Molecular Imaging Targeting Corticotropin-releasing Hormone Receptor for Corticotropinoma: A Changing Paradigm

BACKGROUND

Corticotrophin-releasing hormone (CRH) is the major regulator of adrenocorticotrophic hormone (ACTH) secretion from the anterior pituitary and acts via CRH-1 receptors (CRH-1R). Corticotropinoma though autonomous, still retain their responsiveness to CRH and hence, we hypothesize that in vivo detection of CRH-1 receptors on pituitary adenoma using Gallium-68 (68Ga)-tagged CRH can indicate the functionality of adenoma, and combining it with positron emission tomography-computed tomography (PET-CT) can provide requisite anatomical information.

METHODS

Subjects with ACTH-dependent Cushing's syndrome (CS) (n = 27, 24 with Cushing's disease [CD], 3 with ectopic CS [ECS]) underwent 68Ga CRH PET-CT. Two nuclear medicine physicians read these images for adenoma delineation and superimposed them on magnetic resonance imaging (MRI) sella. The information provided was used for intraoperative navigation and compared with operative and histopathological findings.

FINDINGS

68Ga CRH PET-CT correctly delineated corticotropinoma in all the 24 cases of CD, including the 10 cases with adenoma size < 6mm (4 cases were negative on MRI). Corticotropinoma location on 68Ga CRH PET fusion images with MRI were concordant with operative findings and were further confirmed on histopathology. There was no tracer uptake in the pituitary in 2 patients with ECS, while, in another, the diffuse uptake in pituitary suggested ectopic CRH production.

CONCLUSION

68Ga CRH PET-CT represents a novel, noninvasive molecular imaging, targeting CRH receptors that not only delineate corticotropinoma and provides the surgeon with valuable information for intraoperative tumor navigation, but also helps in differentiating a pituitary from an extra-pituitary source of ACTH-dependent CS.

FUNDING

None.

Hair cortisol and cortisone measurements for the diagnosis of overt and mild Cushing's syndrome

OBJECTIVE

Hair cortisol (HF) and cortisone (HE) measurements reflect tissular exposure to cortisol over months and are increased in overt Cushing's syndrome (CS). No data is available in mild CS. We compared the diagnostic performance of HF and HE between patients with overt or mild CS.

DESIGN

Single centre retrospective study.

METHODS

HF&HE were measured by LC-MS/MS in 48 consecutive adult females with Cushing's disease (CD), ectopic ACTH syndrome, secreting adenomas and carcinomas, and adrenal incidentalomas. All had impaired dexamethasone suppression tests. Overt CS (n = 25) was diagnosed in front of specific symptoms, a mean UFC (>1.5 ULN) and increased midnight serum cortisol or salivary cortisol. Mild CS (n = 23) was diagnosed in patients lacking specific symptoms and displaying at least one additional biological abnormality including mildly increased UFC (≤1.5 ULN), increased midnight serum cortisol or salivary cortisol and suppressed plasma ACTH in patients with adrenal tumours. In this study, 84 healthy subjects and obese patients served as controls.

RESULTS

HF and HE showed roughly similar performance in overt CS (92 and 100% sensitivity, 91 and 99% specificity, respectively). HF and HE were lower in mild CS but higher than in controls (P < 0.01). HE was correlated with midnight serum cortisol (P < 0.02) and volume of adrenal incidentalomas (P < 0.04) but not with UFC. HF and HE had 59% and 68% sensitivity, and 79 and 94% specificity, respectively, for the diagnosis of mild CS. Contrary to UFC, both HF and HE were in the range of overt CS in 11/23 patients with mild CS. Patients with mild CS and increased HE required more antihypertensive treatments and showed worser lipid profiles than patients with normal HE.

CONCLUSIONS

HF and HE measurement performed better in overt than in mild CS but is a useful adjunct to diagnose mild CS and to identify adrenocortical incidentalomas responsible for excessive cortisol exposure.

New types of localization methods for adrenocorticotropic hormone-dependent Cushing's syndrome

The management of endogenous Cushing's syndrome (CS) typically involves two key steps: (i) confirmation of autonomous hypercortisolism and (ii) localization of the cause to guide treatment. Adrenocorticotropic hormone (ACTH)-dependent CS is most commonly due to a pituitary corticotrope tumor which may be so small as to evade detection on conventional magnetic resonance imaging (MRI). Although biochemical testing (e.g., corticotropin stimulation; dexamethasone suppression) can provide an indication of the likely origin of ACTH excess, bilateral inferior petrosal sinus catheterization offers greater accuracy to distinguish pituitary-driven CS [Cushing's Disease (CD)] from the ectopic ACTH syndrome [EAS, e.g., due to a bronchial or pancreatic neuroendocrine tumor (NET)]. In patients with CD, 40-50% may not have a pituitary adenoma (PA) readily visualized on standard clinical MRI. In these subjects, alternative MR sequences (e.g., dynamic, volumetric, fluid attenuation inversion recovery) and higher magnetic field strength (7T > 3T > 1.5T) may aid tumor localization but carry a risk of identifying coincidental (non-causative) pituitary lesions. Molecular imaging is therefore increasingly being deployed to detect small ACTH-secreting PA, with hybrid imaging [e.g., positron emission tomography (PET) combined with MRI] allowing precise anatomical localization of sites of radiotracer (e.g., ¹¹C-methionine) uptake. Similarly, small ACTH-secreting NETs, missed on initial cross-sectional imaging, may be detected using PET tracers targeting abnormal glucose metabolism (e.g., ¹⁸F-fluorodeoxyglucose), somatostatin receptor (SSTR) expression (e.g., ⁶⁸Ga-DOTATATE), amine precursor (e.g., ¹⁸F-DOPA) or amino acid (e.g., ¹¹C-methionine) uptake. Therefore, modern management of ACTH-dependent CS should ideally be undertaken in specialist centers which have an array of cross-sectional and functional imaging techniques at their disposal.

The Mechanisms Underlying Autonomous Adrenocorticotropic Hormone Secretion in Cushing's Disease

Cushing’s disease caused due to adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas (ACTHomas) leads to hypercortisolemia, resulting in increased morbidity and mortality. Autonomous ACTH secretion is attributed to the impaired glucocorticoid negative feedback (glucocorticoid resistance) response. Interestingly, other conditions, such as ectopic ACTH syndrome (EAS) and non-neoplastic hypercortisolemia (NNH, also known as pseudo-Cushing’s syndrome) also exhibit glucocorticoid resistance. Therefore, to differentiate between these conditions, several dynamic tests, including those with desmopressin (DDAVP), corticotrophin-releasing hormone (CRH), and Dex/CRH have been developed. In normal pituitary corticotrophs, ACTH synthesis and secretion are regulated mainly by CRH and glucocorticoids, which are the ACTH secretion-stimulating and -suppressing factors, respectively. These factors regulate ACTH synthesis and secretion through genomic and non-genomic mechanisms. Conversely, glucocorticoid negative feedback is impaired in ACTHomas, which could be due to the overexpression of 11β-HSD2, HSP90, or TR4, or loss of expression of CABLES1 or nuclear BRG1 proteins. Genetic analysis has indicated the involvement of several genes in the etiology of ACTHomas, including USP8, USP48, BRAF, and TP53. However, the association between glucocorticoid resistance and these genes remains unclear. Here, we review the clinical aspects and molecular mechanisms of ACTHomas and compare them to those of other related conditions.

The Clinical Features and Molecular Mechanisms of ACTH-secreting Pancreatic Neuroendocrine Tumors

OBJECTIVE

Pancreatic neuroendocrine tumors (pNETs) causing ectopic adrenal corticotropic hormone (ACTH) syndrome (EAS) are rare and aggressive with little known information. We aimed to elucidate the clinical features and molecular mechanisms of pNETs with EAS by methylation analysis.

METHODS

Seven patients with ectopic ACTH-secreting pNETs who were diagnosed at Shanghai Clinical Endocrine and Metabolic Diseases Center and Pancreatic Disease Center in Ruijin Hospital between 2001 and 2019 were enrolled. Twenty patients with ectopic ACTH-secreting thymic neuroendocrine tumors (TNETs) and 7 with nonfunctional pNETs (nf-pNETs) were also enrolled as controls. We collected clinical data and measured POMC promoter CpG methylation.

RESULTS

All 7 patients had elevated ACTH and urinary free cortisol (UFC) levels with positive ACTH staining in the pancreas and were diagnosed with ectopic ACTH-secreting pNET. Of the 7 patients, 6 underwent surgery and 1 underwent transarterial embolization (TAE). Two patients were free of disease after surgery; 2 died within 90 days after surgery; and 3 had metastases and died within 1 year. Compared with ACTH-secreting TNETs, ACTH-secreting pNETs had similar clinical and biochemical features but a significantly poorer prognosis. POMC promoter CpG methylation was significantly lower in ACTH-secreting pNETs than in nf-pNETs and normal pancreas.

CONCLUSIONS

ACTH-secreting pNETs are aggressive and fatal. Surgery is definitively curative for patients with resectable primary tumors without metastasis. Pro-opiomelanocortin (POMC) promoter hypomethylation caused pNETs to produce ACTH. This study further supplements the genetic features of ACTH-secreting NETs.

Multicentric adrenocorticotropic hormone -producing steroid cell tumor of the fallopian tube & broad ligament in a 15 year old girl

Steroid cell tumors occur usually in the ovaries with very few reported cases of extra-ovarian origin. Our patient was a fifteen year old female, complaining from secondary amenorrhea and voice deepening. Values of serum cortisol, DHEA, FSH & LH were normal. Serum Testosterone was elevated while ACTH-pm was markedly elevated. MRI described bilateral solid para-ovarian masses. Exploration revealed two bilateral tubal extraluminal cysts & a right broad ligament cyst which were all excised. Pathological examination led to the diagnosis of steroid cell tumor. Serum testosterone & ACTH returned to normal levels after surgery with subsequent regression of the virilizing symptoms. We can conclude that extra-ovarian steroid cell tumors are extremely rare. They are usually presented with virilizing symptoms and hormonal abnormalities. Surgery is the main line of treatment.

Radiologically defined lipid-poor adrenal adenomas: histopathological characteristics

BACKGROUND

Adrenal lipid-poor adenomas (LPA) are defined by high unenhanced density (≥ 10 HU), and absolute and relative contrast medium washout > 60% and > 40%, respectively, at computerized tomography (CT). To date, no thorough histopathological characterization has been performed in those frequent lesions (one-third of adrenal adenomas). Our aim was to analyze the histopathological characteristics of adrenal LPA.

METHODS

Patients with LPA (n = 57) were selected among consecutive subjects referred for an adrenal incidentaloma or ACTH-independent Cushing syndrome. FluoroDeoxyGlucose-Positron Emission Tomography (FDG-PET) was performed in 37 patients. In patients treated by adrenalectomy (n = 17), Weiss score and Lin-Weiss-Bisceglia score (in tumors composed entirely or predominantly of oncocytes) were calculated.

RESULTS

Radiological parameters did not differ among patients with ACTH-independent Cushing syndrome (n = 6) and those with adrenal incidentalomas associated with primary aldosteronism (n = 2), autonomous cortisol secretion (n = 14), or non-functioning (n = 35). Patients treated by adrenalectomy had larger tumors (28.9 ± 11.2 vs 17.3 ± 8.4 mm, P < 0.001), higher CT unenhanced density (29.1 ± 11.0 vs 23.1 ± 9.0 HU, P = 0.043), and FDG-PET adrenal uptake (9.0 ± 6.4 vs 4.4 ± 2.3 SUV, P = 0.003) than non-operated ones. Oncocytic features > 75% of the tumor were detected in 12/17 cases (70.6%). Five of those showed borderline-malignant histopathological characteristics by Lin-Weiss-Bisceglia score. Among remaining non-oncocytic tumors, 1/5 had a Weiss score ≥ 3. Overall, 6/17 tumors (35.3%) had borderline-malignant potential. Radiological parameters were similar between patients with benign and borderline-malignant tumors.

CONCLUSIONS

Adrenal LPA are a heterogeneous group of tumors, mostly composed of oncocytomas. Up to 1/3 of those tumors may have a borderline-malignant potential at histopathology.

Molecular analysis and literature-based hypothesis of an immunonegative prostate small cell carcinoma causing ectopic ACTH syndrome

Ectopic ACTH syndrome (EAS) due to a prostate small cell carcinoma (SCC) is very rare with only 26 cases reported to date and has a poor prognosis. We here describe another case of this disorder that was clinically typical based on prior reports as it showed hypercortisolemia and severe hypokalemia with multiple metastasis. However, our current case of prostate SCC causing EAS is the first to display negative immunostaining for ACTH despite detectable POMC mRNA expression in the primary lesion. ACTH immunonegativity is thought to be associated with a more aggressive disease course and a poorer prognosis although there are few studies of the underlying mechanisms. We explored two possibilities for this finding in our current patient: aberrant POMC processing prevented immunodetection with an anti-ACTH antibody; and the ACTH content per cell was below the threshold for immunodetection due to its rapid secretion or low synthesis. The aberrant processing theory was thought to be less likely because of immunonegative findings even using anti-POMC/ACTH antibodies. As the plasma ACTH levels in our patient were comparable with those reported for previous immunopositive prostate EAS cases, we speculated that the depletion of ACTH may be caused not only by rapid secretion but also by low production levels as a sign of de-differentiation. De-differentiation may therefore explain the mechanism underlying the negative correlation between immunoreactivity for ACTH in EAS and disease aggressiveness. We believe that our present findings will be of use in future prospective studies aimed at confirming the mechanism of immunonegativity.

The Ectopic Adrenocorticotropic Hormone Syndrome: Rarely Easy, Always Challenging

Despite modern imaging techniques, differentiating ectopic adrenocorticotropic hormone (ACTH) syndrome from pituitary-dependent Cushing's syndrome, Cushing's disease, is especially difficult when well-differentiated carcinoids are the source of ACTH secretion, particularly pulmonary carcinoid tumors. ACTH-secreting pulmonary carcinoids, like the corticotroph adenomas causing Cushing's disease, are often small and difficult to detect, and patients present with a gradual onset of the classical signs and symptoms of Cushing's syndrome, indistinguishable from the presentation of Cushing's disease. Hence, the differential diagnosis relies on a combination of clinical assessment, dynamic biochemical tests, inferior petrosal sinus sampling, and multimodal imaging, each with its own caveats and pitfalls.

Tumour lateralization in Cushing's disease by inferior petrosal sinus sampling with desmopressin

BACKGROUND

Bilateral inferior petrosal sinus sampling (IPSS) with corticotropin-releasing hormone (CRH) is currently the gold standard in the diagnosis of Cushing's disease (CD) and has also been used in tumour lateralization. Our objective was to determine the diagnostic value and lateralization accuracy of IPSS with desmopressin.

METHODS

We retrospectively analysed 91 patients with Cushing's syndrome who had either negative findings on pituitary dynamic enhanced magnetic resonance imaging (MRI) or nonsuppressed high-dose dexamethasone suppression tests (HDDST). Thin-slice thoracoabdominal computed tomography (CT) and octreotide receptor imaging of whole body were also negative to rule out ectopic adrenocorticotropin hormone (ACTH) syndrome. All patients went through IPSS with desmopressin. Afterwards, transsphenoidal pituitary surgery, light microscope pathology and immunohistological staining for ACTH were performed in all patients.

RESULTS

Diagnosis of CD. Among the 91 patients included, 90 were confirmed with CD, of whom 89 had positive IPSS findings, therefore the sensitivity was 98.9%. The one patient who was negative for CD also had negative IPSS findings, therefore the specificity was 100%. Tumour lateralization. Among the 51 patients who were ultimately diagnosed with CD and whose lateralization by IPSS and surgery was either left or right, 37 had IPSS lateralization in concordance with surgery, therefore the concordance rate was 72.5%. Patients in the concordant group had a higher frequency of right lateralization by surgery.

CONCLUSIONS

IPSS with desmopressin is a sensitive approach in the diagnosis of CD and has moderate accuracy in tumour lateralization, making it an alternative choice to IPSS with CRH.

60 YEARS OF POMC: Purification and biological characterisation of melanotrophins and corticotrophins

The remarkable conservation of the primary structures and anatomical location of dogfish α-melanocyte-stimulating hormone (MSH), corticotrophin-like intermediate lobe peptide (CLIP) and adrenocorticotrophic hormone (ACTH) compared with mammals reinforced the tissue-specific processing hypothesis of ACTH peptides in the pituitary gland. The cloning of dogfish pro-opiomelanocortin (POMC) led to the identification of δ-MSH and simultaneously revealed the high conservation of the γ-MSH sequence during evolution. These studies have also shown that β-MSH is much less conserved during evolution and in some species is not even processed from β-LPH. Human pro-γ-MSH potentiates the corticosteroidogenic activity of ACTH and peptides generated from its N-terminal, in particular big-γ-MSH, appear to have adrenal mitogenic activity. Human big-γ-MSH (from the zona intermedia) may also cause the adrenache. The review finishes with a cautionary note with regard to the misdiagnosis of the ectopic ACTH syndrome in which partial processing of ACTH can result in large concentrations of α-MSH and CLIP, which can interfere in the performance of two-site immunoassays, and the problem of the correct disulphide bridge arrangement in synthetic N-POMC peptides is also discussed.

Recurrent acute-onset Cushing's syndrome 6 years after removal of a thymic neuroendocrine carcinoma: from ectopic ACTH to CRH

We describe a rare case of ectopic Cushing's syndrome that recurred 6 years after resection of a thymic neuroendocrine carcinoma. We discuss reasons for the differing clinical presentations, management, hormone profiles, as well as immunopathology. A 41-year-old male developed acute-onset Cushing's syndrome. Clinical presentation and laboratory results were compatible with ectopic adrenocorticotropin hormone (ACTH) production. Computerized tomography (CT) showed a 3.6 cm thymic tumor which was successfully resected. Plasma ACTH (P-ACTH) normalized the first postoperative day. Histopathology demonstrated a well-differentiated neuroendocrine carcinoma with diffuse positivity for ACTH and focal corticotropin-releasing hormone (CRH) reactivity in a few scattered cells. The patient was in remission for 6 years. He then again presented with acute-onset Cushing's syndrome. Fluorine-labeled dihydroxyphenylalanine ((18)F-DOPA) PET/CT showed local uptake in the mediastinum and he underwent repeat resection. However, P-ACTH remained increased (613 ng/l) and 24-h urinary cortisol was 36,720 nmol, suggesting incomplete tumor removal or metastatic spread. Metyrapone treatment was initiated but then withdrawn because the patient spontaneously recovered and cortisol metabolism gradually normalized within 3 weeks. Histopathology demonstrated a recurrent neuroendocrine carcinoma with the same features as the previous lesion but this time CRH was strongly positive in more numerous cells. Normalization of P-ACTH after primary surgery was compatible with ectopic ACTH production. However, the delayed fall in P-ACTH and serum cortisol is compatible with ectopic CRH production and stimulation of pituitary ACTH secretion, which gradually resolved. Although ectopic CRH production is very rare, the unusual dynamics illustrated here should raise the possibility of CRH production by a neuroendocrine tumor.

Differential gene expression profiles of POMC-related enzymes, transcription factors and receptors between non-pituitary and pituitary ACTH-secreting tumors

The differential gene expression of proopiomelanocortin (POMC)-related processing enzymes, transcription factors, and receptors responsible for ACTH secretion between non-pituitary and pituitary ACTH-secreting tumors remains obscure. This study was attempted to determine the gene expression profiles of transcription factors (Tpit, NeuroD1 and IKZF1), proprotein convertase (PC) 1/3 and PC2, and several key receptors linked to ACTH secretion, including corticotrophin releasing hormone receptor (CRHR1), vasopressin receptor 1b (V1bR), somatostatin receptor (SSTR) subtype-2, -5 and dopamine receptor type 2 (D2R) in non-pituitary and pituitary ACTH-secreting tumors. Surgical tissue specimens from carcinoid tumors causing ectopic ACTH syndrome (EAS: n=4) and pituitary tumors causing Cushing's disease (CD: n=13), were subjected to real-time RT-PCR for measurements of each mRNA levels. POMC and CRHR1 mRNA levels in CD were far greater than those in EAS, whereas IKZF1, PC2, SSTR-2 and -5 mRNA levels in EAS were significantly greater than those in CD. NeuroD1, Tpit, PC1/3, V1bR and D2R mRNA levels were comparable between EAS and CD. In conclusion, differential gene expression profiles revealed more abundant mRNA expression in EAS than in CD of 1) IKZF1 with its potential implication of cell differentiation and hormone secretion, 2) PC2 with its possible enhanced processing activity of mature ACTH, and 3) SSTR-2 and -5 with their potential therapeutic application of more selective agonists in EAS patients.

Aberrant expression and modification of silencing mediator of retinoic acid and thyroid hormone receptors involved in the pathogenesis of tumoral cortisol resistance

Ectopic ACTH syndrome (EAS) accounts for 10-15% of cases of Cushing's syndrome and is mostly caused by small cell lung cancers or thymic carcinoids. EAS is characterized by tumoral cortisol resistance, whose underlying mechanism remains unknown. In this study, we reported that silencing mediator of retinoic acid and thyroid hormone receptors (SMRT), a major nuclear corepressor, was aberrantly expressed in ACTH-secreting thymic carcinoids. Overexpression and knockdown of SMRT in the ACTH-secreting AtT-20 cell line demonstrated that SMRT participated in the negative feedback of dexamethasone-mediated suppression of proopiomelanocortin. Posttranslational modification by the small ubiquitin-like modifiers (SUMO), i.e. SUMOylation plays an important role in fine-tuning transcriptional activities. SUMOylation of SMRT was observed in dexamethasone-resistant cell lines. Moreover, overexpression of the deSUMOylation enzyme enhanced the suppression of proopiomelanocortin by dexamethasone in AtT-20 cells. An evolutionarily conserved consensus SUMOylation site was identified close to the histone deacetylase 3 recruiting domain of SMRT, which might interfere with the recruiting process. These results suggested that aberrant expression and modification of SMRT might be involved in the pathogenesis of tumoral cortisol resistance. A therapeutic approach targeting SMRT SUMOylation might be developed for EAS patients.

p21-activated kinase 3 is overexpressed in thymic neuroendocrine tumors (carcinoids) with ectopic ACTH syndrome and participates in cell migration

Thymic carcinoid is an important component of the tumor spectrum causing Ectopic ACTH Syndrome (EAS) and usually carries a poor prognosis. Efforts have been focused on exploring the mechanism of the excessive ACTH production in non-pituitary tumors, whereas few studies have reported the molecular events underlying the tumor progression. In this study, seven patients with ACTH producing thymic carcinoids were enrolled. Of note is that five of them showed either lymph node metastasis, local invasion or distant metastasis. By using cDNA profiling approach, we evaluated the expression of cell adhesion pathway genes and found a remarkable overexpression of p21-activated kinase 3 (PAK3) in all thymic carcinoids which was further confirmed at both transcriptional and translational level. RAC1, an upstream activator of PAK3, was also overexpressed in thymic carcinoids. Overexpression of PAK3 in NIH3T3 cell enhanced cell migration and invasion. Importantly, we observed c-Jun NH(2)-terminal kinase (JNK) was activated in PAK3 transfected cells, and inhibition of JNK activity by SP600125, a JNK pathway inhibitor, abolished PAK3 mediated cell migration. Activation of JNK pathway was also detected in thymic carcinoid with high level of PAK3 expression. Our findings suggested a potential role of PAK3 in the progression of ACTH-producing thymic carcinoid.

The ectopic ACTH syndrome

Ectopic Cushing's syndrome usually relates to the ectopic ACTH syndrome (EAS) and represents ∼20% of ACTH-dependent and ∼10% of all types of Cushing's syndrome (CS). Nearly any neuroendocrine or non-endocrine tumours may be associated with EAS, but the more prevalent tumours are bronchial carcinoids, small cell lung carcinomas, pancreatic carcinoids, thymic carcinoids, medullary carcinomas of the thyroid, and phaeochromocytomas. Occult tumours are highly represented in all the series (12-38%) and constitute the more challenging cases of EAS, requiring long term follow-up. The lack of any completely reliable diagnostic test procedure and imaging to clearly reveal the source of EAS suggests that we should adopt a step-by-step multidisciplinary approach for their diagnosis and therapeutic management. Clinical features are often similar in ACTH-dependent CS, but the rapid onset and progress may suggest an ectopic source. A combination of biochemical tests and imaging studies seems the most appropriate approach for the prompt identification of EAS, even if there are several pitfalls to be avoided along the way. The most appropriate management for cure of EAS, when its source is identified, is surgical excision after controlling the hypercortisolaemia by inhibitors of cortisol secretion and other newer modalities alone or in combination; bilateral adrenalectomy remains an alternative option. Tumour histology, the presence of metastases and the effective control of hypercortisolaemia affect mortality and morbidity. If a source repeatedly fails to be found, the prognosis is often favourable but the identification of a malignant tumour should still be sought during life-long follow-up to avoid the calamity of misdiagnosis.

Inferior petrosal sinus ACTH and prolactin responses to CRH in ACTH-dependent Cushing's syndrome: a single centre experience from the United Kingdom

Inferior petrosal sinus sampling (IPSS) of ACTH with CRH stimulation helps distinguish pituitary ACTH-dependent Cushing's syndrome from the ectopic ACTH syndrome (EAS). The usefulness of the paradoxical response of other pituitary hormones including prolactin to CRH remains controversial. Data from 33 IPSS procedures carried out at the Walton Centre for Neurology and Neurosurgery in Liverpool were analyzed. Patients were selected for this procedure if they had been diagnosed with ACTH dependent Cushing's syndrome and the majority had no obvious pituitary adenoma on Magnetic Resonance Imaging. Satisfactory simultaneous bilateral catheterization was accomplished in 23/33 (success rate 70%). The diagnostic sensitivity of a basal central/peripheral ACTH ratio >2.0 and >3 post-CRH was 94%. In two patients with subsequently confirmed EAS the maximal central/peripheral ACTH ratio was <2.0 on basal samples and did not change following CRH. The maximal central/peripheral prolactin ratio was noted at 5 min post-CRH, coinciding with the maximal central/peripheral ACTH ratio. The intersinus gradient (ISG) of ACTH was paralleled by a consistent ISG of prolactin and in 7 out of 9 patients (with successful bilateral IPSS and unilateral adenomas) the ISG of prolactin correctly lateralized the microadenoma whereas the ISG of ACTH correctly lateralized in 8 out of 9 patients. Neither of the patients with EAS achieved a central/peripheral prolactin ratio >2 in the basal state and >3 post-CRH. Bilateral catheterization of inferior petrosal sinuses can be successful in up to 70% of cases. Prolactin measurements do not have superior lateralizing capability compared with ACTH but may be useful in the differential diagnosis of pituitary-driven from EAS.

Gene expression profiles of thymic neuroendocrine tumors (carcinoids) with ectopic ACTH syndrome reveal novel molecular mechanism

Although there has been increased knowledge about the molecular biology of neuroendocrine tumors (NETs), little is known about thymic carcinoids and even less about those with excessive hormone disorders, such as ectopic ACTH syndrome. This study was designed to gain insights into the molecular networks underlying the tumorigenesis of thymic carcinoids with ACTH secretion. By an approach integrating cDNA microarray and methods of computational biology, we compare gene expression profile between ACTH-producing thymic carcinoids and the normal thymus. In total, there are 63 biological categories increased and 108 decreased in thymic carcinoids. Cell proliferation was stimulated, which may explain the relatively uncontrolled cell growth of the tumor. Dysregulation of the Notch-signaling pathway was likely to be underlying the neuroendocrine features of this type of tumors. Moreover, inhibition of immunity and increased neuropeptide signaling molecules (POMC and its sorting molecule CPE) made the clinical manifestation reasonable and thus validated the array data. In conclusion, thymic carcinoids have a distinct gene expression pattern from the normal thymus, and they are characterized by deregulations of a series of biofunctions, which may be involved in the development of NETs. Hence, this study has provided not only a detailed comprehension of the molecular pathogenesis of thymic carcinoids with ectopic ACTH syndrome, but also a road map to approach thymic NETs at the system level.

Cushing's syndrome associated with a nested stromal epithelial tumor of the liver: hormonal, immunohistochemical, and molecular studies

CONTEXT

Ectopic ACTH syndrome (EAS) is principally associated with aggressive malignant tumors but also with neuroendocrine tumors of good prognosis. Recently, rare nonhepatocytic nested stromal and epithelial tumors (NSET) were characterized by their possible association with Cushing's syndrome of which biochemical and physiopathological features were still incompletely studied.

OBJECTIVE

To describe the clinical and hormonal characteristics of an EAS originating from a liver NSET and further understand the mechanism of cortisol overproduction.

DESIGN AND SETTING

This is a clinical case report from the Endocrinology Department of Caen University Hospital, France.

PATIENT AND INTERVENTION

A 17-year-old female patient was found to have a large liver NSET with mild Cushingoid clinical features and intense biological hypercortisolism but moderate ACTH secretion. Resection of the tumor was curative with a 30-month follow-up.

RESULTS

The epithelial component of the tumor coexpressed ACTH mildly, corticotropin-releasing hormone (CRH) strongly, and 11beta-hydroxysteroid dehydrogenase at a level comparable with normal human hepatocytes.

CONCLUSIONS

Liver NSET is a new cause of EAS, which may evoke hypercortisolism by multiple biochemical pathways.

Association between tumoral GH-releasing peptide receptor type 1a mRNA expression and in vivo response to GH-releasing peptide-6 in ACTH-dependent Cushing's syndrome patients

OBJECTIVE

GH secretagogues (GHS) produce exaggerated ACTH and cortisol responses in Cushing's disease (CD) patients, attributable to their direct action on GH-releasing peptide receptor type 1a (GHSR-1a). However, there are no studies correlating the in vivo response to GHS and GHSR-1a mRNA expression in ACTH-dependent Cushing's syndrome (CS) patients. The aim of this study is to correlate the patterns of ACTH and cortisol response to GH-releasing peptide-6 (GHRP-6) to GHSR-1a expression in ACTH-dependent CS patients.

DESIGN

Prospective study in a tertiary referral hospital center. Fifteen CD patients and two ectopic ACTH syndrome (EAS) patients were studied.

METHODS

Tumor fragments were submitted to RNA extraction, and GHSR-1a expression was studied through real-time qPCR and compared with normal tissue samples. The patients were also submitted to desmopressin test and vasopressin receptor type 1B (AVPR1B) mRNA analysis by qPCR.

RESULTS

GHSR-1a expression was similar in normal pituitary samples and in corticotrophic tumor samples. GHSR-1a expression was higher in patients (CD and EAS) presenting in vivo response to GHRP-6. Higher expression of AVPR1B was observed in the EAS patients responsive to desmopressin, as well as in corticotrophic tumors, as compared with normal pituitary samples, but no correlation between AVPR1B expression and response to desmopressin was observed in the CD patients.

CONCLUSIONS

Our results revealed a higher expression of GHSR-1a in the ACTH-dependent CS patients responsive to GHRP-6, suggesting an association between receptor gene expression and in vivo response to the secretagogue in both the CD and the EAS patients.

Dopamine receptor expression and function in corticotroph ectopic tumors

BACKGROUND

Dopamine receptor (DR) expression and dopamine agonist (DA) effectiveness have never been demonstrated in neuroendocrine tumors associated with ectopic ACTH syndrome (EAS).

AIM

The aim of the current study was to evaluate DR and particularly D2 subtype expression in neuroendocrine tumors associated with EAS and to evaluate the in vivo effectiveness of the DA cabergoline in the treatment of EAS.

PATIENTS AND METHODS

Six ACTH-secreting neuroendocrine tumors, including four lung, one pancreatic, and one thymic carcinoid, were used for the evaluation of D2 expression by immunohistochemistry. DR subtypes and D2 isoforms and number were evaluated by RT-PCR in three cases of persistent EAS after surgery. These patients were treated with cabergoline at the dose of 3.5 mg/wk for 6 months. Clinical parameters, hormonal levels, and tumor size were monitored during the treatment period.

RESULTS

At immunohistochemistry, D2 was expressed in five (83.3%) tumors. At RT-PCR, D2 was confirmed in all three cases but at variable numbers, whereas D4 was expressed in two cases. D(2long) was expressed in all three cases, together with D(2short) in one case. A normalization of urinary cortisol levels was found in two patients (66.7%) after 3 months of treatment. However, treatment escape was demonstrated in one of these patients afterward.

CONCLUSION

The results of this study demonstrated that DR are expressed in neuroendocrine tumors associated with EAS and that cabergoline treatment could be effective in controlling cortisol excess in a subgroup of patients with EAS. Further studies on a larger number of patients are mandatory to confirm the usefulness of DA in EAS.

HPLC-RIA analysis of the ectopic cortisol production in a cancerous pancreas tumor

Steroidal pathophysiology of a malignant, ACTH-producing pancreas tumor was investigated via HPLC-RIA determinations of intratissular concentrations of eleven main steroid hormones. The tumor specimen underwent extraction procedure with ethyl acetate and the extract was purified on a C18 minicolumn. Steroids were isolated by HPLC (C18-silica reversed phase stationary phase and methanol-water eluent system) and quantified by specific RIAs. Cortisol content of the tumor specimen was 15,700 pmol/g, the further steroid hormones were found in much lower concentrations (< 1.5-28 pmol/g). The extremely high cortisol concentration in the tissue witnesses the synthesis of the main glucocorticoid steroid in the ACTH-producing pancreas tumor and suggests a stimulating paracrine effect of ACTH on cortisol production. The present data verify that the determination of intratissular steroid concentrations by HPLC-RIA methods may identify even the most peculiar hormone sources and the hormone profiles facilitate studying pathophysiology of ectopic endocrine tumors.

RT-PCR analysis of corticotroph-associated genes expression in carcinoid tumours in the ectopic-ACTH syndrome

OBJECTIVE

ACTH is frequently produced in non-pituitary tumours, leading to the ectopic-ACTH syndrome, but the molecular mechanisms of its expression remain obscure. This study was aimed at understanding the transcription mechanisms of the ACTH-precursor gene in carcinoid tumours of the lung or thymus.

DESIGN

Transcripts coding for a series of corticotroph-associated transcription factor genes were detected, together with markers of the corticotroph phenotype. We studied a series of 41 carcinoid tumours including 15 with proven ectopic-ACTH syndrome.

METHODS

Specific RT-PCR reactions were designed for each gene including alternatively spliced isoforms.

RESULTS

The markers of the corticotroph phenotype were detected in all ACTH-positive tumours. Expression of the Tpit and Pitx1 genes were not restricted to ACTH-positive tumours but were also detected in many ACTH-negative carcinoids. Only a subset of ACTH-negative tumours expressed NAK-1/Nur77, and NeuroD1 expression was detected in approximately 50% of the tumours regardless of their secretory status. The glucocorticoid receptor alpha was detected in every tumour in contrast to its beta isoform detectable in a few tumours only. Chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) and peroxisome proliferator-activated receptor (PPAR) gamma2 were expressed in 50% of the tumours of each group whereas PPARgamma1 was expressed in almost every tumour.

CONCLUSIONS

ACTH-positive carcinoids do not share a characteristic expression pattern of the corticotroph-associated transcription factor genes, suggesting that the transcriptional mechanisms of the ACTH-precursor gene differ from those in normal pituitary corticotrophs. Expression of Tpit and Pitx1 genes in most carcinoids suggests that some aspects of the pituitary corticotroph phenotype may belong to general carcinoid differentiation.

Hypomethylation in the promoter region of POMC gene correlates with ectopic overexpression in thymic carcinoids

The ectopic ACTH syndrome is caused by abnormal expression of the POMC gene product arising from non-pituitary tumors in response to the ectopic activation of the pituitary-specific promoter of this gene. It has been proved that methylation of the CpG island in the promoter region is associated with silencing of some genes. Using bisulphite sequencing, we identified hypermethylation in the 5' promoter region of the POMC gene in three normal thymuses and one large cell lung cancer, and hypomethylation in five thymic carcinoid tumors resected from patients with ectopic ACTH syndrome. The region undergoing hypermethylation was narrowed to coordinates -417 to -260 of the POMC promoter. Furthermore, we observed that the levels of POMC expression correlated with the methylation density at -417 to -260 bp across the E2 transcription factor binding region of the POMC promoter. It is concluded that hypomethylation of the POMC promoter in thymic carcinoids correlates with POMC overexpression and the ectopic ACTH syndrome.

Midnight salivary cortisol for the initial diagnosis of Cushing's syndrome of various causes

We assessed the value of midnight salivary cortisol for the initial diagnosis of Cushing's syndrome. Sixty-three patients with various causes of Cushing's syndrome (37 with Cushing's disease, 17 with adrenal Cushing's syndrome, and nine with ectopic ACTH syndrome) and 54 control subjects with simple obesity were studied. All patients with Cushing's syndrome excreted more than 90 microg urinary free cortisol (UFC)/d (248 nmol/d), and all controls excreted less than 90 microg/d UFC. All patients with Cushing's syndrome had a midnight salivary cortisol concentration above 2.0 ng/ml (5.52 nmol/liter), whereas only three controls did so [2.0 ng/ml (5.52 nmol/liter); 2.05 ng/ml (5.66 nmol/liter); and 3.6 ng/ml (9.96 nmol/liter)]. This cut-off provides a sensitivity of 100% and a specificity of 96%. In patients with Cushing's syndrome, midnight salivary cortisol concentrations were correlated with UFC collected over the same period of time (0800-0800 h). Salivary cortisol measurements taken every 4 h showed a typical lack of circadian variation. The daily measurement of midnight salivary cortisol concentrations for 2 wk or more in five other out-patients (with obvious Cushing's disease, subclinical adrenal Cushing's syndrome, suspected Cushing's syndrome, pituitary incidentaloma, and prolactinoma) demonstrated the clinical utility of this factor. Measuring midnight salivary cortisol is an easy and noninvasive means of diagnosing hypercortisolism. Its diagnostic accuracy is identical to, if not better than, that of previously described gold standards.

Proopiomelanocortin gene expression and DNA methylation: implications for Cushing's syndrome and beyond

Proopiomelanocortin gene (POMC) is recognised as playing an important role in the regulation of the hypothalamo-pituitary-adrenal axis, adrenal development and obesity. POMC is activated in ACTH-dependent Cushing's syndrome. The syndrome may occur when the highly tIssue-specific 5' promoter of human POMC is activated in pituitary and non-pituitary sites. Whilst the factors involved in transcription in the corticotrophs of the anterior pituitary gland are becoming well delineated, the mechanism of activation in non-pituitary sites is not fully understood. This promoter is embedded within a defined CpG island, and, in contrast to somatically expressed CpG island promoters reported to date, is methylated in normal non-expressing tIssues, but is specifically unmethylated in expressing tIssues, tumours and the POMC-expressing DMS-79 small-cell lung cancer cell line. Methylation in vitro is sufficient for silencing of expression. In particular, methylation near the response element for the tIssue-specific POMC activator PTX1, diminishes POMC expression. Sites outside the PTX1 response element may be important for binding, and this may have implications for pituitary development. DMS-79 cells lack POMC-demethylating activity, implying that the methylation and expression patterns are likely to be set early or prior to neoplastic transformation, and that targeted de novo methylation might be a potential therapeutic strategy. It is conceivable that in POMC neurons of the hypothalamus the POMC promoter is subject to a variable density of methylation with clear implications for the signalling of satiety and obesity.

Ectopic ACTH syndrome: discrepancy between somatostatin receptor status in vivo and ex vivo, and between immunostaining and gene transcription for POMC and CRH

OBJECTIVE

To characterize somatostatin receptor status in vivo and ex vivo and immunoreactivity and gene transcription for proopiomelanocortin (POMC) and corticotropin-releasing hormone (CRH) in a case of Cushing's syndrome caused by a sporadic metastatic medullary thyroid carcinoma (MTC).

METHODS

(111)In octreoscan, analysis of tumorous mRNA transcripts for somatostatin receptor subtypes (SSTR) as well as for POMC and CRH.

RESULTS

The tissue was intensely positive by (111)In octreoscan but expressed only SSTR 1, 3 and 5. There was immunopositivity only for CRH, but gene transcription for both POMC and CRH was seen.

CONCLUSIONS

(1) This first comparison between somatostatin receptor status in vivo and ex vivo in MTC shows a marked positive octreoscan despite absent SSTR 2 expression, and (2) this is the first report of a discrepancy between immunostaining and gene transcription for POMC and CRH.

The desmopressin and combined CRH-desmopressin tests in the differential diagnosis of ACTH-dependent Cushing's syndrome: constraints imposed by the expression of V2 vasopressin receptors in tumors with ectopic ACTH secretion

The role of desmopressin, alone or in combination with CRH, in the differential diagnosis between Cushing's disease (CD) and ectopic ACTH secretion (EAS) still remains uncertain. Based on existing data, the desmopressin test is regarded as an alternative to the CRH stimulation test and, when given in combination with CRH, it has been suggested to completely discriminate between patients with CD and EAS. However, assessment of these tests has been limited in only a small number of patients with EAS. Desmopressin is a relatively specific V2 vasopressin receptor (V2R) agonist. Although expression of V3 vasopressin receptor (V3R) is common in tumors with EAS, the expression of V2R has not been extensively investigated. In the present study, we report our findings of the desmopressin and the combined CRH-desmopressin test in a series of patients with CD and EAS; also, the expression of V2R and V3R was investigated in tumors with EAS by a RT-PCR method. We assessed a cohort of 31 patients with ACTH-dependent Cushing's syndrome, including 26 patients with CD and five cases with histologically confirmed EAS. To avoid bias of predetermined criteria, univariate curves of the receiver operating characteristics (ROC) were constructed by plotting the sensitivity against 1-specificity at each level of the percent cortisol (F) and ACTH responses to these tests. Following desmopressin administration there was an overlap of the percent F and ACTH responses among patients with CD and EAS, and the area under the ROC curve for both these responses was not significantly different than that occurring by chance. This was also true for the percent F response following the combined CRH-desmopressin test. However, the area under the ROC curve for the percent ACTH rise following the combined test was significantly different; the point of the ROC curve closest to 1 corresponded to a percent ACTH rise of 218% (88% sensitivity and 80% specificity). Expression of V2R and V3R mRNA was investigated in four of the five excised tumors with EAS and revealed the presence of the V2R in all, whereas the V3R mRNA was expressed in three of these cases. In conclusion, in this series the desmopressin test produced a significant overlap of responses between CD and patients with EAS and, therefore, is of limited value in the differential diagnosis of the ACTH-dependent Cushing's syndrome. This is most probably due to the expression of the V2R in tumors with EAS. Moreover, following the combined CRH-desmopressin test only the ACTH but not the F responses were diagnostically useful, but still far from completely discriminating patients with CD and EAS.

Suprasellar adrenocorticotropic hormone-secreting ectopic pituitary adenoma: case report and literature Review

OBJECTIVE AND IMPORTANCE

Functional ectopic pituitary adenomas are rare and can be misdiagnosed as extensions of pituitary adenomas when they are located in the vicinity of the normal gland. In this report, we present a case of an ectopic adrenocorticotropic hormone-secreting suprasellar pituitary adenoma that caused Cushing's disease. A literature review of previously reported ectopic pituitary adenomas is included to illustrate the diverse clinical manifestations of this disease entity.

CLINICAL PRESENTATION

An 11-year-old boy was noted to have hirsutism, a buffalo hump, and unexplained weight gain consistent with Cushing's syndrome. Laboratory investigations revealed that the boy had elevated adrenocorticotropic hormone and serum cortisol levels unsuppressed by dexamethasone. Magnetic resonance imaging scans were suggestive of a pituitary adenoma with suprasellar extension.

INTERVENTION

The initial transsphenoidal approach failed to achieve complete surgical resection. A repeat operation in which the pterional approach was used revealed a suprasellar pituitary adenoma without association with intrasellar contents. The patient's cushingoid symptoms improved significantly 3 months after surgery.

CONCLUSION

Ectopic pituitary adenomas should be considered in the differential diagnosis for all patients with Cushing's syndrome. Furthermore, surgical approaches should be chosen carefully once the diagnosis of ectopic pituitary adenoma is made.

[Severe metabolic alkalosis following hypokalemia from a paraneoplastic Cushing syndrome]

Metabolic alkalosis is frequently observed in critically ill patients. Etiologies are numerous but endocrinal causes are rare. We report a case of a patient with severe respiratory insufficiency, metabolic alkalosis and hypokalemia. The evolution was fatal. Further explorations revealed an ectopic Adrenocorticotropine Hormone syndrome. The initial tumor was probably a small cell lung carcinoma.

Androgen secretion in ectopic ACTH syndrome and in Cushing's disease: modifications before and after surgery

The role of ACTH in the control of adrenal androgen secretion is known, although the possible existence of other regulatory factors has been also suggested. While some data concerning Cushing's disease have been reported, only few studies concerned androgen levels in ectopic ACTH secretion. The aim of this study was to evaluate serum DHEA-S, androstenedione (A) and testosterone (T) levels in 36 women with ACTH-dependent Cushing's syndrome (30 with Cushing's disease and 6 with ectopic ACTH secretion) before and after surgery. Two men with ectopic ACTH production were also studied. In 30 women with Cushing's disease serum DHEA-S (9.6 +/- 0.9 micromol/l), A (15.2 +/- 1.2 nmol/l) and T (4.1 +/- 0.5 nmol/l) were higher than in controls (p < 0.01): elevated DHEA-S, A and T values were found in 8, 18 and 17 cases, respectively. After adenomectomy in 15 apparently cured patients DHEA-S, A and T levels were low at 1 - 3 months and at 6 - 12 months after surgery. At 18 - 24 months, DHEA-S remained low in spite of cortisol normalisation. In ectopic Cushing's syndrome, A levels were significantly higher (23.1 +/- 4.9 nmol/l) than in Cushing's disease (p < 0.05), while no differences were found in DHEA-S and T levels. Two patients had elevated DHEA-S values, 3 women had high T levels and 7 of the 8 patients had very high A concentration that was lowered in 3 operated cases. In conclusion, the pattern of adrenal androgen secretion is rather different in patients with pituitary or with ectopic Cushing's syndrome. While the frequency of DHEA-S and T alterations is similar, androstenedione secretion is greatly increased in the latter condition. It is suggested that in ACTH-secreting non-pituitary tumours, the production of a POMC-derived peptide, although unidentified, may lead to preferentially stimulated androstenedione secretion, without affecting other enzymatic pathways.

Thymic hyperplasia as a source of ectopic ACTH production

A 26 year-old man with suspected Cushing's disease underwent transsphenoidal exploration of the pituitary without any evidence of microadenoma or hyperplasia. Progressive hypercortisolism necessitated bilateral adrenalectomy. Postoperatively, skin pigmentation gradually developed with a marked elevation of plasma ACTH levels, and CT scanning uncovered a thymic mass. Following removal of the thymic mass, skin pigmentation disappeared and plasma ACTH levels fell to normal. The excised mass was found to be a benign thymic hyperplasia without epithelial or carcinoid tumor cells. However, gel chromatography showed that the thymic tissue extract contained high ACTH content comparable to that of ectopic ACTH-producing tumors with a major component corresponding to ACTH(1-39). Northern blot analysis and in situ hybridization revealed the expression of proopiomelanocortin transcripts in lymphocytes of thymic hyperplasia. This report suggests that lymphocytes in thymic hyperplasia are the most likely site of deregulated ACTH expression causing ectopic ACTH syndrome.

Ectopic ACTH production by a bronchial carcinoid tumour responsive to desmopressin in vivo and in vitro

A desmopressin-induced ACTH increase has been recently suggested to be specific for pituitary-dependent Cushing's disease. We present the case of a 47-year-old woman with Cushing's syndrome due to ectopic ACTH production by a bronchial carcinoid. While CRH failed to induce an ACTH or cortisol response, intravenous administration of desmopressin led to a 47% increase in serum ACTH and a 42% increase in serum cortisol concentration. After surgical removal of the tumour, the desmopressin response became negative. In vitro, ACTH production by tumour cells obtained at surgery was also stimulated by desmopressin but not by CRH. Additional receptor mRNA expression studies using RT-PCR revealed expression of both V2 and V3 vasopressin receptor subtypes in the carcinoid tumour at a level comparable to that recently described in pituitary corticotroph adenomas. This case illustrates that ACTH stimulation by desmopressin is not specific for pituitary-dependent Cushing's syndrome as vasopressin receptor subtypes known to interact with desmopressin may also be found in ectopic tumours producing ACTH.

Inferior petrosal sinus AVP in patients with Cushing's syndrome

OBJECTIVE

In both normal volunteers and patients with Cushing's disease, one dominant inferior petrosal sinus (IPS) contains higher concentrations of AVP and ACTH than the contralateral (non-dominant) IPS, but ovine corticotrophin-releasing hormone (oCRH)-stimulated AVP in the petrosal sinuses is greater in Cushing's disease than in normal volunteers. To distinguish whether greater oCRH-releasable AVP might be specifically related to the presence of a pituitary corticotrophinoma, or be due to hypercortisolism per se, we compared IPS AVP in patients with Cushing's disease with those of patients with other causes of Cushing's syndrome.

PATIENTS

Twenty-three patients with Cushing's disease, 16 patients with the syndrome of ectopic ACTH and seven patients with Cushing's syndrome of adrenal origin.

MEASUREMENTS

AVP and ACTH, measured both before and 3, 5 and 10 minutes after oCRH in the petrosal sinuses, and in a peripheral vein.

RESULTS

In all three groups, AVP concentrations were lateralized such that most of the AVP was found in one, dominant IPS. oCRH significantly increased IPS ACTH only in patients with Cushing's disease (p < 0.001), whereas it significantly increased dominant IPS AVP levels in all three patient groups (P < 0.01). However, neither dominant nor non-dominant IPS AVP (basal or oCRH-stimulated) were significantly different among patients with Cushing's disease, ectopic ACTH or Cushing's syndrome of adrenal origin. Basal and oCRH-stimulated IPS AVP were negatively correlated with urine free cortisol.

CONCLUSIONS

Inferior petrosal sinus AVP levels are similar in all forms of Cushing's syndrome, and thus the higher inferior petrosal sinus AVP levels in patients with Cushing's disease compared with normal volunteers are unlikely to be related specifically to the presence of the pituitary corticotrophinoma. While AVP may play a role in pituitary corticotroph tumourigenesis or may be secreted by some pituitary corticotroph tumours, the observation that CRH-stimulated inferior petrosal sinus AVP levels are higher in Cushing's disease than in normal volunteers appears most likely to be related to the low endogenous CRH levels induced by hypercortisolism, rather than a consequence of Cushing's disease itself. We hypothesize that low endogenous CRH leads to increased sensitivity of central nervous system CRH receptors to exogenous CRH, and thus to greater ovine CRH-stimulated AVP.

Expression of glucocorticoid receptor gene isoforms in corticotropin-secreting tumors

The molecular basis of Cushing's disease is not known. One of the most characteristic features of such tumors is their resistance to corticosteroid feedback at the pituitary level. We have hypothesized that abnormalities of the glucocorticoid receptor (GR) gene might play a role in the development of Cushing's disease via an increase in the relative production of the nonligand-binding splice variant of the GR, GR beta, known to exert dominant negative effects over the ligand-binding isoform, GR alpha. Alternatively, a change in overall GR expression, or mutations of some functional domains of the GR gene, might be involved in the pathogenesis of corticotroph tumors. We studied 22 tumors (17 pituitary ACTH-secreting tumors, 2 ectopic ACTH-producing tumors, 2 prolactinomas, and 1 nonfunctioning adenoma) and three normal pituitaries. RT-PCR was performed with primers specific to GR alpha and GR beta complementary DNA, followed by Southern blotting using an internal probe, and the ratio of the two bands quantitated by densitometry. We also assessed the overall expression of GR relative to the message of both the POMC gene and a housekeeping gene. Single-strand conformation polymorphism analysis of the DNA-binding domain and splice junction region of the gene was also performed. GR alpha messenger RNA was expressed at 37.3-fold +/- 5.7 (range, 32 to 46) excess, as compared with the GR beta subform. This pattern was observed both in the tumor samples and in the normal pituitaries used as controls. A majority of the ACTH-secreting tumors (16/19), including the ectopic secretors, showed variable but increased overall GR expression, whereas 3 tumors showed an expression approximately equivalent to the normal controls; however, no correlation was found between these two groups and the response to the high-dose dexamethasone test, nor was there any correlation with tumor histology. No mutations were found in any of the tumors by PCR-single-strand conformation polymorphism analysis. In conclusion, although both pituitary and ectopic ACTH-secreting tumors are at least partially glucocorticoid-resistant, no significant abnormalities in the relative expression of the two main GR subforms were observed in a series of such tumors. Additionally, mutations of regions critical to normal function of the receptor do not seem to be a frequent event in these tumors.

11 beta-Hydroxysteroid dehydrogenase and the syndrome of apparent mineralocorticoid excess

Whereas aldosterone is normally a much stronger mineralocorticoid than cortisol in vivo, mineralocorticoid receptors have identical in vitro affinities for these hormones. The in vivo specificity of the receptors is, at least in part, the result of activity of 11-HSD, an enzyme located in most mineralocorticoid target tissues that converts cortisol to cortisone. Cortisone is not a ligand for the receptor, whereas aldosterone is not a substrate of the enzyme. The syndrome of AME is a rare form of juvenile hypertension in which 11-HSD is defective. This deficiency allows mineralocorticoid receptors to be occupied by cortisol, leading to hypertension, because plasma concentrations of cortisol are much higher than those of aldosterone. Licorice, which contains 11-HSD inhibitors, causes a similar syndrome. There are two known isozymes of 11-HSD. The liver or type I isozyme is expressed at high levels in the liver, has a relatively low affinity for steroids (micromolar Km), catalyzes both dehydrogenation and the reverse reductase reaction, and utilizes NADP+ or NADPH as cofactors. The kidney or type 2 isozyme is expressed at high levels in the kidney and placenta, has a high affinity (nanomolar Km) for steroids, catalyzes only dehydrogenation, and utilizes NAD+ as a cofactor. Mutations in the HSD11B2 (HSD11K) gene encoding the kidney isozyme of 11-HSD have been detected in all kindreds with AME studied thus far. This gene represents a candidate locus for the common, "essential" form of hypertension.

Cushing's syndrome secondary to ectopic ACTH secretion from a primary ovarian carcinoma

We report a 63-year-old woman who presented with clinical and biochemical features of ACTH dependent Cushing's syndrome secondary to a primary ovarian carcinoma. The tumour produced very high levels of ACTH precursors, consistent with defective POMC processing.

Somatostatin analogs in ectopic corticotropin production

Eutopic corticotroph pituitary adenomas and adrenal cortisol-producing adenomas do not usually express somatostatin receptors. However, ectopic corticotropin (ACTH)-producing tumors often express somatostatin receptors. Thus, the octreoscan can detect and localize tumors in 80% of patients with ectopic ACTH syndrome, and so it can be used to differentiate between eutopic and ectopic ACTH-dependent bilateral adrenal hyperplasia. Octreotide therapy can produce a rapid and sustained reduction of ACTH and cortisol levels in patients with ectopic ACTH-dependent Cushing's syndrome and, in some, may be the only long-term therapy possible. Although no large series have been reported, a review of the literature reveals a large number of case reports that have demonstrated the effectiveness of octreotide.

The pituitary V3 vasopressin receptor and the corticotroph phenotype in ectopic ACTH syndrome

Ectopic ACTH secretion occurs in highly differentiated and rather indolent tumors like bronchial carcinoids or, in contrast, in various types of aggressive and poorly differentiated neuroendocrine tumors. We explored this phenomenon using the recently cloned human pituitary V3 vasopressin receptor as an alternate molecular marker of the corticotroph phenotype. Expression of V3 receptor, corticotrophin releasing hormone (CRH) receptor, and proopiomelanocortin (POMC) genes was examined in tumors of pituitary and nonpituitary origin. A comparative RT-PCR approach revealed signals for both V3 receptor and CHR receptor mRNAs in 17 of 18 ACTH-secreting pituitary adenomas, and 6 of 6 normal pituitaries; in six growth hormone- or prolactin-secreting adenomas, a very faint V3 receptor signal was observed in three cases, and CRH receptor signal was undetected in all. Six of eight bronchial carcinoids responsible for the ectopic ACTH syndrome had both POMC and V3 receptor signals as high as those in ACTH-secreting pituitary adenomas; in contrast, no POMC signal and only a very faint V3 receptor signal were detected in six of eight nonsecreting bronchial carcinoids. Northern blot analysis showed V3 receptor mRNA of identical size in ACTH-secreting bronchial carcinoids and pituitary tumors. Other types of nonpituitary tumors responsible for ectopic ACTH syndrome presented much lower levels of both POMC and V3 receptor gene expression than those found in ACTH-secreting bronchial carcinoids. In contrast with the V3 receptor, CRH receptor mRNA was detected in the majority of neuroendocrine tumors irrespective of their POMC status. These results show that expression of the V3 receptor gene participates in the corticotroph phenotype. Its striking association with ACTH-secreting bronchial carcinoids defines a subset of nonpituitary tumors in which ectopic POMC gene expression is but one aspect of a wider process of corticotroph cell differentiation, and opens new possibilities of pharmacological investigations and even manipulations of this peculiar ACTH hypersecretory syndrome.

11 beta-Hydroxysteroid dehydrogenase activity in Cushing's syndrome: explaining the mineralocorticoid excess state of the ectopic adrenocorticotropin syndrome

A characteristic feature of the ectopic ACTH syndrome is a state of mineralocorticoid excess, although the etiology remains obscure. Some forms of endocrine hypertension, such as licorice ingestion, have been explained by cortisol acting as a mineralocorticoid in the setting of inhibition or deficiency of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD). This enzyme is responsible for the conversion of cortisol (F) to hormonally inactive cortisone, and its activity in vivo can be inferred from the ratio of the urinary excretion of tetrahydrocortisol (THF) and its isomer (5 alpha THF) to tetrahydrocortisone. Twenty-two patients with Cushing's syndrome (11 pituitary dependent, 9 ectopic, and 2 adrenal adenomas) and 13 controls were studied. Compared to controls. Cushing's patients had a significant increase (P < 0.001) in the excretion of all principal metabolites of F, secondary to a 5- to 6-fold increase in the cortisol secretion rate [median, 34.0 (range, 13.3-327) mg/day in Cushing's vs. 6.1 (range, 2.5-10.3) mg/day in controls]. The THF plus 5 alpha THF/tetrahydrocortisone ratio was significantly increased in Cushing's syndrome regardless of etiology [mean, 1.81 (range, 1.09-9.99) in Cushing's vs. 0.81 (range, 0.51-1.47) in controls; P < 0.001), indicative of defective 11 beta HSD activity. Furthermore, compared to patients with pituitary-dependent Cushing's, this ratio was significantly higher in patients with the ectopic ACTH syndrome (4.12 vs. 1.49; P < 0.01) and was inversely correlated with serum potassium levels (r = -0.57; P = 0.01; n = 22). One explanation for the mineralocorticoid excess state of the ectopic ACTH syndrome appears to be that cortisol gains inappropriate access to the mineralocorticoid receptor through failure of its normal metabolism by 11 beta HSD. The reason for the defective 11 beta HSD activity is unclear, but it may be secondary to substrate saturation, inhibition by other adrenal steroids, or product inhibition.

Ectopic ACTH secretion due to a bronchopulmonary carcinoid localized by somatostatin receptor scintigraphy

We present the case of a 65-year-old woman with an adrenocorticotropic hormone (ACTH) secreting bronchopulmonary carcinoid. This patient showed the typical long history of Cushing's syndrome, including hypokaliemia, impaired glucose tolerance, high levels of ACTH and beta-endorphin, and coproduction of other peptides. At the onset of clinical symptoms in 1979 an adrenal adenoma was suspected, and left-sided adrenalectomy was performed. The symptoms soon recurred, and the diagnosis of ACTH-dependent Cushing's syndrome was made. As no ACTH-secreting tumor was found, the right adrenal was resected, and the patient was followed up regularly. Fourteen years later chest roentgenography and computed tomography revealed a para-aortic pulmonary lesion, which was suspicious for a bronchopulmonary carcinoid. ACTH and beta-endorphin were excessively, pancreatic polypeptide slightly elevated at that time. The final diagnosis was made using somatostatin receptor scintigraphy which confirmed the hormonal activity of the suspicious lesion; no additional focus was found. This method turned out to be not only a useful additional localization technique but also a promising tool for characterization and staging of a suspected ACTH-producing carcinoid. The tumor was resected curatively, and the diagnosis was confirmed histologically.