Abstract
Previous analyses support that aminopeptidase N is a major inactivation pathway for high-affinity peptide ligands of the human and rabbit forms of the kinin B1 receptor (agonists or antagonists). In this study, we found that the high-affinity antagonist B-9958 (Lys-Lys-[Hyp3, CpG5, d-Tic7, CpG8]des-Arg9-BK; des-Arg9-BK, des-arginine9-bradykinin) is an aminopeptidase N substrate based on its capacity to compete for the hydrolysis of the chromogenic substrate l-Ala-p-nitroanilide by membranes isolated from human or rabbit arterial smooth muscle cells, its inactivation in the presence of these membranes (radioreceptor assay) and on its intense potentiation by the aminopeptidase N inhibitor amastatin in the rabbit aorta contractility assay (gain of 0.84 units in the pA2 scale). Analogs of B-9958 in which the N-terminal Lys residue was substituted by d-Lys or d-Arg (B-10352 and B-10356, respectively) showed reduced affinity at the human or rabbit B1 receptors (1.2–2.8-fold), as estimated by the displacement of [3H]Lys-des-Arg9-BK binding, but were more potent antagonists of des-Arg9-BK-induced contraction of the rabbit aorta than B-9958 in the absence of amastatin; they were not potentiated by the latter inhibitor. Unexpectedly, B-10356 inhibited l-Ala- p-nitroanilide hydrolysis without being inactivated, suggesting that it is an aminopeptidase N inhibitor. This was verified because B-10356 (but not B-10352) potentiated peptides unrelated to kinins but susceptible to aminopeptidase N inactivation (angiotensin III, thrombin receptor hexapeptide agonist). B-10356 inhibits dual molecular targets (aminopeptidase N enzyme Ki, 0.9–2.2 μM; kinin B1 receptor binding Ki, 0.5–1.5 nM), and this may be an advantage for specific therapeutic applications (e.g., inhibition of angiogenesis).
Footnotes
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This work was supported by the Canadian Institutes of Health Research (Grant MOP-14077) and by the Fonds de la Recherche en Santé du Québec (Studentship Award to J.-P.F.).
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doi:10.1124/jpet.105.095661.
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ABBREVIATIONS: des-Arg9-BK, des-arginine9-bradykinin; B-9958, Lys-Lys-[Hyp3, CpG5, d-Tic7, CpG8]des-Arg9-BK; B-10350, Lys-Lys-[Hyp3, Igl5, d-Tic7, CpG8]des-Arg9-BK; l-Ala-pNA, l-alanine-p-nitroanilide; HPLC, high-pressure liquid chromatography; NAT6-NH2, new amino-terminal hexapeptide from the cleaved thrombin receptor, amide form; B-10352, d-Lys isomer of B-9958; B-10356, d-Arg analog of B-9958; Hoe 140, d-Arg[Hyp3, Thi5, d-Tic7, Oic8]-BK; NPC 1773, d-Arg[Hyp3, d-HypE(transpropyl)7, Oic8]-BK.
- Received September 15, 2005.
- Accepted December 19, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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