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In the brain, aminopeptidase A (APA), a membrane-bound zinc metalloprotease, generates angiotensin III from angiotensin II. Brain angiotensin III exerts a tonic stimulatory effect on the control of blood pressure (BP) in hypertensive rats and increases vasopressin release. Blocking brain angiotensin III formation by the APA inhibitor prodrug RB150/firibastat normalizes arterial BP in hypertensive deoxycorticosterone acetate (DOCA)-salt rats without inducing angiotensin II accumulation. We therefore hypothesized that another metabolic pathway of brain angiotensin II, such as the conversion of angiotensin II into angiotensin 1-7 (Ang 1-7) by angiotensin-converting enzyme 2 (ACE2) might be activated following brain APA inhibition. We found that the intracerebroventricular (icv) administration of RB150/firibastat in conscious DOCA-salt rats both inhibited brain APA activity and induced an increase in brain ACE2 activity. Then, we showed that the decreases in BP and vasopressin release resulting from brain APA inhibition with RB150/firibastat were reduced if ACE2 was concomitantly inhibited by MLN4760, a potent ACE2 inhibitor, or if the Mas receptor (MasR) was blocked by A779, a MasR antagonist. Our findings suggest that in the brain, the increase in ACE2 activity resulting from APA inhibition by RB150/firibastat treatment, subsequently increasing Ang 1-7 and activating the MasR while blocking angiotensin III formation, contributes to the antihypertensive effect and the decrease in vasopressin release induced by RB150/firibastat. RB150/firibastat treatment constitutes an interesting therapeutic approach to improve BP control in hypertensive patients by inducing in the brain renin–angiotensin system, hyperactivity of the beneficial ACE2/Ang 1-7/MasR axis while decreasing that of the deleterious APA/Ang II/Ang III/ATI receptor axis.

Background and objective Hyperactivity of the brain renin-angiotensin (Ang) system has been implicated in the development and maintenance of hypertension. AngIII, one of the main effector peptides of the brain renin-Ang system, exerts a tonic stimulatory control over blood pressure (BP) in hypertensive rats. Aminopeptidase A (APA), the enzyme generating brain AngIII, represents a new therapeutic target for the treatment of hypertension. We developed RB150, a prodrug of the specific and selective APA inhibitor, EC33. When given orally in acute treatment in hypertensive rats, RB150 crosses the gastrointestinal and blood-brain barriers, enters the brain, inhibits brain APA activity and decreases BP. We investigate, here, the antihypertensive effects of chronic oral RB150 (50 mg/kg per day) treatment over 24 days in alert hypertensive deoxycorticosterone acetate-salt rats. Methods We measured variations in Brain APA enzymatic activity, SBP, plasma arginine vasopressin levels and metabolic parameters after RB150 chronic administration. Results This resulted in a significant decrease in SBP over the 24-day treatment period showing that no tolerance to the antihypertensive RB150 effect was observed throughout the treatment period. Chronic RB150 treatment also significantly decreased plasma arginine vasopressin levels and increased diuresis, which participate to BP decrease by reducing the size of fluid compartment. Interestingly, we observed an increased natriuresis without modifying both plasma sodium and potassium levels. Conclusion Our results strengthen the interest of developing RB150 as a novel central-acting antihypertensive agent and evaluating its efficacy in salt-sensitive hypertension.

The hyperactivity of the brain renin–angiotensin system (RAS) has been implicated in the development and maintenance of arterial hypertension (HTA). Our aim was to demonstrate that normalizing brain RAS hyperactivity could constitute a new therapeutic approach for HTA treatment We first demonstrated in the brain that aminopeptidase A (APA) is the enzyme generating angiotensin III (AngIII) from AngII. Then, using the specific and selective APA inhibitor, EC33 ((3S)-3-amino-4-sulfanyl-butane-1-sulfonic acid), we showed that AngIII is one of the main effector peptides of the brain RAS, exerting a tonic stimulatory control over blood pressure (BP) in hypertensive rats. This suggests that brain APA may be a potential therapeutic target for HTA treatment. We then designed RB150 {4,4-dithio[bis(3-aminobutyl sulfonic acid)]}, an orally active prodrug of EC33. RB150, given orally in conscious deoxycorticosterone acetate-salt (DOCA-salt) rats or spontaneously hypertensive rats, crosses the intestinal, hepatic and blood-brain barriers, enters the brain, where it is cleaved by brain reductases, generating two active molecules of EC33 which inhibit brain APA activity, block the formation of brain AngIII and induce a marked and sustained decrease in BP. The RB150-induced BP decrease is due to a reduced vasopressin release, which increases diuresis, reducing extracellular volume, a decrease in sympathetic tone, leading to a reduction of vascular resistances and the improvement of the baroreflex function (Figure below). RB150 was renamed firibastat by OMS. Phase Ia/Ib clinical trials showed that firibastat is clinically and biologically well-tolerated in healthy volunteers. Firibastat could constitute the first drug candidate of a new class of antihypertensive agents targeting the brain RAS, the clinical efficacy of which (Phase IIa and Phase IIb) in hypertensive patients was achieved. Acknowledgement/Funding INSERM, College de France, ANR LabCom, Quantum Genomics