What is Apolipoprotein B?
Apolipoprotein B is the main protein component of low-density lipoprotein (LDL or "bad" cholesterol), responsible for transporting cholesterol to tissues.
Apolipoprotein B, or more simply APOB, also constitutes about 40 percent of the protein fraction of very low density lipoproteins (VLDL) and chylomicrons (which carry triglycerides of endogenous and exogenous origin).
Functions in the body
APOB is essential for the assembly, secretion and metabolism of these lipoproteins.
Although the function of apolipoprotein B is still far from being completely clarified, we know that it acts as a ligand for LDL receptors located in numerous cells of the body. In practice, it represents the "key" which, once inserted in the lock of the respective "window" located on the outer surface of the cell, allows the entry of cholesterol.
The high-affinity interaction between the LDLs and the LDL receptor (located on the surface of most of the cells of our organism) occurs through the APOB, which is the physiological ligand and therefore largely responsible for regulating LDL cholesterol levels in the plasma.
Why does it measure itself in blood?
The dosages of apolipoprotein B, together with those of other blood indicators, allow us to quantify the risk of undergoing arteriovenous diseases. There is in fact a clear relationship between high levels of APOB and atherosclerosis, so obvious that the dosage of APOB in the blood represents an indicator of better cardiovascular risk compared to LDL cholesterol (which in turn is more indicative of total cholesterol). Similar to the latter, apolipoprotein B levels can be elevated due to genetic and / or environmental factors (high calorie diet rich in saturated fats and simple sugars, overweight, sedentary lifestyle, etc.).
In the blood we find two isoforms, APOB48, synthesized exclusively from the small intestine, and APOB100, produced in the liver.
Normal values
Normal values Apolipoprotein B in plasma: 35-100 mg / 100 ml
Causes of High APOBs
Increase: pregnancy; hypercholesterolemia; defects in LDL receptors; biliary tract obstruction; nephrotic syndrome.
Decrease: hepatopathies; sepsis; estrogen administration; family deficiency of apolipoprotein B.
Health risks
There is a clear relationship between the concentration of APOB100 in the blood and the number of lipoprotein particles of hepatic origin (VLDL, IDL, LDL), since each of these possesses one, and only one, APOB100 protein.
High levels of APOB100 in the blood are therefore synonymous with a high number of LDL lipoproteins, but do not provide any information on their lipid content and in particular cholesterol (the various particles can have a more or less important load of triglycerides and cholesterol). But then how to explain the association between high levels of APOB100 and increased cardiovascular risk?
The presence of a high number of lipoproteins in the circulatory stream is believed to give rise to competition mechanisms for cellular receptors of APOB100 (LDL-R). Since the number of these "locks" and the respective "windows" is limited, the surplus of "keys" (lipoproteins) in the blood, makes them more susceptible to those phenomena of oxidative and non-oxidative origin, which are the basis of the formation of atheromas. These considerations would explain the relationship between high levels of apolipoprotein B and increased risk of coronary heart disease, as well as the greater reliability of this parameter compared to LDL cholesterol.
The levels of apolipoprotein B are often related to those of apoliporotein A1 (which characterizes HDL cholesterol or "good" cholesterol). The lower this ratio (APO-A1 / APO-B), the greater the cardiovascular risk.
