7562 Longitudinal Untargeted Proteomics of Leptin Administration in Lean Humans Under Short- And Long-Term Energy Deficiency: Novel Physiological Insights and Pleiotropic Immunomodulatory Effects From Two Randomized, Placebo-Controlled Clinical Trial

Abstract Disclosure: K. Stefanakis: None. M. Samiotaki: None. C.S. Mantzoros: None. Leptin is a known immunomodulator and exerts notable neuroendocrine functions, yet little is known about the full spectrum of downstream molecules and underlying mechanisms. We performed untargeted serum proteomics with liquid chromatography-tandem mass spectrometry (LC-MS/MS) across two studies a) short-term randomized controlled crossover study of lean male and female humans undergoing a 72-hour fast with concurrent administration of either placebo or high-dose leptin; b) long-term (36-week) randomized controlled trial of leptin replacement therapy in human females with acquired relative energy deficiency and hypoleptinemia. We explored longitudinal proteomic changes in FDR-corrected pre-to-post and between-group tests, as well as adjusted mixed models followed by post-hoc tests. We further attempted to identify ontological pathways modulated during each experimental condition and/or comparison, through integrated qualitative pathway and enrichment analyses. We also explored dynamic longitudinal relationships between the circulating proteome with clinical and hormonal outcomes. 289 and 357 unique proteins were identified per each respective study. Short-term leptin administration during fasting markedly upregulated several proinflammatory molecules, notably CRP and CD14, and downregulated lecithin cholesterol acyltransferase and several immunoglobulin variable chains, in contrast with placebo, which produced minimal changes. Quantitative pathway enrichment further indicated an upregulation of the acute phase response and downregulation of immunoglobulin- and B cell-mediated immunity by leptin. These changes were independent of participant biological sex. In the long study, leptin likewise robustly and persistently upregulated proteins of the acute phase response, and downregulated immunoglobulin-mediated immunity. Leptin also significantly and differentially affected a wide array of proteins related to immune function, defense response, coagulation, and inflammation compared with placebo. These changes were more notable at the 24-week visit, coinciding with the highest measured levels of serum leptin. We further identified distinct co-regulated clusters of proteins and clinical features during leptin administration indicating robust longitudinal correlations between the regulation of immunoglobulins, lipid transport molecules, immune-related molecules, serpins (including cortisol and thyroxine binding globulins), and growth factors, in contrast with placebo, which did not produce similar strong associations. These high-throughput longitudinal results provide unique functional insights into leptin physiology, and pave the way for affinity-based proteomic analyses measuring several thousands of molecules, that will confirm and fully delineate underlying mechanisms. Presentation: 6/2/2024