Relationship of Apolipoprotein B Levels to the Number of Risk Factors for Metabolic Syndrome

Low-density lipoprotein cholesterol (LDL-C) is the primary target of lipid-lowering therapy. However, all lipoproteins containing apolipoprotein B (apo B) appear to be atherogenic. Preferred targets of therapy therefore may include either the cholesterol in all apo B-containing lipoproteins (non-high-density lipoprotein cholesterol [non-HDL-C]) or total apo B itself. Apo B can be measured by three methods: chemically, by nuclear magnetic resonance (NMR), and by immunoassay. This study compares the first two methods as a function of the number of metabolic risk factors in patients with metabolic syndrome. Plasma lipid, lipoprotein cholesterol, and apo B levels were measured in 274 adults with varying numbers of metabolic syndrome components. Low-density lipoprotein (LDL) particle sizes were measured by gel electrophoresis and by NMR. Total apo B was estimated chemically and by conversion of NMR lipoprotein particle number, assuming one apo B molecule per lipoprotein particle. As the number of metabolic syndrome components increased, apo B rose by both chemical and NMR methods, but by chemical methods, increases were in the triglyceride-rich fraction, whereas by NMR, they were in LDL. The correlation between total apo B measured by the two methods was only moderate (r = .73). Further, non-HDL-C was more highly correlated with total apo B measured chemically than either LDL-C or total apo B by NMR. Non-HDL-C correlates highly with total apo B in patients with metabolic syndrome and had advantages as a target of therapy over LDL-C or NMR apo B.