Apolipoprotein B and LDL Transport
Yes, Apolipoprotein B (Apo B) is the major structural protein that carries LDL and other atherogenic lipoproteins in the bloodstream. 1
Structure and Function of Apo B
- Apo B exists in two major isoforms: apoB48 and apoB100, with apoB100 being the form present on LDL particles 2
- Each LDL particle contains exactly one molecule of apoB100, making apoB concentration a direct measure of the number of atherogenic particles in circulation 2
- ApoB is the main structural protein of LDL, triglyceride-rich lipoproteins, and lipoprotein(a), and is crucial for their formation, metabolism, and atherogenic properties 1
Relationship Between Apo B and Atherogenic Lipoproteins
- ApoB is the major apolipoprotein of the atherogenic lipoprotein families: Very Low-Density Lipoprotein (VLDL), Intermediate-Density Lipoprotein (IDL), and Low-Density Lipoprotein (LDL) 3
- The concentration of apoB provides a good estimate of the total number of these potentially atherogenic particles in plasma 3
- ApoB assembles the precursor of LDL (VLDL) in the liver, starting with formation of a primordial particle that is eventually converted to VLDL and then to LDL 4
Clinical Significance of Apo B
- ApoB mediates the interaction between LDL and the arterial wall, with two specific regions in apoB involved in this binding 4
- LDL enters the artery wall by transcytosis and, in vulnerable regions, is retained in the subendothelial space by binding to proteoglycans via specific sites on apoB 1
- The European Society of Cardiology/European Atherosclerosis Society has stated that apoB is a more accurate marker of cardiovascular risk than LDL-C and non-HDL-C 5
Advantages of Apo B Measurement
- ApoB measurement does not require fasting conditions and is not sensitive to moderately high triglyceride levels 3, 6
- Good immunochemical methods are available for apoB testing, which can be easily run on conventional autoanalyzers with good analytical performance 6
- ApoB provides a direct measure of the number of atherogenic particles present in circulation, with one ApoB molecule present on each potentially atherogenic lipoprotein particle 7
Limitations of Apo B as a Target
- Despite its advantages, apoB has not been evaluated as a primary treatment target in statin trials, though several post-hoc analyses suggest it may be a better treatment target than LDL-C 3
- Most risk estimation systems and virtually all drug trials are based on total cholesterol and LDL-C rather than apoB 3
- ApoB measurement carries extra expense compared to standard lipid panels, which may limit its widespread adoption 7
Recent Evidence Supporting Apo B
- Recent studies from the UK Biobank suggest that apoB is a more accurate marker for cardiovascular risk than LDL particle number when these measurements are discordant 8
- Risk was elevated at as little as 2% discordance between apoB and LDL particle number, suggesting that even modest mismatches may be clinically relevant 8
- Multiple studies have shown that apoB is superior to LDL cholesterol in predicting cardiovascular disease events 7