Neither GOATi nor OA affected corticosterone secretion by freshly isolated or cultured rat adrenocortical cells. Thus, results of our study suggest that in the rat endogenous GHREL exerts tonic stimulating effect on hypothalamic CRH release. This effect could be demonstrated by administering rats with selected inhibitor of ghrelin O-acyltransferase, the enzyme responsible for GHREL acylation, a process which is absolutely required for both GHSR-1a binding and its central endocrine activities.

Succinate dehydrogenase (SDH) D subunit (SDHD) inactivation in a growth-hormone-producing pituitary tumor: a new association for SDH?

BACKGROUND

Mutations in the subunits B, C, and D of succinate dehydrogenase (SDH) mitochondrial complex II have been associated with the development of paragangliomas (PGL), gastrointestinal stromal tumors, papillary thyroid and renal carcinoma (SDHB), and testicular seminoma (SDHD).

AIM

Our aim was to examine the possible causative link between SDHD inactivation and somatotropinoma.

PATIENTS AND METHODS

A 37-yr-old male presented with acromegaly and hypertension. Other family members were found with PGL. Elevated plasma and urinary levels of catecholamines led to the identification of multiple PGL in the proband in the neck, thorax, and abdomen. Adrenalectomy was performed for bilateral pheochromocytomas (PHEO). A GH-secreting macroadenoma was also found and partially removed via transsphenoidal surgery (TTS). Genetic analysis revealed a novel SDHD mutation (c.298_301delACTC), leading to a frame shift and a premature stop codon at position 133 of the protein. Loss of heterozygosity for the SDHD genetic locus was shown in the GH-secreting adenoma. Down-regulation of SDHD protein in the GH-secreting adenoma by immunoblotting and immunohistochemistry was found. A literature search identified other cases of multiple PGL and/or PHEO in association with pituitary tumors.

CONCLUSION

We describe the first kindred with a germline SDHD pathogenic mutation, inherited PGL, and acromegaly due to a GH-producing pituitary adenoma. SDHD loss of heterozygosity, down-regulation of protein in the GH-secreting adenoma, and decreased SDH enzymatic activity supports SDHD's involvement in the pituitary tumor formation in this patient. Older cases of multiple PGL and PHEO and pituitary tumors in the literature support a possible association between SDH defects and pituitary tumorigenesis.

Adipokines and cardiovascular risk in Cushing's syndrome

Cushing's syndrome (CS) is associated with increased cardiovascular morbidity and mortality. Recent evidence also suggests that increased cardiovascular risk may persist even after long-term remission of CS. Increased central obesity, a typical feature of CS, is associated with altered production of adipokines, which contributes to the pathogenesis of several metabolic and cardiovascular complications observed in this condition. In vitro and in vivo studies have shown a relationship between cortisol and adipokines in several experimental settings. In patients with either active or 'cured' CS, an increase in leptin and resistin levels as well as the release of pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin-6, may be associated with increased cardiovascular risk. For other adipokines, including adiponectin, results are inconclusive. Studies are needed to further elucidate the interactions between clinical and subclinical increases in cortisol production and altered adipokine release in CS.

Ghrelin and cancer

Ghrelin is a peptide hormone that was originally isolated from the stomach as the endogenous ligand for the growth hormone secretagogue receptor (GHSR). Ghrelin has many functions, including the regulation of appetite and gut motility, growth hormone release from the anterior pituitary and roles in the cardiovascular and immune systems. Ghrelin and its receptor are expressed in a number of cancers and cancer cell lines and may play a role in processes associated with cancer progression, including cell proliferation, apoptosis, and cell invasion and migration.

Ghrelin in obesity and endocrine diseases

Ghrelin shows orexigenic effect through its action on the hypothalamic appetite-regulating pathways, while in the periphery ghrelin increases adipose tissue accumulation and has a diabetogenic effect on the liver and pancreas. Adenosine monophosphate-activated protein kinase (AMPK) has been suggested as one of the mediators of ghrelin's effects. Plasma ghrelin levels are dependent on body mass index as well as food intake patterns. Ghrelin levels are in general reduced in obese individuals and in subjects with insulin resistance. In contrast to other forms of obesity, patients with Prader-Willi syndrome (PWS) display high levels of ghrelin, reduced visceral adiposity and relative hypoinsulinemia. Relationships between obesity and common genomic variants of GHRL and GHS-R genes have been studied. Ghrelin may have a role in the weight-reducing effect of bariatric surgery; however, this is a much debated issue. Altered ghrelin levels have also been observed in Cushing's syndrome and thyroid disease probably due to the secondary insulin resistance in these subjects.

68Ga-DOTATOC PET/CT and somatostatin receptor (sst1-sst5) expression in normal human tissue: correlation of sst2 mRNA and SUVmax

PURPOSE

By targeting somatostatin receptors (sst) radiopeptides have been established for both diagnosis and therapy. For physiologically normal human tissues the study provides a normative database of maximum standardized uptake value (SUV(max)) and sst mRNA.

METHODS

A total of 120 patients were subjected to diagnostic (68)Ga-DOTATOC positron emission tomography (PET)/CT (age range 19-83 years). SUV(max) values were measured in physiologically normal tissues defined by normal morphology, absence of surgical intervention and absence of metastatic spread during clinical follow-up. Expression of sst subtypes (sst1-sst5) was measured independently in pooled adult normal human tissue by real-time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

SUV(max) revealed a region-specific pattern (e.g., mean ± SD, spleen 31.1 ± 10.9, kidney 16.9 ± 5.3, liver 12.8 ± 3.6, stomach 7.0 ± 3.1, head of pancreas 6.2 ± 2.3, small bowel 4.8 ± 1.8, thyroid 4.7 ± 2.2, bone 3.9 ± 1.3, large bowel 2.9 ± 0.8, muscle 2.1 ± 0.5, parotid gland 1.9 ± 0.6, axillary lymph node 0.8 ± 0.3 and lung 0.7 ± 0.3). SUV(max) was age independent. Gender differences were evident within the thyroid (female/male: 3.7 ± 1.6/5.5 ± 2.4, p < 0.001; Mann-Whitney U test) and the pancreatic head (5.5 ± 1.9/6.9 ± 2.2, p < 0.001). The sst mRNA was widely expressed and heterogeneous, showing sst1 to be most abundant. SUV(max) values exclusively correlated with sst2 expression (r = 0.846, p < 0.001; Spearman rank correlation analysis), whereas there was no correlation of SUV(max) with the expression of the other four subtypes.

CONCLUSION

In normal human tissues (68)Ga-DOTATOC imaging has been related to the expression of sst2 at the level of mRNA. The novel normative database may improve diagnostics, monitoring and therapy of sst-expressing tumours or inflammation on a molecular basis.

WITHDRAWN: Ghrelin in obesity and endocrine diseases

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi:10.1016/j.mce.2011.02.011. The duplicate article has therefore been withdrawn.

Secretagogue type, sex-steroid milieu, and abdominal visceral adiposity individually determine secretagogue-stimulated cortisol secretion

DESIGN

While androgens and estrogens control glucocorticoid secretion in animal models, how the sex-steroid milieu determines cortisol secretion in humans is less clear. To address this issue, cortisol was measured in archival sera obtained at 10-min intervals for 5 h in 42 healthy men administered double placebo, placebo and testosterone, testosterone and dutasteride (to block 5alpha-reductases type I and type II), or testosterone and anastrozole (to block aromatase) in a double-blind, placebo-controlled, prospectively randomized design.

METHODS

Subjects received i.v. injection of saline, GHRH, GH-releasing peptide-2 (GHRP-2), somatostatin (SS), and GHRP-2/GHRH/l-arginine (triple stimulus) each on separate mornings fasting. Outcomes comprised cortisol concentrations, pulsatile cortisol secretion, and relationships with age or abdominal visceral fat (AVF).

RESULTS

By ANCOVA, baseline (saline-infused) cortisol concentrations (nmol/l) did not differ among the sex-steroid milieus (overall mean 364+/-14). In contrast, stimulated peak cortisol concentrations were strongly determined by secretagogue type (P<0.001) as follows: triple stimulus (868+/-27)>GHRP-2 (616+/-42)>saline=SS=GHRH (grand mean 420+/-21). After GHRP-2 injection, pulsatile cortisol secretion increased with age (R(2)=0.16, P=0.012). After the triple stimulus, pulsatile cortisol secretion correlated i) inversely with serum 5alpha-dihydrotestosterone (DHT) concentrations (R(2)=0.53, P=0.026) and ii) directly with computerized tomography-estimated AVF (R(2)=0.11, P=0.038).

CONCLUSION

Age, DHT concentrations, AVF, and secretagogue type influence pulsatile cortisol secretion at least in men. Further studies should be performed to assess ACTH secretion and native ghrelin action in defined sex-steroid milieus.

Expression of neuropeptide hormone receptors in human adrenal tumors and cell lines: antiproliferative effects of peptide analogues

Peptide analogues targeting various neuropeptide receptors have been used effectively in cancer therapy. A hallmark of adrenocortical tumor formation is the aberrant expression of peptide receptors relating to uncontrolled cell proliferation and hormone overproduction. Our microarray results have also demonstrated a differential expression of neuropeptide hormone receptors in tumor subtypes of human pheochromocytoma. In light of these findings, we performed a comprehensive analysis of relevant receptors in both human adrenomedullary and adrenocortical tumors and tested the antiproliferative effects of peptide analogues targeting these receptors. Specifically, we examined the receptor expression of somatostatin-type-2 receptor, growth hormone-releasing hormone (GHRH) receptor or GHRH receptor splice variant-1 (SV-1) and luteinizing hormone-releasing hormone (LHRH) receptor at the mRNA and protein levels in normal human adrenal tissues, adrenocortical and adrenomedullary tumors, and cell lines. Cytotoxic derivatives of somatostatin AN-238 and, to a lesser extent, AN-162, reduced cell numbers of uninduced and NGF-induced adrenomedullary pheochromocytoma cells and adrenocortical cancer cells. Both the splice variant of GHRH receptor SV-1 and the LHRH receptor were also expressed in adrenocortical cancer cell lines but not in the pheochromocytoma cell line. The GHRH receptor antagonist MZ-4-71 and LHRH antagonist Cetrorelix both significantly reduced cell growth in the adrenocortical cancer cell line. In conclusion, the expression of receptors for somatostatin, GHRH, and LHRH in the normal human adrenal and in adrenal tumors, combined with the growth-inhibitory effects of the antitumor peptide analogues, may make possible improved treatment approaches to adrenal tumors.

Expression of prepro-ghrelin and related receptor genes in the rat adrenal gland and evidences that ghrelin exerts a potent stimulating effect on corticosterone secretion by cultured rat adrenocortical cells

The orexigenic peptide ghrelin (GHREL) and obestatin (OBS) originate from the same peptide precursor, preproghrelin (ppGHREL). Apart from orexigenic effect, GHREL also regulates neuroendocrine function. We investigated GHREL and OBS effects on corticosterone secretion by freshly isolated and cultured rat adrenocortical cells. Classic RT-PCR revealed the presence of ppGHREL, GHS-R1a, GPR39v1 and GPR39v2 and GOAT4 (ghrelin O-acyl transferase) mRNAs in rat adrenals and cultured for 4 days rat adrenocortical cells. Expression of ppGHREL, GHS-R1a, and GOAT genes was notably higher in the cortex than in medulla. High expression level of GOAT gene was found in the zona glomerulosa, while expression level of both GPR39v1 and GPR39v2 genes was similar in adrenal cortical zones and in medulla. In freshly isolated cells neither GHREL nor OBS had an effect on corticosteroid output. Prolonged exposure of cultured cells to GHREL resulted in a potent, comparable to ACTH, stimulating effect of GHREL on corticosterone secretion. Prolonged exposure to OBS was ineffective. Neither GHREL nor OBS had any effect on proliferation of studied cells, while ACTH notably lowered it. GHREL down regulated GHS-R1a gene expression while both ACTH and GHREL stimulated expression level of GPR39v1 gene. Expression of CYP11A1 gene was notably stimulated and that of StAR gene remained unaffected by ACTH or GHREL. Thus, our study is the first to demonstrate direct stimulating effect of GHREL on corticosterone output by cultured rat adrenocortical cells. This stimulating action differs from that evoked by ACTH and is not dependent on the presence of functional ACTH receptor.