Discovery of a competitive apelin receptor (APJ) antagonist.

The apelin receptor (APJ) is a class A G-protein-coupled receptor (GPCR) and is a putative target for the treatment of cardiovascular and metabolic diseases. Apelin-13 (NH2-QRPRLSHKGPMPF-COOH) is a vasoactive peptide and one of the most potent endogenous inotropic agents identified to date. We report the design and discovery of a novel APJ antagonist. By using a bivalent ligand approach, we have designed compounds with two 'affinity' motifs and a short series of linker groups with different conformational and non-bonded interaction properties. One of these, cyclo(1-6)CRPRLC-KH-cyclo(9-14)CRPRLC is a competitive antagonist at APJ. Radioligand binding in CHO cells transfected with human APJ gave a K(i) value of 82 nM, competition binding in human left ventricle gave a K(D) value of 3.2 µM, and cAMP accumulation assays in CHO-K1-APJ cells gave a K(D) value of 1.32 µM.

Modulation of the apelin/APJ system in heart failure and atherosclerosis in man.

BACKGROUND AND PURPOSE: The aim of this study was to determine whether the apelin/APJ system is altered in human cardiovascular disease by investigating whether the expression of apelin or its receptor is altered at the protein level. EXPERIMENTAL APPROACH: Radioligand binding studies were used to determine apelin receptor density in human cardiac tissues. Apelin peptide levels in cardiovascular tissues were determined by radioimmunoassay. In vitro pharmacology was used to assess vasoactive properties of apelin in human coronary artery. Localization of apelin and its receptor in coronary artery was determined using immunohistochemistry. KEY RESULTS: Apelin receptor density was significantly decreased in left ventricle from patients with dilated cardiomyopathy or ischaemic heart disease compared with controls, but apelin peptide levels remained unchanged. Apelin was up-regulated in human atherosclerotic coronary artery and this additional peptide localized to the plaque, colocalizing with markers for macrophages and smooth muscle cells. Apelin potently constricted human coronary artery. CONCLUSIONS AND IMPLICATIONS: We have detected changes in the apelin/APJ system in human diseased cardiac and vascular tissue. The decrease in receptor density in heart failure may limit the positive inotropic actions of apelin, contributing to contractile dysfunction. The contribution of the increased apelin levels in atherosclerotic coronary artery to disease progression remains to be determined. These data suggest a potential role for the apelin/APJ system in human cardiovascular disease.

International Union of Basic and Clinical Pharmacology. LXXIV. Apelin receptor nomenclature, distribution, pharmacology, and function.

A gene encoding a novel class a G-protein-coupled receptor was discovered in 1993 by homology cloning and was called APJ. It was designated an "orphan" receptor until 1998, when its endogenous ligand was identified and named apelin (for APJ endogenous ligand). Since this pairing, both apelin and its receptor have been found to have a widespread distribution in both the central nervous system and the periphery. A number of physiological and pathophysiological roles for the receptor have emerged, including regulation of cardiovascular function, fluid homeostasis, and the adipoinsular axis. This review outlines the official International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification nomenclature, designating the receptor protein as the apelin receptor, together with current knowledge of its pharmacology, distribution, and functions.

[Pyr1]apelin-13 identified as the predominant apelin isoform in the human heart: vasoactive mechanisms and inotropic action in disease.

Apelin receptors, present on vascular smooth muscle cells, endothelium, and cardiomyocytes, are activated by the family of apelin peptides to elicit cardiovascular effects in experimental animals, but functional activity in humans has not been studied in detail. We detected low levels of apelin immunoreactivity in plasma of volunteers consistent with an autocrine/paracrine action and detected apelin immunoreactivity in the supernatant from human cultured endothelial cells. We found that [Pyr(1)]apelin-13 was the predominant isoform in cardiac tissue from patients with coronary artery disease. We tested the hypothesis that apelins have vascular and cardiac actions in human tissues in vitro and compared responses to [Pyr(1)]apelin-13, apelin-13, and apelin-36. In endothelium-intact mammary artery, all 3 of the apelins induced concentration-dependent vasodilatation with comparable potency (EC(50): 0.6 to 1.6 nM; maximum response: 40% to 50%). Vasodilatation was abolished after endothelial removal or preincubation with indomethacin but was unaffected by preincubation with N(G)-nitro-L-arginine methyl ester, indicating involvement of prostanoids but not NO in dilatation by apelins in this patient group. Apelins were potent constrictors of endothelium-denuded saphenous vein (EC(50): 0.6 to 1.6 nM; maximum response: 17% to 26%) and mammary artery ([Pyr(1)]apelin-13; EC(50): 0.2 nM; maximum response: 29%). In paced atrial strips, all 3 of the peptides increased the force of contraction with subnanomolar potencies (EC(50): 40 to 125 pM). For the first time, we demonstrate that the 3 principal forms of apelin have comparable potency and efficacy in human cardiovascular tissues. Apelins are potent endothelium-dependent vasodilators acting via a prostanoid-dependent mechanism; however, removal of the endothelium revealed direct vasoconstrictor actions in both the artery and vein. Furthermore, in human cardiac tissue, the apelin peptides are among the most potent endogenous positive inotropic agents yet reported.