Assessment of biological activity of novel peptide analogues of angiotensin IV

Abstract

Angiotensin IV (Ang IV) is a metabolite of angiotensin II which acts on specific AT(4) receptors identified as the enzyme insulin regulated aminopeptidase (IRAP). The transduction process of these receptors is unresolved, but Ang IV inhibits the aminopeptidase activity. Ang IV improves cognition in animal models thus there is a desire to develop metabolically stable analogues for further development. Peptide analogues of Ang IV were obtained commercially or synthesised. Each peptide was tested in vitro for its ability to inhibit the aminopeptidase activity (IRAP) of mouse brain homogenates and for its effects on isolated rat uterine smooth muscle. [Des-Val(1) ]-Ang IV, acetylated-Ang IV-amide, Ang IV-amide and [des-His(4) ]-Ang IV all inhibited IRAP. [Sar(1) , Ile(8) ]-Angiotensin II (10 µm) had an effect greater than that of Ang IV or any of the other analogues studied. In isolated uterine smooth muscle, angiotensins II and IV induced contractions, which could be antagonised by an AT(1) -receptor antagonist. None of the novel peptides induced uterine smooth muscle contractions, but [Sar(1) , des Arg(2) -Gly(8) ]-angiotensin II showed significant antagonism of the contractile effects of angiotensin II and carboxyamide-terminated Ang IV-NH(2) showed antagonism of Ang IV-induced contractions. This study provides five novel inhibitors of IRAP worthy of assessment in behavioural models of learning and memory. The analogues are devoid of AT(1) receptor agonist properties, and the carboxyamide analogue presents an opportunity to elucidate the mechanism of action of Ang IV as, like Ang IV, it inhibits IRAP, but antagonises the effects of Ang IV on isolated smooth muscle.