*3.1.3 Apolipoprotein B*

Apolipoprotein B (Apo B) is present in the human population in two forms, as apolipoprotein B-48 (Apo B-48) and apolipoprotein B-100 (Apo B-100).

Apo B-48, which is part of the chylomicron, is synthesized in the small intestinal wall. Far more significant is Apo B-100, which is synthesized predominantly in the liver, and is a constituent of VLDL, the intermediate-density lipoprotein (IDL) that circulates for a short time, LDL particles, and the lipoprotein Lp(a). This apoprotein is also characterized by containing certain amounts of carbohydrates (approximately 5% of the total mass), which is chemically classified as glycoproteins [20, 21].

Apo B-100 is secreted primarily from the liver in the form of VLDL particles. By further metabolizing VLDL via IDL, LDL particles are formed that contain exclusively Apo B-100 [4]. The most important role of Apo B-100 is to specifically bind LDL particles to cellular receptors in the liver and other tissues [22].

Given that Apo B-100 is the only apolipoprotein in LDL particles known to have the most heterogeneous effect, it is understandable that an increase in plasma Apo B-100 concentration increases atherogenic risk. Due to the fact that only one Apo B-100 molecule is present in the LDL particle, unlike the amount of cholesterol that can vary in them, the plasma concentration of Apo B-100 is a better indicator of the content of atherogenic lipoprotein particles in the blood than the determination of LDL cholesterol [23].
