Elabela

Elabela (ELA), also designated Apela, Toddler, and Ende, is a secreted peptide hormone encoded by the APELA gene on human chromosome 4q32.3. The gene encodes a 54-amino-acid preproprotein containing a 22-residue signal peptide; cleavage yields the 32-amino-acid mature peptide ELA-32 (sequence QRPVNLTMRRKLRKHNCLQRRCMPLHSRVPFP), which may be further processed by proprotein convertases to generate the bioactive isoforms ELA-21 and ELA-11 [1, 2]. Elabela was discovered independently by two groups in 2013 and 2014: Chng et al. (2013) identified the peptide in zebrafish as a hormone essential for heart development signaling through the apelin receptor (APLNR/APJ), while Pauli et al. (2014) characterized the same molecule as "Toddler," an embryonic signal promoting mesodermal cell migration [1, 3]. The peptide is the second endogenous ligand of the apelin receptor, a class A G-protein-coupled receptor previously known to bind only apelin; despite sharing a common receptor, Elabela and apelin exhibit less than 25 percent sequence similarity and display distinct spatiotemporal expression profiles and partially divergent signaling bias [4, 5]. Elabela activates the apelin receptor through Gi/o-coupled inhibition of adenylyl cyclase, stimulation of ERK1/2 and PI3K/AKT/mTOR pathways, mobilization of intracellular calcium, and recruitment of beta-arrestin, functioning as a balanced agonist across G-protein-dependent and beta-arrestin-dependent pathways [5, 6]. The binding affinity of ELA-32 for the human apelin receptor is high, with reported IC50 values of approximately 0.27 nanomolar and Kd values of approximately 0.51 nanomolar [7]. Physiologically, Elabela is expressed at high levels during embryogenesis across vertebrate species and in adult tissues with restricted distribution, principally kidney (collecting ducts and loops of Henle), prostate, and vascular endothelium [2, 8]. The peptide is essential for vertebrate cardiovascular development: genetic ablation of Elabela in zebrafish produces severe cardiac malformations including rudimentary or absent hearts, phenocopying loss of the apelin receptor itself [1]. In mice, Elabela knockout produces preeclampsia-like symptoms during pregnancy including proteinuria, hypertension, defective placental angiogenesis, and reduced fetal weight, effects that are rescued by exogenous ELA infusion [9]. A separate demonstration by Ho et al. (2015) established that Elabela is an endogenous growth factor sustaining human embryonic stem cell self-renewal via the PI3K/AKT pathway, with CRISPR-mediated deletion causing loss of pluripotency and cell death [10]. In the adult cardiovascular system, Elabela functions as an endogenous agonist of the apelin receptor producing positive inotropy, vasodilation, increased cardiac output, and depressor responses comparable to apelin; expression is downregulated in pulmonary arterial hypertension, and exogenous administration attenuates right ventricular hypertrophy and pulmonary vascular remodeling in monocrotaline-exposed rats [11]. Preclinical cardioprotective activity has been demonstrated across myocardial infarction, ischemia-reperfusion injury, and hypertensive cardiac fibrosis models, operating through PI3K/AKT-mediated anti-apoptotic, anti-fibrotic, and pro-angiogenic mechanisms [12, 13, 14]. Renoprotective activity is characterized by antagonism of the intrarenal renin-angiotensin system, reduction of blood pressure and albuminuria in salt-sensitive hypertensive rats, and prevention of vasopressin-induced aquaporin-2 translocation in collecting duct principal cells, thereby promoting aqueous diuresis [15, 16]. Neuroprotective activity has been demonstrated in rodent models of ischemic stroke, where ELA attenuates neuronal apoptosis, ferroptosis, and pyroptosis through APJ-dependent signaling cascades [17, 18]. The in vitro plasma half-life of ELA-32 in human plasma is approximately 47 minutes, substantially longer than that of apelin-13 (approximately 5 minutes in vivo), though rapid degradation occurs in kidney homogenates (half-life approximately 44 seconds), and the short systemic half-life has motivated the development of Fc-fusion, PEGylated, and acylated analogs with extended duration of action [19, 20, 21]. No human clinical trials of exogenous Elabela administration have been completed as of the monograph revision date; the compound remains in the preclinical-to-translational research phase. This monograph reviews the chemistry, isoform biology, and synthesis of Elabela; the receptor pharmacology and signaling mechanisms in molecular detail; the pharmacokinetic profile including metabolism and stability-enhancement strategies; the preclinical evidence base across cardiovascular, renal, obstetric, stem cell, neurological, and oncological applications; sourcing and quality verification for research-grade material; reconstitution and handling; stack-interaction considerations; the adverse-event and safety signal from animal studies; and a comparative assessment of five apelinergic system candidates against Elabela on five competency standards.