Proteomic and Kinetic Analyses Reveal Discordant Apolipoprotein Turnover and Support a Revised Model of Human Lipoprotein(a) Metabolism

Lipoprotein(a) [Lp(a)] is a causal risk factor for atherosclerotic cardiovascular disease composed of apolipoprotein(a) [APO(a)] covalently linked to apolipoprotein B100 (APOB). Although plasma Lp(a) concentrations are largely genetically determined, the mechanisms governing Lp(a) metabolism after particle assembly remain poorly understood. We performed a cross sectional, observational study to define the Lp(a) proteome and determine the metabolic behavior of APO(a) and APOB within circulating Lp(a) particles using integrated proteomic, kinetic, and imaging approaches. Sixteen healthy adults underwent stable isotope tracer studies with ²H₃-L-leucine and ²H₅-glycerol. Lp(a) particles were isolated by APO(a)-specific immunoprecipitation for high-resolution liquid chromatography-mass spectrometry and kinetic analyses, and extracellular vesicles (EVs) were characterized by imaging flow cytometry and super-resolution microscopy. Proteomic analysis identified 92 proteins associated with immuno-isolated Lp(a), enriched in pathways related to immunity, coagulation, and atherogenesis. Lp(a)-APO(a) exhibited a mean fractional clearance rate of 0.04 pools/day, whereas Lp(a)-APOB cleared approximately sevenfold faster (0.25 pools/day), independent of plasma Lp(a) concentration or APO(a) isoform size. Both APO(a) and APOB were detected on circulating EVs, suggesting that EVs may contribute to post-secretory Lp(a) particle remodeling. These integrated human studies demonstrate marked discordance between APO(a) and APOB turnover within circulating Lp(a) particles, challenging the prevailing assumption that both apolipoproteins behave as a single metabolic unit after Lp(a) assembly and supporting a revised model of human Lp(a) metabolism.