Angiotensin I-Converting Enzyme Inhibitors Block Protein Kinase Cϵ by Activating Bradykinin B₁ Receptors in Human Endothelial Cells

Abstract

Angiotensin I-converting enzyme (ACE) inhibitors are widely used to treat patients with cardiovascular and kidney diseases, but inhibition of ACE alone does not fully explain the beneficial effects. We reported that ACE inhibitors directly activate bradykinin B₁ receptor at the canonical Zn²⁺ binding site, leading to prolonged nitric oxide (NO) production in endothelial cells. Protein kinase C (PKC) ϵ, a novel PKC isoform, is up-regulated in myocardium after infarction, suggesting a role in the development of cardiac dysfunction. In cytokine-treated human lung microvascular endothelial cells, B₁ receptor activation by ACE inhibitors (enalaprilat, quinaprilat) or peptide ligands (des-Arg¹⁰-Lys¹-bradykinin, des-Arg⁹-bradykinin) inhibited PKCϵ with an IC₅₀ = 7 × 10^–9 M. Despite the reported differences in binding affinity to receptor, the two peptide ligands were equally active, even when inhibitor blocked the cleavage of Lys¹, thus the conversion by aminopeptidase. The synthetic undecapeptide (LLPHEAWHFAR) representing the binding site for ACE inhibitors on human B₁ receptors reduced PKCϵ inhibition by enalaprilat but not by peptide agonist. A combination of inducible and endothelial NO synthase inhibitors, 1400W [N-(3(aminomethyl) benzyl) acetamidine dihydrochloride] and Nω-nitro-l-arginine (2 μM), significantly reduced inhibition by enalaprilat (100 nM), whereas the NO donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino]diazen-1-ium-1,2-diolate (100 μM) inhibited PKCϵ activity just as the B₁ ligands did. In conclusion, NO generated by B₁ receptor activation inhibits PKCϵ.