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Alan T Remaley, Commentary, Clinical Chemistry, Volume 54, Issue 3, 1 March 2008, Pages 610–611, https://doi.org/10.1373/clinchem.2007.101881
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Although apolipoprotein (apo)A-I and apoB are measured by many laboratories as an adjunct to HDL and LDL concentrations, respectively, lipoproteins contain numerous other proteins, some of which have a profound effect on lipoprotein metabolism. ApoE, for example, resides on both antiatherogenic HDL particles and on proatherogenic apoB-containing lipoproteins, thus confounding the usefulness of apoE as a cardiovascular risk marker in unfractionated samples. Nevertheless, apoE has many different roles in lipoprotein metabolism, some of which may account for the macrophage lipid accumulation observed in this interesting case. The best understood function of apoE is that it can serve as a ligand for the cellular uptake of apoB-containing proteins, as well as perhaps HDL, by various receptors. In the absence of a normal form of apoE, there is decreased hepatic clearance of lipoproteins, which leads to their increased oxidation and uptake by macrophage scavenger receptors. ApoE can also help prevent lipid accumulation in cells, particularly in macrophages, which synthesize apoE, by promoting the efflux of excess intracellular cholesterol by the ABCA1 transporter and by other cholesterol efflux mechanisms.
