Abstract 318: ApoE Modulates the Kinetics of HDL ApoA-I in Humans

Abstract

Human HDL kinetic studies typically measure total apoA-I turnover, rather than partitioning by HDL size or apolipoprotein content. ApoE has potential roles in HDL metabolism by promoting enlargement and clearance. About 5-10% of plasma HDL apoA-I is associated with apoE. To determine whether apoE modulates the kinetics of apoA-I HDL, we compared the metabolism of apoA-I in HDL that has apoE with apoA-I in HDL that does not have apoE. We recruited 5 participants with low HDL-C (average 39 mg/dl, range 24-48 mg/dl) and BMI between 25-35 kg/m 2 . We gave the participants an intravenous bolus of d3-leucine, and collected blood at 14 time points to 70 hours. HDL was isolated from plasma by anti-apoA-I immunoaffinity chromatography, separated by anti-apoE chromatography into HDL that contain or do not contain apoE, and separated using ND-PAGE into 4 size fractions: alpha-1, alpha-2, alpha-3, and prebeta-1. ApoA-I was purified from the 8 HDL subtypes with SDS-PAGE, hydrolyzed into amino acids, and d3-leucine enrichment was measured by GC-MS. Pool size of apoA-I was determined from the protein bands, adjusted to plasma total apoA-I. We used SAAM-II modeling software to compute apoA-I fractional catabolic rates (FCR) and fluxes for each HDL subtype. The FCRs of apoA-I of HDL size fractions that contain apoE were about 2.5 to 5 times faster than that of apoA-I of the corresponding HDL size that does not contain apoE (table). Driven by the higher FCRs, a substantial amount of apoA-I flux in plasma occurs in apoE-containing HDL, varying from 20-40% among the 4 sizes. In summary, apoA-I HDL with apoE is an important, metabolically unique subspecies of HDL that could account for a substantial minority of total HDL flux in plasma.