International Union of Basic and Clinical Pharmacology. CXXI. Apelin receptor pharmacology in the human cardiovascular system and emerging clinical applications

The apelin receptor binds 2 families of endogenous peptide, apelin and Elabela, but unusually these share little sequence similarity in the N-terminal sequences of the binding domains. Cryo-electron microscopy, X-ray crystallography combined with AlphaFold has yielded a molecular map of the interaction of amino acids with the apelin receptor in complex with endogenous peptides and biased ligands. In the early embryo, the apelin signaling pathway is essential for cardiovascular development, with receptor knockout models displaying severe cardiovascular defects. In adults, the principal short-term effects of [Pyr¹]apelin-13, infused into healthy volunteers was increased cardiac output and decreased peripheral resistance without side effects. Importantly, these beneficial effects of systemic apelin were retained in patients with heart failure and pulmonary arterial hypertension. In chronic kidney disease, [Pyr¹]apelin-13 showed additional therapeutic potential, increasing glomerular filtration rate while reducing proteinuria. Identification of these favorable actions in disease has sparked the development of more effective agonists with improved pharmacokinetics and pharmacodynamics profiles. Among these are G protein-biased peptide agonists, designed to minimize receptor desensitization by reducing internalization via the β-arrestin pathway. These have shown efficacy in proof-of-concept studies and in animal models of pulmonary arterial hypertension, one of the most promising therapeutic targets. This review focuses on the clinical pharmacology of the apelin receptor, exploring the pathophysiology of diseases where the apelin signaling pathway is dysregulated that have emerged during the last 5 years. SIGNIFICANCE STATEMENT: This review focuses on the pharmacology of the apelin receptor where structural analysis has generated a molecular map of interaction with endogenous ligands, apelin and Elabela, as well as with peptide and small molecule agonists. Novel unbiased and biased apelin agonists are progressing through the clinic targeting pathophysiological conditions where the apelin signaling pathway is dysregulated.