What does ApoB have to do with heart disease?

ApoB commonly refers to the liver-derived apolipoprotein B-100 protein which is embedded in every circulating fatty molecule aside from HDL-C, although it can also refer to the small intestine-derived apolipoprotein B-48 protein found in some chylomicrons, or both.^[1] These non-HDL fat molecules — VLDL-C, LDL-C, IDL-C, remnant particles, LP(a), and chylomicrons — are contributors to atherosclerosis^[2]. ApoB is the protein of lipoprotein cholesterol molecules, which binds to the LDL receptor and allows the fats in cholesterol particles to be taken up by tissues. Because the conventional risk marker for heart disease, LDL-C, is usually a calculated measure of blood concentration that cannot tell you the total number of particles nor the density of individual particles — key factors in cholesterol particle’s ability to do damage — and because there is exactly one ApoB per lipoprotein molecule, ApoB is emerging as a marker of cardiovascular disease risk that provides added detail when LDL-C is insufficient.^[1][3]