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It is primarily found in high density lipoprotein (HDL) particles. It serves to prevent the accumulation of cholesterol loaded macrophages which deposit on the arterial wall as foam cells. Its primary function is to activate LCAT within the HDL complex, which catalyzes the esterification of cholesterol. This results in a more soluble cholesterol-HDL complex which increases the cholesterol transport capacity of the HDL particle for subsequent removal by the liver. Apo AI is therefore a convenient marker for assessing the cholesterol clearing capacity of the blood.
Apolipoprotein B (APOB)
It is the primary apolipoprotein of low density lipoproteins (LDL or "bad cholesterol"), which is responsible for carrying cholesterol to tissues. While it is unclear exactly what functional role APOB plays in LDL, it is the primary apolipoprotein component and is absolutely required for its formation. What is clear is that the APOB on the LDL particle acts as a ligand for LDL receptors in various cells throughout the body (i.e. less formally, APOB "unlocks" the doors to cells and thereby delivers cholesterol to them). Through a mechanism that is not fully understood, high levels of APOB can lead to plaques that cause heart disease (atherosclerosis). There is considerable evidence that levels of APOB are a better indicator of heart disease risk than total cholesterol or LDL. However, primarily for practical reasons, cholesterol, and more specifically, LDL-cholesterol, remains the primary lipid target and risk factor for atherosclerosis.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions.