Aminopeptidase A: A Potential Novel Therapy for Angiotensin-Dependent Hypertension?

Background: We have shown that mice with a genetic deficiency in Aminopeptidase A (APA) have elevated blood pressure. APA is an enzyme that removes a single aspartate residue from the amino-terminus of several peptides in the renin-angiotensin systems (RAS), including angiotensin (Ang) II. In this study, we investigated the impact of a recombinant APA on the formation of various RAS peptides and its effect on blood pressure. Methods: An in vitro assay was used to identify Ang peptides as substrates for APA. Ang peptides identified as APA substrates using this assay were then injected to anesthetized WT and APA-deficient mice to assess their pressor effect by measuring systolic blood pressure (SBP). Subsequently, murine recombinant (r)APA was used to evaluate its action on the acute SBP elevation elicited by Ang peptides that were identified to trigger pressor response. Results: In the in vitro assay, Ang II (22427±3353, n=12), Ang I (21883±1692, n=3), Ang1-7 (15833±3395, n=3), Ang1-9 (15773±3395, n=3) and Ang1-12 (13170±220, n=3), were identified as a substrate for rAPA as indicated by a strong aspartate-driven fluorescence formation. When these five Ang peptides were administered to WT mice, only Ang I, Ang II and Ang 1-12 caused a significant increase in SBP. This effect was exaggerated in APA deficient mice. The SBP increase elicited by Ang I and Ang II in WT mice was markedly reduced by the pre-administration of rAPA (Fig. 1). Conclusion: Aminopeptidase A can cleave the N-terminal aspartate from Ang II as well as from other RAS peptides that elicit (Ang 1-12, Ang I) do not elicit (Ang 1-9, Ang 1-7) pressor response in mice. APA deficiency is associated with an exaggerated SBP response to Ang I, Ang II and Ang 1-12 while the recombinant enzyme mitigates the acute hypertensive effect. rAPA markedly reduced the increase in SBP caused by Ang I and Ang II infusion suggesting that it may be used to treat hypertension resulting from RAS overactivity.