Angiotensin II type 1 receptor and ACTH receptor expression in human adrenocortical neoplasms

Primary aldosteronism: molecular medicine meets public health

Primary aldosteronism is the most common single cause of hypertension and is potentially curable when only one adrenal gland is the culprit. The importance of primary aldosteronism to public health derives from its high prevalence but huge under-diagnosis (estimated to be <1% of all affected individuals), despite the consequences of poor blood pressure control by conventional therapy and enhanced cardiovascular risk. This state of affairs is attributable to the fact that the tools used for diagnosis or treatment are still those that originated in the 1970-1990s. Conversely, molecular discoveries have transformed our understanding of adrenal physiology and pathology. Many molecules and processes associated with constant adrenocortical renewal and interzonal metamorphosis also feature in aldosterone-producing adenomas and aldosterone-producing micronodules. The adrenal gland has one of the most significant rates of non-silent somatic mutations, with frequent selection of those driving autonomous aldosterone production, and distinct clinical presentations and outcomes for most genotypes. The disappearance of aldosterone synthesis and cells from most of the adult human zona glomerulosa is the likely driver of the mutational success that causes aldosterone-producing adenomas, but insights into the pathways that lead to constitutive aldosterone production and cell survival may open up opportunities for novel therapies.

The Immunotherapy Landscape in Adrenocortical Cancer

Adrenocortical carcinoma (ACC) is a rare cancer of the adrenal gland that is frequently associated with excess production of adrenal hormones. Although surgical resection may be curative in early-stage disease, few effective therapeutic options exist in the inoperable advanced or metastatic setting. Immunotherapies, inclusive of a broad array of immune-activating and immune-modulating antineoplastic agents, have demonstrated clinical benefit in a wide range of solid and hematologic malignancies. Due to the broad activity across multiple cancer types, there is significant interest in testing these agents in rare tumors, including ACC. Multiple clinical trials evaluating immunotherapies for the treatment of ACC have been conducted, and many more are ongoing or planned. Immunotherapies that have been evaluated in clinical trials for ACC include the immune checkpoint inhibitors pembrolizumab, nivolumab, and avelumab. Other immunotherapies that have been evaluated include the monoclonal antibodies figitumumab and cixutumumab directed against the ACC-expressed insulin-like growth factor 1 (IGF-1) receptor, the recombinant cytotoxin interleukin-13-pseudomonas exotoxin A, and autologous tumor lysate dendritic cell vaccine. These agents have shown modest clinical activity, although nonzero in the case of the immune checkpoint inhibitors. Clinical trials are ongoing to evaluate whether this clinical activity may be augmented through combinations with other immune-acting agents or targeted therapies.

Aldosterone is Aberrantly Regulated by Various Stimuli in a High Proportion of Patients with Primary Aldosteronism

CONTEXT

In primary aldosteronism (PA), aldosterone secretion is relatively independent of the renin-angiotensin system, but can be regulated by several other stimuli.

OBJECTIVE

To evaluate aldosterone response to several stimuli in a series of patients with PA secondary either to bilateral adrenal hyperplasia (BAH) or unilateral aldosterone-producing adenoma (APA).

DESIGN AND SETTING

Prospective cohort study conducted in a university teaching hospital research center.

PATIENTS

Forty-three patients with confirmed PA and subtyped by adrenal vein sampling (n = 39) were studied, including 11 with BAH, 28 with APA, and 4 with undefined etiology. We also studied 4 other patients with aldosterone and cortisol cosecretion.

INTERVENTIONS

We systematically explored aberrant regulation of aldosterone using an in vivo protocol that included the following stimulation tests performed over 3 days under dexamethasone suppression: upright posture, mixed meal, adrenocorticotropin (ACTH) 1-24, gonadotropin-releasing hormone (GnRH), vasopressin, and serotonin R4 agonist.

MAIN OUTCOME MEASURES

Positive response was defined as >50% renin or ACTH-independent increase in plasma aldosterone/cortisol concentration following the various stimulation tests.

RESULTS

Renin-independent aldosterone secretion increased in response to several aberrant stimuli (upright posture, GnRH) in up to 83% of patients with APA or BAH in whom ACTH 1-24 and HT4R agonists also produced aldosterone oversecretion in all patients. The mean significant aberrant responses per patient was similar in BAH (4.6) and in APA (4.0).

CONCLUSIONS

Aldosterone secretion in PA is relatively autonomous from the renin-angiotensin system, but is highly regulated by several other stimuli, which contributes to the large variability of aldosterone levels in PA patients.

Aldosterone-Regulating Receptors and Aldosterone-Driver Somatic Mutations

BACKGROUND

Somatic gene mutations that facilitate inappropriate intracellular calcium entrance have been identified in most aldosterone-producing adenomas (APAs). Studies suggest that angiotensin II and adrenocorticotropic hormone (ACTH) augment aldosterone production from APAs. Little is known, however, regarding possible variations in response to hormonal stimuli between APAs with different aldosterone-driver mutations.

OBJECTIVE

To analyze the transcript expression of type 1 angiotensin II receptors (AGTR1), ACTH receptors (MC2R), and melanocortin 2 receptor accessory protein (MRAP) in APAs with known aldosterone-driver somatic mutations.

METHODS

RNA was isolated from APAs with mutations in: KCNJ5 (n = 14), ATP1A1 (n = 14), CACNA1D (n = 14), and ATP2B3 (n = 5), and from normal adjacent adrenal tissue (n = 45). Transcript expression of MC2R, MRAP, AGTR1, aldosterone synthase (CYP11B2), 17α-hydroxylase/17,20-lyase (CYP17A1), and 11β-hydroxylase (CYP11B1) were quantified using quantitative RT-PCR and normalized to β-actin.

RESULTS

Compared to adjacent normal adrenal tissue, APAs had higher transcript levels of CYP11B2 (2,216.4 [1,112.0, 2,813.5]-fold, p < 0.001), MC2R (2.88 [2.00, 4.52]-fold, p < 0.001), and AGTR1 (1.80 [1.02, 2.80]-fold, p < 0.001]), and lower transcript levels of MRAP, CYP17A1, and CYP11B1 (0.28-0.36, p < 0.001 for all). MC2R and CYP11B2 transcripts were lower in APAs with KCNJ5 vs. other mutations (p < 0.01 for both). MC2R expression correlated positively with that of AGTR1 in APAs harboring KCNJ5 and CACNA1D mutations, and with MRAP expression in APAs harboring ATPase mutations.

CONCLUSIONS

While MC2R and AGTR1 are expressed in all APAs, differences were observed based on the underlying aldosterone-driver somatic mutations. In tandem, our findings suggest that APAs with ATPase-mutations are more responsive to ACTH than KCNJ5-mutated APAs.

Suppressed ACTH Is Frequently Unrelated to Autonomous Cortisol Secretion in Patients With Adrenal Incidentalomas

OBJECTIVE

ACTH is considered a weak marker for autonomous cortisol secretion (ACS) in patients with adrenal incidentalomas (AIs). Our aim was to investigate suppressed basal ACTH as a marker of ACS and to elucidate why this criterion is of limited value.

METHODS

Basal ACTH and cortisol after overnight dexamethasone suppression test (cortisolONDST) were measured in 198 patients with unilateral AI and at 2-year follow-up. Basal ACTH was measured in 100 control subjects.

RESULTS

In patients with cortisolONDST <50 nmol/L (n = 145), ACTH was <2 pmol/L in 19%, compared with 4% in control subjects (P < 0.001). ACTH and size of AI correlated negatively (P = 0.002). Among patients with cortisolONDST ≥50 nmol/L, ACTH was <2 pmol/L in 53%. The patients were grouped according to whether cortisolONDST was <50 or ≥50 nmol/L and whether ACTH was <2.0 or ≥2.0 or pmol/L. At follow-up, these four groups were still separated with statistically significant differences in ACTH and cortisolONDST.

CONCLUSIONS

This study identifies a previously unrecognized group of patients defined by suppressed ACTH despite normal cortisolONDST. This suppression of ACTH by a factor other than ACS may explain the limitation of suppressed ACTH as a marker for ACS. We suggest increased cortisol secretion in response to ACTH by the AI to be an additional factor.

Subtype prediction in primary aldosteronism: measurement of circadian variation of adrenocortical hormones and 24-h urinary aldosterone

OBJECTIVE

Currently, adrenal venous sampling (AVS) is the only reliable method to distinguish unilateral from bilateral hyperaldosteronism in primary aldosteronism (PA). However, AVS is costly and time-consuming compared with simple blood tests. In this study, we conducted a retrospective study to determine whether circadian variation in plasma adrenocortical hormone levels (i.e. aldosterone, cortisol and ACTH) and a 24-h urinary aldosterone could contribute to the clinical differentiation between unilateral hyperaldosteronism (UHA) and bilateral hyperaldosteronism (BHA).

DESIGN

In 64 patients who were diagnosed with PA and underwent AVS, 32 and 22 patients were diagnosed with UHA and BHA, respectively. Plasma adrenocortical hormone levels at 0:00, 6:00, 12:00 and 18:00 and 24-h urinary aldosterone under a condition of 6 g daily dietary sodium chloride intake were measured.

RESULTS

Baseline plasma aldosterone concentration (PAC) and 24-h urinary aldosterone level in patients with UHA were significantly higher than in patients with BHA, particularly at 6:00. The area under the ROC curve for PAC at 0:00, 6:00, 12:00 and 18:00 and 24-h urinary aldosterone to discriminate UHA and BHA was 0·839 [95% confidence interval (CI); 0·73-0·95], 0·922 (95% CI; 0·85-1·00), 0·875 (95% CI; 0·78-0·97), 0·811 (95% CI; 0·69-0·93), 0·898 (95% CI; 0·81-0·99), respectively.

CONCLUSIONS

PAC at different blood sampling times and 24-h urinary aldosterone level may be diagnostically helpful in discriminating between UHA and BHA. We believe that these tests could reduce the number of unnecessary AVS procedures.

Role of ACTH and Other Hormones in the Regulation of Aldosterone Production in Primary Aldosteronism

The major physiological regulators of aldosterone production from the adrenal zona glomerulosa are potassium and angiotensin II; other acute regulators include adrenocorticotropic hormone (ACTH) and serotonin. Their interactions with G-protein coupled hormone receptors activate cAMP/PKA pathway thereby regulating intracellular calcium flux and CYP11B2 transcription, which is the specific steroidogenic enzyme of aldosterone synthesis. In primary aldosteronism (PA), the increased production of aldosterone and resultant relative hypervolemia inhibits the renin and angiotensin system; aldosterone secretion is mostly independent from the suppressed renin-angiotensin system, but is not autonomous, as it is regulated by a diversity of other ligands of various eutopic or ectopic receptors, in addition to activation of calcium flux resulting from mutations of various ion channels. Among the abnormalities in various hormone receptors, an overexpression of the melanocortin type 2 receptor (MC2R) could be responsible for aldosterone hypersecretion in aldosteronomas. An exaggerated increase in plasma aldosterone concentration (PAC) is found in patients with PA secondary either to unilateral aldosteronomas or bilateral adrenal hyperplasia (BAH) following acute ACTH administration compared to normal individuals. A diurnal increase in PAC in early morning and its suppression by dexamethasone confirms the increased role of endogenous ACTH as an important aldosterone secretagogue in PA. Screening using a combination of dexamethasone and fludrocortisone test reveals a higher prevalence of PA in hypertensive populations compared to the aldosterone to renin ratio. The variable level of MC2R overexpression in each aldosteronomas or in the adjacent zona glomerulosa hyperplasia may explain the inconsistent results of adrenal vein sampling between basal levels and post ACTH administration in the determination of source of aldosterone excess. In the rare cases of glucocorticoid remediable aldosteronism, a chimeric CYP11B2 becomes regulated by ACTH activating its chimeric CYP11B1 promoter of aldosterone synthase in bilateral adrenal fasciculate-like hyperplasia. This review will focus on the role of ACTH on excess aldosterone secretion in PA with particular focus on the aberrant expression of MC2R in comparison with other aberrant ligands and their GPCRs in this frequent pathology.

Multiple aberrant hormone receptors in Cushing's syndrome

The mechanisms regulating cortisol production when ACTH of pituitary origin is suppressed in primary adrenal causes of Cushing's syndrome (CS) include diverse genetic and molecular mechanisms. These can lead either to constitutive activation of the cAMP system and steroidogenesis or to its regulation exerted by the aberrant adrenal expression of several hormone receptors, particularly G-protein coupled hormone receptors (GPCR) and their ligands. Screening for aberrant expression of GPCR in bilateral macronodular adrenal hyperplasia (BMAH) and unilateral adrenal tumors of patients with overt or subclinical CS demonstrates the frequent co-expression of several receptors. Aberrant hormone receptors can also exert their activity by regulating the paracrine secretion of ACTH or other ligands for those receptors in BMAH or unilateral tumors. The aberrant expression of hormone receptors is not limited to adrenal CS but can be implicated in other endocrine tumors including primary aldosteronism and Cushing's disease. Targeted therapies to block the aberrant receptors or their ligands could become useful in the future.

Dissecting the molecular pathways of primary aldosteronism

The great majority of the cases clinically diagnosed as primary aldosteronism (PA) have been caused by aldosterone-producing adenoma (APA) or idiopathic hyperaldosteronism (IHA). The differential diagnosis of both subtypes of PA is important due to the different therapeutic modes but clinically it is sometimes difficult. It is also important to understand the morphological features of these two subtypes with special emphasis upon differences of the status for aldosterone biosynthesis. In the last decade, molecular mechanisms of PA including the aberrant expression of G-protein coupled receptors (GPCRs), key regulators of the intracellular calcium signaling pathway and somatic mutations of ion channels, have been revealed and our understanding of the molecular pathways involved in excessive aldosterone production has been markedly advanced. In addition, newly developed monoclonal antibodies specific to the isoform of adrenal steroidogenic enzymes have demonstrated the novel profiles of adrenal steroidogenesis in PA. These novel findings indicate that the molecular mechanisms on the onset and pathophysiology of PA are more complicated than previously considered and further clarification of clinical relevance of these findings is required at this juncture.

Association of polymorphisms in AGTR1 and AGTR2 genes with primary aldosteronism in the Chinese Han population

HYPOTHESIS

Polymorphisms in angiotensin II type-1/2 receptor genes (AGTR1/AGTR2) may be involved in the pathogenesis of primary aldosteronism. The present study aims to reveal some loci susceptible to the disease on the genes in a group of Chinese Han nationality.

MATERIALS AND METHODS

A case-control study was conducted in 202 patients and 188 controls. Ten tagging SNPs on AGTR1/AGTR2 were genotyped for all subjects via the method of multiplex PCR-ligase detection reaction. Statistical analysis was performed with chi-square test and logistic regression analysis.

RESULTS

rs3772616 on the AGTR1 gene was a factor for susceptibility to primary aldosteronism (p<0.001), and the TT genotype significantly decreased the risk of primary aldosteronism compared with the CC homozygote (p=0.008, adjusted OR=0.13; 95%CI: 0.03-0.59). The rs3772616 polymorphism was associated with primary aldosteronism under the additive and dominant models. The female carriers of the G allele in rs5193 showed a significant difference compared with the T allele.

CONCLUSIONS

The AGTR1 rs3772616 polymorphism can be considered as a hereditary marker for primary aldosteronism, and in the Chinese Han population the rs5193 G allele seems to predispose to it only in women.

Cortisol secretion from adrenal adenomas discovered as incidentalomas is responsive to ACTH

OBJECTIVE

Adrenal adenomas discovered as incidentalomas may secrete cortisol and cause subclinical hypercortisolism. This cortisol secretion is considered to be autonomous. The aim was to investigate whether cortisol secretion by adenomas is responsive to ACTH.

DESIGN

Descriptive retrospective study of consecutive patients.

PATIENTS

Eighty patients found to have adrenal incidentalomas during 2008 and 2009 at our hospital were examined, and 50 patients with a unilateral adenoma were included in the study.

MEASUREMENTS

Cortisol and ACTH were measured at baseline and using 1-mg overnight dexamethasone suppression test (DST). The cortisol response to ACTH was calculated using the expression: (cortisolbasal -cortisolDST )/(ACTHbasal -ACTHDST ).

RESULTS

The patients were divided into three groups according to their basal ACTH: ≥3·0 pm (29 patients), 2·0-2·9 pm (9 patients) and <2·0 pm (12 patients). Cortisol at DST was similar in the three groups: 30, 46 and 43 nm (P = 0·10). The cortisol response to ACTH increased stepwise between the groups: 98, 172 and 249 nm/pm (P = 0·000, undetectable ACTH was set to 0 pm). Basal ACTH was negatively correlated with the size of the adenoma and positively correlated with the attenuation of the adenoma at unenhanced CT (P = 0·03 and P = 0·04, respectively).

CONCLUSIONS

Patients with adrenal adenomas and low basal ACTH show increased cortisol response to ACTH, and the adenomas seem to be the source of the increased cortisol secretion. The increased response to ACTH could be a pathogenic factor in metabolic complications of subclinical hypercortisolism. The cortisol response to ACTH may therefore be a useful measure of subclinical hypercortisolism.

Protein kinase C-induced activin A switches adrenocortical steroidogenesis to aldosterone by suppressing CYP17A1 expression

Functional zonation of the adrenal cortex is a consequence of the zone-specific expression of P450c17 (CYP17A1) and its cofactors. Activin and inhibin peptides are differentially produced within the zones of the adrenal cortex and have been implicated in steroidogenic control. In this study, we investigated whether activin and inhibin can function as intermediates in functional zonation of the human adrenal cortex. Activin A suppressed CYP17A1 expression and P450c17 function in adrenocortical cell lines as well as in primary adrenal cell cultures. Inhibin βA-subunit mRNA and activin A protein levels were found to be increased up to 1,900-fold and 49-fold, respectively, after protein kinase C (PKC) stimulation through PMA or angiotensin II in H295R adrenocortical carcinoma cells. This was confirmed in HAC15 cells and for PMA in primary adrenal cell cultures. Both PMA and Ang II decreased CYP17A1 expression in the adrenocortical cell lines, whereas PMA concurrently suppressed CYP17A1 levels in the primary cultures. Inhibition of activin signaling during PKC stimulation through silencing of the inhibin βA-subunit or blocking of the activin type I receptor opposed the PMA-induced downregulation of CYP17A1 expression and P450c17 function. In contrast, PKA stimulation through adrenocorticotrophin or forskolin increased expression of the inhibin α-subunit and betaglycan, both of which are antagonists of activin action. These data indicate that activin A acts as a PKC-induced paracrine factor involved in the suppression of CYP17A1 in the zona glomerulosa and can thereby contribute to functional adrenocortical zonation.

Inhibins and activins: their roles in the adrenal gland and the development of adrenocortical tumors

The adrenal gland is composed of two separate endocrine tissues that control a multitude of bodily functions in their adaptation to external and internal stressors through hormone secretion. The functions of the adrenal gland are regulated by circulating, neural and local factors that ensure proper cell growth and hormone production. Activins and inhibins are among the locally expressed growth factors affecting adrenal cell function. They have been found to influence several aspects of adrenal cell development, adrenocortical steroidogenesis, adrenocortical tumor formation and adrenomedullary cell differentiation. Especially the finding that inhibin α-subunit knockout mice develop adrenocortical carcinomas after gonadectomy has prompted research on the physiological and pathophysiological roles of activin and inhibin in the adrenal cortex. It is now clear that both peptides control adrenocortical physiology and are involved in adrenocortical tumorigenesis at multiple levels, both in murine models as well as in human patients.

Screening for membrane hormone receptor expression in primary aldosteronism

OBJECTIVE

The investigation of expression and functional relevance of G-protein coupled receptors in primary aldosteronism (PA) by molecular and clinical studies.

PATIENTS AND METHODS

Tissues of 14 aldosterone-producing adenomas (APA), of one unilateral adrenal hyperplasia and of six healthy adult adrenal glands; 12 patients with confirmed PA due to APA; (n=5), idiopathic hyperaldosteronism (n=7) and 8 control subjects (C). The tissues were subjected to a quantitative PCR for determination of mRNA expression levels of AT2R1, GIPR, MC2R, GnRHR, LHR, TRHR, TSHR, glucagon-R, V1aR, V2R, and 5-HT4R. The patients and controls were enrolled in a test protocol consisting of stimulation by posture, mixed meal, ACTH, GnRH, TRH, glucagon, vasopressin, and metoclopramide (MCP). Three patients could be analyzed by both studies. A positive response was defined as an aldosterone increase of more than 50% following stimulation.

RESULTS

All the tissues revealed AT2R1, MC2R, AVPR, and 5-HT4R mRNA expression. LHR mRNA was found in normal adrenals and 13 adrenal tumors. By contrast with normal adrenals tumorous adrenal tissue expressed GnRHR mRNA (4/15) and TSHR mRNA (1/15). Both the patients and controls responded to posture, ACTH, glucagon, AVP, and MCP. Specific responses were seen in one patient following TRH and three patients following GnRH stimulation.

CONCLUSIONS

We provide evidence for peptide hormone responsiveness to various peptide hormones in patients with PA, including GnRH and TRH. A good correlation between clinical and molecular testing could be observed, making an involvement of the receptor expressed in PA possible.

Discerning malignancy in resected adrenocotical tumors

BACKGROUND

The number of adrenocortical tumors discovered incidentally has recently increased owing to the advent of imaging techniques. The most important diagnostic point in evaluation of resected specimens of these tumors is to discern malignancy to determine postoperative management of the patients.

OBJECTIVE/METHODS

To determine what the effective methods of discerning malignancy in resected specimens of adrenocortical tumors are at this juncture. To provide relevant and practical information pertinent to those involved in the management of patients with adrenocortical tumors.

CONCLUSION

Careful macroscopic evaluation, including the selection of the specimens submitted and application of the criteria of Weiss for histological diagnosis, is still considered the 'gold standard' for diagnosis of adrenocortical carcinoma. However, it is important to recognize its limitations in the diagnosis of adrenocortical oncocytoma and pediatric adrenocortical tumors. The auxiliary methods that may be of clinical relevance at this juncture include the analysis of the Ki67/MIB-1 labeling index and IGF-II expression in the tumors.

Immunohistochemical detection of angiotensin receptors AT1 and AT2 in adrenal tumors

Angiotensin II is well known to affect the adrenal cell growth and function. Angiotensin receptors AT1 and AT2 were found to be present in the normal adrenal gland. However, the data on the expression of the angiotensin receptors in the adrenal tumors are very scarce. To overcome this gap, the paraffin sections of the adrenal cortical tumors and of pheochromocytomas from the archival material were immunostained with antibodies raised against AT1 (sc-1173) and AT2 (sc-9040) receptor proteins. In hyperplasia of the adrenal cortex and in benign adrenocortical adenomas, both functioning and non-functioning, the AT1 immunostaining was present mainly in the cell membranes. A positive immunoreaction was also found in the subpopulation of cell nuclei and within the cytoplasm. In the adrenal cancer, as well as in pheochromocytomas, neither cell membranes nor cell nuclei were immunostained with anti-AT1 antibody. However, a weak AT1 immunostaining was present within the cytoplasm of tumoral cells. With anti-AT2 antibody, in all tumors investigated, the tumoral cells were immunonegative but moderate to strong AT2 immunostaining was observed in the walls of intratumoral blood vessels and in the interstitial tissue. Our data indicates that the expression of AT1 receptors is altered in adrenal cancer and in pheochromocytomas. The expression of AT2 receptors, in turn, may be connected with the process of tumoral neo-angiogenesis.

Angiotensin II stimulates the reactivity of the pituitary-adrenal axis in leptin-resistant Zucker rats, thereby influencing the glucose utilization

The HPA axis is hyperactive under conditions of leptin and insulin resistance as well as after ANG II administration. We hypothesized that a hyperreactivity of the HPA axis to ANG contributes to an impaired glucose utilization in obesity, since leptin resistance and an overactive renin-angiotensin-aldosterone system are features of obesity. Zucker rats were treated with ANG via subcutaneous minipumps (0, 0.9, and 9.0 mug/h; 4 wk). PA axis reactivity and glucose homeostasis were characterized after CRH treatment and during an oral glucose tolerance test (OGTT). The elevated plasma profile of corticosterone after CRH stimulation in saline-treated OZR compared with LZR confirmed that the sensitization of the PA axis depended on leptin resistance. Irrespective of the rat strain, circulating ANG levels and blood pressure were selectively increased after administration of 9 mug/h ANG (high ANG). Only high ANG induced an elevation of the corticosterone and glucose response after CRH stimulation in OZR but did not affect the ACTH secretion. During OGTT, corticosterone and consequently glucose increased in OZR after high ANG, whereas the insulin secretion was decreased. In the adrenal glands of OZR, AT(1A) receptor mRNA levels increased after high ANG. We conclude that the impairment of glucose utilization after ANG stimulation is potentiated in leptin-resistant rats as a result of a hyperreactive PA axis, thereby confirming the functional importance of a dysregulation within the HPA axis in metabolic syndrome or obesity. The ACTH-independent stimulation of corticosterone release and the selective increase of AT(1A) receptor mRNA in the adrenals of OZR indicated a sensitization of adrenals toward ANG, causing a stimulation of the PA axis.

Primary hyperaldosteronism is associated with derangement in the regulation of the hypothalamus-pituitary-adrenal axis in humans

Hippocampal mineralocorticoid receptors (MR) play a major role in the control of hypothalamus- pituitary-adrenal (HPA) axis. The functional profile of HPA axis and the impact of MR blockade under chronic exposure to mineralocorticoid excess are unknown. To clarify this issue, ACT H, cortisol, and aldosterone secretions were studied in 6 patients with primary hyperaldosteronism (HA) and 8 controls (NS) during placebo, placebo+human CR H (hCR H) (2 microg/kg iv bolus at 22:00 h), potassium canrenoate (CAN, 200 mg iv bolus at 20:00 h followed by 200 mg infused over 4 h) or CAN+hCR H. During placebo, both aldosterone and ACT H levels were higher (p<0.01) in HA than in NS, while cortisol levels were not significantly different. Both HA and NS showed significant ACT H and cortisol responses to hCR H (p<0.004), although the hormonal responses in HA were higher (p<0.02) than in NS. CAN infusion did not modify aldosterone levels in both HA and NS. Under CAN infusion, ACT H showed progressive rise in NS (p<0.05) but not in HA, while cortisol levels showed a significant (p<0.05) but less marked and delayed increase in HA compared to NS. CAN enhanced hCRH-induced ACTH and cortisol responses in NS (p<0.05), but not in HA. In conclusion, in humans primary hyperaldosteronism is associated with deranged function of the HPA axis. In fact, hyperaldosteronemic patients show basal and hCR H-stimulated HPA hyperactivity that is, at least partially, refractory to further stimulation by mineralocorticoid blockade with canrenoate. Whether this hormonal alteration can influence the clinical feature of hypertensive patients with primary hyperaldosteronism needs to be clarified.

PET Imaging of the AT1 receptor with [11C]KR31173

AIM

The goal of this study was to investigate the binding characteristics of [(11)C]KR31173 and its applicability for PET studies of the AT(1) receptor (AT(1)R).

METHODS

Ex vivo biodistribution and pharmacology were tested in mice. PET imaging was performed in mice, beagle dogs and a baboon. To assess nonspecific binding, PET imaging was performed both before and after pretreatment with a potent AT(1)R antagonist. In the baboon, PET imaging was also performed with the previously developed radioligand [(11)C]L-159,884 for comparison.

RESULTS

Ex vivo biodistribution studies in mice showed specific binding rates of 80-90% in the adrenals, kidneys, lungs and heart. Specific binding was confirmed in mice using small animal PET. In dogs, renal cortex tissue concentration at 75-95 min postinjection (pi) was 63 nCi/ml per millicurie at a specific binding rate of 95%. In the baboon renal cortex, tissue activity at 55-75 min pi was 345 nCi/ml per millicurie. In the baboon the specific binding of [(11)C]KR31173 was higher (81%) than the specific binding of [(11)C]L-159,884 (34%).

CONCLUSION

[(11)C]KR31173 shows accumulation and significant specific binding to the AT(1)R in the kidneys of mice, dogs and baboon. These findings suggest that this radioligand is suited for imaging the renal cortical AT(1)R in multiple species.

Steroidogenesis in aldosterone-producing adenoma revisited by transcriptome analysis

CONTEXT

Primary aldosteronism (PAL) is the most frequent cause of secondary arterial hypertension. In PAL, aldosterone production is chronic, excessive, and autonomous.

OBJECTIVE

The objective of this study was to identify the angiotensin-II independent alterations of steroidogenesis responsible for PAL.

DESIGN

Genomewide gene expression was compared in two tissues differentiated for aldosterone production, both nonstimulated by circulating angiotensin II and differing in their autonomy to produce aldosterone: aldosterone-producing adenoma (APA) and its adjacent dissected zona glomerulosa (ZG).

SETTING

The setting of this study was the Comete Network.

PATIENTS

Patients with APA were studied.

INTERVENTION

Transcriptome comparison was made of one APA and its adjacent ZG by serial analysis of gene expression; validation by in situ hybridization was performed for 19 genes in 11 samples.

OUTCOME

The study outcome was genes differentially expressed in APA and adjacent ZG.

RESULTS

Activation of steroidogenesis in PAL is restricted to the overexpression of the enzymes producing aldosterone-specific steroids, aldosterone synthase and also 21-hydroxylase, suggesting that upstream precursor production is not limiting. Increased expression of high-density lipoprotein receptor, adrenodoxin and P450 oxidoreductase suggests that these systems provide cholesterol and electrons to the mitochondrial steroidogenic enzymes. As for acute stimulation of aldosterone production, an activation of calcium signaling is suggested by concordant overexpression of calcium-binding proteins or effectors. Calcium activation may result from an abnormal activity of G(q) protein-coupled receptors. This calcium activation may be the starting point of the other gene expression changes observed in APA. Finally, other differentially expressed genes include three genes encoding unidentified proteins.

CONCLUSION

This work provides an original and integrated view of the mechanisms of aldosterone production in PAL.

Steroidogenic acute regulatory (StAR)-directed immunotherapy protects against tumor growth of StAR-expressing Sp2-0 cells in a rodent adrenocortical carcinoma model

Adrenocortical carcinoma (ACC) is a highly malignant tumor with poor response to classical antitumor therapy. Steroidogenic acute regulatory (StAR) protein is expressed in most human ACCs. The aim of this study was to induce antitumoral T cells directed against StAR in a murine tumor model. Because a suitable syngenic adrenocortical mouse tumor model is lacking, we established a clone of the mouse myeloma Sp2-0 tumor cell line stably expressing murine StAR (Sp2-mStAR). Using repeated im injections of plasmid DNA encoding mStAR followed by infection with a recombinant vaccinia virus (rVV) expressing mStAR, we induced a cytotoxic T-cell response as measured by enzyme-linked immunospot assay. To demonstrate antitumor activity of the vaccination procedure, mice were treated as follows: group A, mice immunized with plasmids and rVV encoding mStAR receiving Sp2-mStAR cells; control group B, mice immunized with the empty plasmid and the empty rVV receiving Sp2-mStAR cells; control group C, mice immunized with the empty plasmid and rVV encoding P450 side-chain cleavage enzyme receiving Sp2-mStAR cells; and control group D, mice immunized with plasmid and rVV encoding mStAR receiving parental Sp2-0 cells. A high proportion (89-100%) of the control groups B, C, and D developed subcutaneous tumors. In contrast, immunization specific for mStAR (group A) was highly protective against tumor growth (percentage of tumor-free animals, 67%; P < 0.001 vs. controls). In summary, these results show that T-cell tolerance toward mStAR can be broken, resulting in antitumoral immunity. Thus, StAR represents a candidate target antigen for immunotherapeutic strategies against ACC.

The molecular pathogenesis of hereditary and sporadic adrenocortical and adrenomedullary tumors

Modern imaging modalities lead to frequent detection of adrenal masses, most of them incidental findings. Although the majority of adrenocortical and adrenomedullary tumors are benign, there are no reliable clinical and laboratory markers to distinguish most of them from malignant neoplasms. The molecular mechanisms underlying the pathogenesis of these tumors have recently begun to be unraveled. A fruitful avenue for the elucidation of tumorigenesis has been the study of adrenal tumors that are manifestations of hereditary or postzygotic genetic syndromes, because one knows the "first hit", i.e. the primary gene defect. In contrast, in sporadic adrenal tumors the first hit, possibly a somatic mutation of a tumor-related gene, is unknown, and therefore the sequence of genetic alterations is difficult to establish. In this article we review in addition to our own work the literature on molecular aspects of adrenocortical and adrenomedullary tumorigenesis.