Apolipoprotein A-I–containing high-density lipoprotein-associated unesterified cholesterol (HDL-FC)

Free cholesterol on apolipoprotein A-I (apoA-I)–containing high-density lipoprotein (HDL) particles is a key intermediate in the reverse cholesterol transport (RCT) pathway, representing the fraction of cholesterol recently mobilized from peripheral tissues. This entity is formed when lipid-poor apoA-I interacts with the ATP-binding cassette transporter A1 (ABCA1) on cells such as macrophages to accept unesterified (free) cholesterol (Rosenson et al., 2016). The resulting nascent HDL particles serve as the primary vehicle for transporting excess cholesterol from atherosclerotic plaques to the liver for excretion (StatPearls, 2023). In clinical development, this complex is not a drug target in the traditional sense but is the functional product of therapies like CSL112, which are reconstituted apoA-I particles designed to enhance cholesterol clearance (Gibson et al., 2024). While increasing these particles was hypothesized to reduce major adverse cardiovascular events (MACE), recent Phase 3 data from the AEGIS-II trial showed no significant reduction in myocardial infarction or stroke (Gibson et al., 2024). Consequently, while it remains a vital biomarker of HDL function, its role as a primary therapeutic focus is currently under re-evaluation (Gibson et al., 2024). The conversion of this free cholesterol into cholesteryl esters by the enzyme LCAT is a subsequent step that matures the HDL particle (Rosenson et al., 2016). Therapeutic strategies targeting this pathway often focus on the infusion of apoA-I mimetics or purified apoA-I to maximize the formation of these cholesterol-accepting particles.

Other names

Free cholesterol on apoA-I-HDLUnesterified cholesterol on high-density lipoproteinApolipoprotein A-I-associated free cholesterolPre-beta HDL cholesterolHDL-associated unesterified cholesterol

Enhancement of cholesterol efflux capacity (CEC) by providing acceptor particles for ABCA1-mediated transport of unesterified cholesterol from peripheral tissues (Gibson et al., 2024).