Cellular and molecular abnormalities of a macronodular adrenal hyperplasia causing beta-blocker-sensitive Cushing's syndrome

Abstract

Cushing's syndrome due to ACTH-independent macronodular adrenal hyperplasia (AIMAH) can be associated with abnormal responses of aberrantly expressed adrenocortical receptors. This study aimed to characterize in vitro the pathophysiology of hypercortisolism in a β-blocker-sensitive Cushing's syndrome due to AIMAH. Cortisol secretion profile under aberrant receptors stimulation revealed hyperresponsiveness to salbutamol (β2-adrenoceptor agonist), cisapride (5-HT4 receptor agonist), and vasopressin in AIMAH cultured cells, but not in normal adrenocortical cells. By RT-PCR, AIMAH tissues revealed β2-adrenoceptor overexpression rather than ectopical expression. MC2R expression was similar in both AIMAH and normal adrenocortical tissues. Curiously, cortisol levels of AIMAH cells under basal condition were 15-fold higher than those of control cells and were not responsive to ACTH. Analysis of culture medium from AIMAH cells could detect the presence of ACTH, which was immunohistochemically confirmed. Finally, the present study of AIMAH cells has identified: a) cortisol hyperresponsiveness to catecholamines, 5-HT4 and vasopressin in vitro, in agreement with clinical screening tests; b) abnormal expression of β2-adrenoceptors in some areas of the hyperplastic adrenal tissue; c) autocrine loop of ACTH production. Altogether, the demonstration of aberrant responses to hormonal receptors and autocrine hormone production in the same tissue supports the assumption of multiple molecular alterations in adrenal macronodular hyperplasia. A síndrome de Cushing secundária à hiperplasia adrenal macronodular independente de ACTH (AIMAH) pode estar associada com respostas anômalas a estímulos sobre receptores hormonais expressos de maneira aberrante no córtex adrenal. O objetivo deste trabalho foi caracterizar a fisiopatologia do hipercortisolismo in vitro na sín-drome de Cushing responsiva a β-bloqueadores decorrente de AIMAH. Em cultura de células, a secreção de cortisol apresentou resposta aumentada ao salbutamol (agonista β2-adrenérgico), à cisaprida (agonista de receptor 5-HT4) e à vasopressina, na AIMAH mas não no córtex adrenal normal. O estudo de receptores aberrantes por RT-PCR demonstrou que o gene do receptor β2-adrenérgico estava superexpresso (e não expresso ectopicamente) nos fragmentos da AIMAH quando comparado ao tecido normal. A expressão de MC2R foi semelhante em ambos. Curiosamente, o nível basal de secreção de cortisol pelas células da AIMAH foi 15 vezes superior às células normais, não havendo resposta das células AIMAH ao estímulo com ACTH. A análise do meio de cultura das células AIMAH revelou a presença de ACTH, que foi confirmada por estudo imuno-histoquímico. Em suma, este estudo demonstrou: a) aumento dos níveis de cortisol in vitro em resposta a catecolaminas, 5-HT4 e vasopressina, correspondendo aos resultados dos testes clínicos para pesquisa de receptores aberrantes; b) expressão anormal de receptores β2-adrenérgicos em algumas áreas de hiperplasia; c) produção autócrina de ACTH. Estes resultado...

ACTH-Independent Hypercorticism in Adrenal Tumors and Adrenocortical Hyperplasia

“…43,60 Administration of AVP to some patients with Cushing's syndrome increases the plasma cortisol concentration without changing the corticotropin concentration. [36][37][38][39][40]46 The same effect was observed with lysine-8-vasopressin, 61 but not with desmopressin (DDAVP, a synthetic V2 receptor agonist alternative for vasopressin). [36][37][38][39][40] Cortisol secretion stimulated by AVP was suppressed by oral administration of SR 49059 38 or OPC-21268, 62 both V1-vasopressin-receptor antagonists, only with patients in a horizontal, supine position.…”

“…41 All 5-HT receptors except 5-HT 3 are G-protein coupled receptors (GPCRs), and most of them are coupled with adenylyl cyclase. Both 5-HT and cisapride, a 5-HT 4 receptor agonist, stimulated cortisol production in vivo, 42 in cultured cells from adrenal hyperplasia 37,43,44 and adrenocortical carcinoma. 45 Patients with Cushing's syndrome treated with 5-HT 4 receptor agonists cisapride, 43,46-50 metoclopramide, 46,48 and zacopride demonstrated increased cortisol levels.…”

“…33 Beta-2 adrenergic receptors were identified in human adrenocortical cortisol-producing adenomas 34,35 or hyperplasia. [36][37][38] Cell cultures from AIMAH showed hyperresponsiveness to isoproterenol, a nonselective beta-adrenergic receptor agonist, and salbutamol, a beta-2 adrenergic receptor agonist. 37 Propranolol, a beta-adrenergic antagonist usually used to treat hypertension and heart dysrhythmias, greatly decreased the patient's urinary cortisol excretion.…”

“…[36][37][38] Cell cultures from AIMAH showed hyperresponsiveness to isoproterenol, a nonselective beta-adrenergic receptor agonist, and salbutamol, a beta-2 adrenergic receptor agonist. 37 Propranolol, a beta-adrenergic antagonist usually used to treat hypertension and heart dysrhythmias, greatly decreased the patient's urinary cortisol excretion. 37,38 Meanwhile, treatment with isoproterenol, a beta-adrenergic agonist usually used to treat bradycardia and heart block, stimulated cortisol production.…”

“…37 Propranolol, a beta-adrenergic antagonist usually used to treat hypertension and heart dysrhythmias, greatly decreased the patient's urinary cortisol excretion. 37,38 Meanwhile, treatment with isoproterenol, a beta-adrenergic agonist usually used to treat bradycardia and heart block, stimulated cortisol production. 39 Incubation of cultured cells expressing the beta-adrenergic receptors with the peptide hormone AVP and epinephrine together induced a stronger cortisol response than the individual agents alone.…”