BIOCHEMICAL, HISTOPATHOLOGICAL, AND GENETIC CHARACTERIZATION OF POSTURE RESPONSIVE AND UNRESPONSIVE ALDOSTERONE-PRODUCING ADENOMAS

Abstract

Objective: Aldosterone-producing adenoma (APA) accounts for ∼30% of primary aldosteronism. Based on responses of aldosterone to upright posture, APA can be divided into posture-responsive and –unresponsive forms. Somatic gene mutations in KCNJ5, CACNA1D, ATP1A1, or ATP2B3 have been reported to exist in more than 90% of APAs. We sought to compare the biochemical, histopathological, and genetic characterization between these two types of APAs. Design and method: Posture-responsive was defined as showing a rise in plasma aldosterone concentration of at least 50% 2 - 3 h after the assumption of upright posture (10 AM) above the basal level (7 AM) following overnight recumbency. Plasma levels of aldosterone and hybrid steroids (18-oxocortisol and 18-hydroxycortisol) were measured by LC-MS/MS. Histologic analysis and immunohistochemistry for CYP11B2 (aldosterone synthase) and CYP17A1 (17aplha-hydroxylase) were performed on APA tissue sections collected from 24 posture-unresponsive and 17 posture-responsive APA patients. Sanger sequencing of KCNJ5 and gene targeted next-generation sequencing were performed to detect somatic gene mutations. Results: Compared to patients with posture-responsive APA (of which 48.7% were composed of zona glomerulosa (ZG)-like cells and 35.3% showed ZG-zona fasciculata (ZF) mixed appearance), posture-unresponsive APA patients displayed higher (P < 0.01) levels of hybrid steroids, recumbent aldosterone and cortisol, greater (P < 0.05) suppression of aldosterone secretion from the contralateral unaffected adrenal, and larger (P < 0.01) tumors mostly composed of ZF-like cells that had higher (P < 0.01) expression of CYP17A1 (but not of CYP11B2). Of 41 studied APAs, 37 (90.2%) harboured aldosterone-driving somatic mutations (KCNJ5 = 14, 34.1%; CACNA1D = 13, 31.7%; ATP1A1 = 8, 19.5%; and ATP2B3 = 2, 4.9%), including 5 that were previously unreported (3 in CACNA1D and 2 in ATP1A1). Interestingly, 64.7% (11/17) of posture-responsive APAs carried CACNA1D mutations, whereas 54.2% (13/24) of posture-unresponsive APAs harboured KCNJ5 mutations. Conclusions: The excessive production of hybrid steroids by posture-unresponsive APAs may relate to their ZF-like tumor cell composition, resulting in strong expression of CYP17A1 (in addition to somatic gene mutation-driven CYP11B2 expression), thereby allowing production of cortisol which acts as the substrate for CYP11B2-generated hybrid steroids.