A Systematic Exploration of Macrocyclization in Apelin-13: Impact on Binding, Signaling, Stability, and Cardiovascular Effects

The apelin receptor generates increasing interest as a potential target across several cardiovascular indications. However, the short half-life of its cognate ligands, the apelin peptides, is a limiting factor for pharmacological use. In this study, we systematically explored each position of apelin-13 to find the best position to cyclize the peptide, with the goal to improve its stability while optimizing its binding affinity and signaling profile. Macrocyclic analogues showed a remarkably higher stability in rat plasma (half-life >3 h versus 24 min for Pyr-apelin-13), accompanied by improved affinity (analogue 15, Ki 0.15 nM and t1/2 6.8 h). Several compounds displayed higher inotropic effects ex vivo in the Langendorff isolated heart model in rats (analogues 13 and 15, maximum response at 0.003 nM versus 0.03 nM of apelin-13). In conclusion, this study provides stable and active compounds to better characterize the pharmacology of the apelinergic system.apelin受体（apelin receptor）作为多种心血管适应症的潜在治疗靶点，正日益受到广泛关注。然而其同源配体——apelin肽（apelin peptides）的半衰期极短，成为其药理学应用的一大限制因素。本研究系统探究了apelin-13的各个位点，以确定该肽的最佳环化位点，旨在在优化其结合亲和力与信号转导特性的同时提升其稳定性。大环类肽衍生物在大鼠血浆中的稳定性显著提升（半衰期＞3小时，而Pyr-apelin-13的半衰期仅为24分钟），同时结合亲和力也得到改善（如衍生物15的Ki值为0.15 nM，半衰期t1/2为6.8小时）。多款化合物在大鼠朗格多夫离体心脏模型（Langendorff isolated heart model）中展现出更强的离体正性肌力作用（如衍生物13与15，其最大响应浓度为0.003 nM，而apelin-13的最大响应浓度为0.03 nM）。综上，本研究获得了稳定且具有活性的化合物，可用于更深入地表征apelin能系统（apelinergic system）的药理学特性。