A new strategy for treating hypertension by blocking the activity of the brain renin–angiotensin system with aminopeptidase A inhibitors

Hypertension affects one-third of the adult population and is a growing problem due to the increasing incidence of obesity and diabetes. Brain RAS (renin–angiotensin system) hyperactivity has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. We have identified in the brain RAS that APA (aminopeptidase A) and APN (aminopeptidase N), two membrane-bound zinc metalloproteases, are involved in the metabolism of AngII (angiotensin II) and AngIII (angiotensin III) respectively. The present review summarizes the main findings suggesting that AngIII plays a predominant role in the brain RAS in the control of BP (blood pressure). We first explored the organization of the APA active site by site-directed mutagenesis and molecular modelling. The development and the use in vivo of specific and selective APA and APN inhibitors EC33 and PC18 respectively, has allowed the demonstration that brain AngIII generated by APA is one of the main effector peptides of the brain RAS, exerting a tonic stimulatory control over BP in conscious hypertensive rats. This identified brain APA as a potential therapeutic target for the treatment of hypertension, which has led to the development of potent orally active APA inhibitors, such as RB150. RB150 administered orally in hypertensive DOCA (deoxycorticosteroneacetate)-salt rats or SHRs (spontaneously hypertensive rats) crosses the intestinal, hepatic and blood–brain barriers, enters the brain, generates two active molecules of EC33 which inhibit brain APA activity, block the formation of brain AngIII and normalize BP for several hours. The decrease in BP involves two different mechanisms: a decrease in vasopressin release into the bloodstream, which in turn increases diuresis resulting in a blood volume reduction that participates in the decrease in BP and/or a decrease in sympathetic tone, decreasing vascular resistance. RB150 constitutes the prototype of a new class of centrally acting antihypertensive agents and is currently being evaluated in a Phase Ib clinical trial. Abbreviations: ACE, angiotensin-converting enzyme; ACEI, angiotensin-converting enzyme inhibitor; AGT, angiotensinogen; AngI etc., angiotensin I etc; Ang-(1–7), angiotensin-(1–7); APA, aminopeptidase A; APN, aminopeptidase N; AT1R, AngII type 1 receptor; AT2R, AngII type 2 receptor; AVP, arginine-vasopressin; BBB, blood–brain barrier; BP, blood pressure; DOCA, deoxycorticosterone acetate; GluPO3H2, 4-amino-4 phosphonobutyric acid; GluSH, glutamate thiol; HR, heart rate; i.c.v., intracerebroventricular(ly); LTA4H, leukotriene A4 hydrolase; MABP, mean arterial BP; NEP, neutral endopeptidase 24.11; NOAEL, no observed adverse effect level; NTS, nucleus of the tractus solitaries; OVLT, organum vasculosum of the lamina terminalis; p.o., per os; PVN, paraventricular nucleus; RAS, renin–angiotensin system; RVLM, rostroventrolateral medulla; SFO, subfornical organ; SHR, spontaneously hypertensive rat; SON, supraoptic nucleus; WKY, Wistar–Kyoto