ACE2 AND ANGIOTENSIN-(1-7) AND ALDOSTERONE BIOSYNTHESIS IN HUMAN ADRENOCORTICAL TISSUES

Abstract

Objective: The angiotensin converting enzyme 2 (ACE2) and its product angiotensin-(1–7) (Ang-(1–7)) were suggested to play cardiovascular protective effects via angiotensin type 2 (AT2R), MasR and alamandine receptors. Whether this involves blunting of aldosterone biosynthesis in humans remains unknown. Design and method: We quantified ACE2 mRNA in human aldosterone-producing adenoma (APA) and APA-adjacent tissue obtained ex vivo from primary aldosteronism (PA) patients with real-time and ddPCR. We also investigated the effects of Ang-(1–7) and diminazene aceturate (DIZE), a putative ACE2 activator, on aldosterone synthase (CYP11B2) and 11b-hydroxylase (CYP11B1) as proxy for aldosterone and cortisol secretion, respectively, in the absence and presence of the AT1R antagonist irbesartan, or the MasR antagonist A779. Results: We detected ACE2 mRNA at higher amounts in APA-adjacent tissue than in APA. Functional in vitro studies with LC-MS showed active conversion of Ang II into Ang 1–7, albeit at low level, through ACE-2-independent mechanisms. At [10–8 M] Ang-(1–7) did not affect CYP11B1 and CYP11B2 gene transcripts, while at high concentration [10–6 M] it increased both mRNAs (p < 0.001 vs vehicle) through an AT1-R-mediated mechanism as these stimulatory effects were abolished by irbesartan. To investigate if Ang-(1–7) could blunt aldosterone production when CYP11B2 is upregulated, we exposed H295 cells to [10–8 M] Ang II and found that Ang-(1–7) did not blunt Ang II-induced expression of CYP11B1 and CYP11B2 mRNA. Moreover, we discovered that [10–7 M] DIZE increased ACE2 mRNA by 1.5 fold from baseline (p = 0.01) but left CYP11B1 or CYP11B2 mRNA levels unaffected. DIZE did not blunt the AT1R mediated stimulatory effect of [10–6 M] Ang-(1–7) on CYP11B1 and CYP11B2 mRNA. Conclusions: Thus, although Ang-(1–7) can be locally generated at low levels and MasR and ACE2 mRNAs are detectable in APA and APA-adjacent tissue, neither Ang-(1–7) nor DIZE were able to blunt Ang II-mediated aldosterone synthase expression. Collectively these results suggest that the ACE2/Ang-(1–7)/MasR axis is unlikely to counteract aldosterone biosynthesis under conditions of enhanced aldosterone secretion as PA and heart failure.