The bradykinin B2 receptor antagonist icatibant (Hoe 140) blocks aminopeptidase N at micromolar concentrations: Off-target alterations of signaling mediated by the bradykinin B1 and angiotensin receptors

The N-terminal sequence of icatibant, a widely used peptide antagonist of the bradykinin B2 receptors, is analogous to that of other known aminopeptidase N inhibitors. Icatibant competitively inhibited the hydrolysis of l-Ala-p-nitroanilide by recombinant aminopeptidase N (Ki 9.1 μM). In the rabbit aorta, icatibant (10–30 μM) potentiated angiotensin III, but not angiotensin II (contraction mediated by angiotensin AT1 receptors), and Lys-des-Arg9-bradykinin, but not des-Arg9-bradykinin (effects mediated by the bradykinin B1 receptors), consistent with the known susceptibility of these agonists to aminopeptidase N. At concentrations possibly reached in vivo (e.g., in kidneys), icatibant alters physiological systems different from bradykinin B2 receptors.