Adropin

Adropin is a 76-amino-acid secreted peptide encoded by the Energy Homeostasis Associated (Enho) gene, first identified in 2008 by Kumar et al. (Cell Metabolism) through microarray profiling of liver gene expression in melanocortin-3 receptor knockout (Mc3r-/-) mice on a C57BL/6J background [1]. The name derives from the Latin aduro (to set fire to) and pinquis (fat or greasy), reflecting the original observation that hepatic Enho expression is acutely upregulated by short-term high-fat feeding and suppressed in states of diet-induced obesity and prolonged caloric excess. The biologically active secreted domain spans amino acids 34 through 76, with residues 1 through 33 constituting a signal peptide that directs membrane anchoring and extracellular release. Human, mouse, and rat adropin amino acid sequences are 100 percent identical, a degree of conservation unusual among metabolic peptides and suggestive of strong functional constraint across mammalian species. The mature peptide has a molecular weight of approximately 4,499 daltons and functions both as a soluble circulating factor and as a membrane-bound protein facilitating intercellular communication through the Notch signaling pathway in the central nervous system. The biological effects of adropin are mediated principally through two receptor systems: the orphan G protein-coupled receptor 19 (GPR19), which couples to downstream MAPK and Akt signaling cascades in cardiomyocytes and other cell types; and vascular endothelial growth factor receptor 2 (VEGFR2), through which adropin upregulates endothelial nitric oxide synthase (eNOS) expression via the PI3K-Akt and ERK1/2 pathways to promote nitric oxide release, endothelial cell proliferation, migration, and capillary tube formation. Lovren et al. (2010) demonstrated in Circulation that adropin-treated human umbilical vein endothelial cells exhibited enhanced proliferation, migration, and tube formation with reduced permeability and tumor necrosis factor-induced apoptosis [2]. In the original Kumar et al. characterization, transgenic overexpression or systemic adropin treatment in diet-induced obese mice attenuated hepatosteatosis and insulin resistance independently of effects on adiposity or food intake, with adropin regulating expression of hepatic lipogenic genes (fatty acid synthase, stearoyl-CoA desaturase 1) and adipose tissue peroxisome proliferator-activated receptor gamma [1]. Preclinical pharmacology has expanded substantially beyond metabolic endpoints: in experimental ischemic stroke models, synthetic adropin administered intravenously at 900 to 2,700 nmol/kg at the onset of or up to 3 hours after permanent middle cerebral artery occlusion dose-dependently reduced infarct size, blood-brain barrier disruption, tight junction protein degradation, matrix metalloproteinase-9 activity, oxidative stress, and neutrophil infiltration through an eNOS-dependent mechanism, as adropin therapy failed to confer neuroprotection in eNOS-deficient mice [3, 4]. Additional preclinical work has demonstrated anti-atherosclerotic activity through suppression of monocyte-endothelial cell adhesion and smooth muscle cell proliferation [5], preservation of the blood-brain barrier after intracerebral hemorrhage through a Notch1/Hes1 pathway [6], and restoration of cardiac glucose oxidation in pre-diabetic obese mice through modulation of the mitochondrial acetyltransferase GCN5L1 [7]. Clinical studies in humans are predominantly observational: serum adropin levels are consistently and significantly lower in patients with coronary artery disease, acute myocardial infarction, metabolic syndrome, type 2 diabetes mellitus, polycystic ovary syndrome, and obstructive sleep apnea compared to healthy controls, with inverse correlations between adropin concentration and disease severity scores including the SYNTAX score for coronary atherosclerotic burden [8, 9, 10]. A meta-analysis by Zheng et al. (2019) encompassing 7 case-control studies with 525 coronary artery disease patients and 420 controls confirmed the consistent inverse association [8]. No human interventional trials of exogenous adropin administration have been published as of the most recent monograph revision. The compound is available as a synthetic research peptide from multiple suppliers (Phoenix Pharmaceuticals, Bachem, Creative Peptides, GenScript) typically as adropin (34-76), the biologically active fragment, at greater than 95 percent purity by HPLC. This monograph reviews the discovery and gene characterization; the amino acid sequence, structure, and synthesis; the dual-receptor molecular pharmacology through GPR19 and VEGFR2-eNOS; the tissue distribution and nutritional regulation of Enho expression; the preclinical pharmacology across metabolic, cardiovascular, and neurological models; the clinical observational evidence base; sourcing and quality verification; reconstitution and handling; stack interactions; adverse events and safety considerations; and a comparative assessment of five metabolic-regulatory peptide candidates (irisin, FGF21, GDF15, apelin, MOTS-c) against adropin on five competency standards.