Potentiation of the Actions of Bradykinin by Angiotensin I–Converting Enzyme Inhibitors

Abstract

Part of the beneficial effects of angiotensin I-converting enzyme (ACE) inhibitors are due to augmenting the actions of bradykinin (BK). We studied this effect of enalaprilat on the binding of [3H]BK to Chinese hamster ovary (CHO) cells stably transfected to express the human BK B2 receptor alone (CHO-3B) or in combination with ACE (CHO-15AB). In CHO-15AB cells, enalaprilat (1 mumol/L) increased the total number of low-affinity [3H]BK binding sites on the cells at 37 degrees C, but not at 4 degrees C, from 18.4 +/- 4.3 to 40.3 +/- 11.9 fmol/10(6) cells (P < .05; Kd, 2.3 +/- 0.8 and 5.9 +/- 1.3 nmol/L; n = 4). Enalaprilat preserved a portion of the receptors in high-affinity conformation (Kd, 0.17 +/- 0.08 nmol/L; 8.1 +/- 0.9 fmol/10(6) cells). Enalaprilat decreased the IC50 of [Hyp3-Tyr(Me)8]BK, the BK analogue more resistant to ACE, from 3.2 +/- 0.8 to 0.41 +/- 0.16 nmol/L (P < .05, n = 3). The biphasic displacement curve of the binding of [3H]BK also suggested the presence of high-affinity BK binding sites. Enalaprilat (5 nmol to 1 mumol/L) potentiated the release of [3H]arachidonic acid and the liberation of inositol 1,4,5-trisphosphate (IP3) induced by BK and [Hyp3-Tyr(Me)8]BK. Moreover, enalaprilat (1 mumol/L) completely and immediately restored the response of the B2 receptor, desensitized by the agonist (1 mumol/L [Hyp3-Tyr(Me)8]BK); this effect was blocked by the antagonist, HOE 140. Finally, enalaprilat, but not the prodrug enalapril, decreased internalization of the receptor from 70 +/- 9% to 45 +/- 9% (P < .05, n = 7). In CHO-3B cells, enalaprilat was ineffective. ACE inhibitors in the presence of both the B2 receptor and ACE enhance BK binding, protect high-affinity receptors, block receptor desensitization, and decrease internalization, thereby potentiating BK beyond blocking its hydrolysis.

Novel Mode of Action of Angiotensin I Converting Enzyme Inhibitors

“…Although ACEIs do not directly affect the BK B 2 receptor, they augment its function when ACE is also expressed on the cell surface (12)(13)(14). Here we report that ACEIs in nanomolar concentrations directly activate the BK B 1 receptor in cells without an intermediate peptide ligand and in the absence of ACE.…”

“…Because ACE has a dual action, it activates angiotensin I and inactivates BK by cleaving C-terminal dipeptides (9, 18, 28), and its inhibitors block the release of the potent vasoconstrictor and mitogen angiotensin II and augment activation of the B 2 receptor by BK. Besides preventing kinin inactivation by ACE (10), these inhibitors indirectly potentiate B 2 because they induce an ACE/B 2 receptor cross-talk (12)(13)(14). Des-Arg 10 -kallidin is the endogenous ligand that potently activates the second kinin receptor, B 1 , at a low concentration (15).…”

“…(14). Fura-2 fluorescence was detected at 510 nm following excitation at 340 and 380 nm, and the ratio of intensities at 340 and 380 nm were recorded in 10 -100 cells simultaneously (12)(13)(14).…”

“…The inhibition of ACE or kininase II blocks angiotensin II release or bradykinin (BK) inactivation (9 -11), but these actions alone do not fully explain their effectiveness (5). ACEIs also potentiate the effects of BK and its ACE-resistant analogs on their B 2 receptor by inducing an enzyme/receptor protein-protein interaction (12)(13)(14), a heterodimer formation (14).…”

Reinventing the ACE inhibitors: some old and new implications of ACE inhibition

“…This protects high-affinity receptors, blocks receptor desensitization and decreases internalization, thereby potentiating BK beyond blocking its hydrolysis. 156,157 ACEis also directly activate the bradykinin B 1 receptor by acting at the zinc-binding pentameric consensus sequence HEXXH (195)(196)(197)(198)(199) of the B 1 receptor, a motif that is present in the active center of ACE but absent from the B 2 receptor. ACEis, when activating the B1 receptor, elevate intracellular calcium ([Ca 2+ ]i) and release NO from cultured cells.…”