Latent Bradykinin B ₂ Receptor Agonist: Differential Vascular and Hemodynamic Effects Dependent On The Effector Carboxypeptidases

Background We previously reported interesting vascular effects from C‐terminal extended bradykinin (BK) sequences that behave as protease‐activated B 2 receptor (B 2 R) agonists. Further to these studies, we designed and evaluated new “prodrug” peptides extended around the BK sequence, as potential ligands, that could be activated by vascular or blood plasma peptidases. We have explored the possibility of a controlled release of the direct agonist D‐Arg 0 ‐BK (r‐BK) by two cycles of Arg‐carboxypeptidases (CP) from D‐Arg 0 ‐BK‐Arg‐Arg (r‐BK‐RR). Methods The affinity of both peptides for recombinant B 2 R was assessed using a [ 3 H]BK binding displacement assay in the presence of protease/peptidase inhibitors. The vascular actions of these kinins were evaluated in human isolated umbilical vein, a contractile bioassay for the B 2 R, and in anaesthetized rats instrumented to record hemodynamic responses to bolus intravenous (i.v.) injection of increasing doses of r‐BK, r‐BK‐RR, in the absence or presence of specific inhibitors. Results r‐BK exhibited an affinity practically equal to that of BK for the rat myc‐B 2 R construction, while the C‐terminal prolongation of r‐BK decreased the receptor affinity, 61‐fold for r‐BK‐RR. In vascular preparations, r‐BK was found as a potent contractile agent essentially unaffected by the blockade of angiotensin converting enzyme (ACE) with enalaprilat, and/or Arg‐CP with Plummer's inhibitor. The contractile effect of r‐BK‐RR was found to be about 7‐fold less potent than r‐BK and was only slightly decreased by the Plummer's inhibitor. Enalaprilat alone, or combined with the Plummer's inhibitor, was more effective to shift the concentration‐effect curve of r‐BK‐RR to the right by a factor 3.5; suggesting the removal of the Arg‐Arg extension in a single step by ACE. In anesthetized rats, r‐BK and r‐BK‐RR were virtually equipotent hypotensive agents. Both peptides caused similar rapid, transient and dose‐related hypotensive effects, that were extensively inhibited by icatibant (a B 2 R antagonist). The hypotensive effects of r‐BK were potentiated by enalaprilat, but not influenced by the Arg‐CP inhibitor, which is consistent with a minor role of Arg‐CP in the metabolism of r‐BK. However, in rats pretreated with both enalaprilat and Plummer's inhibitor, the hypotensive responses and the duration of the hypotensive episode to r‐BK were significantly potentiated, revealing the involvement of Arg‐CP in cessation of the hypotensive episode when the metabolism of r‐BK by ACE is inhibited. The hypotensive responses to r‐BK‐RR were not affected by enalaprilat, but were significantly reduced by pre‐treatment with Arg‐CP inhibitor alone or combined with enalaprilat, pharmacologically evidencing r‐BK regeneration likely by two cycles of Arg‐carboxypeptidases (CP). Conclusions Altogether, these results indicate that (A) C‐terminally extended analog r‐BK‐RR is an indirect activator of the B 2 R, via its conversion to r‐BK, and (B) in anesthetized rats, Arg‐CP activity is dominant over ACE to regenerate a B 2 R agonist from r‐BK‐RR. Support or Funding Information Supported by the Canadian Institutes of Health Research and the Fonds de recherche‐Santé du Québec . This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

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