Apolipoprotein CIII bound to apoB-containing lipoproteins is associated with small, dense LDL independent of plasma triglyceride levels in healthy men

Objective: Plasma levels of both apolipoprotein CIII (apoCIII) and small, dense LDL particles are associated with plasma triglyceride (TG) concentrations, and are markers for cardiovascular disease (CVD) risk. We tested whether there is an association of apoCIII with small, dense LDL levels that is independent of plasma TG level. Methods: For study I, concentrations of blood lipids, apolipoproteins, and LDL subfractions (analytical ultracentrifugation, AnUC) were measured in 141 healthy middle-aged males. In study II (n=14), density gradient ultracentrifugation of plasma was performed, and 3 fractions in the LDL density range (1.019-1.063. g/ml) were collected. Results: In study I, plasma levels of apoCIII in apoB-containing lipoproteins (LpB:CIII) were associated positively with concentrations of LDL3 (p<0.001) and LDL4 (p<0.001) and negatively with LDL peak particle size (p<0.05) with adjustment for plasma TG. Stepwise multiple regression analysis showed that LpB:CIII was significantly associated with small, dense LDL (LDL3. +. LDL4) levels after adjusting for age, BMI, plasma levels of TG, apoB, and HDL-cholesterol. In study II, the molar ratio of apoCIII to apoB in the LDL fraction of highest density (1.049-1.064. g/ml) was found to be significantly greater (p<0.001) than that in each of two LDL fractions of lower density (1.033-1.038. g/ml; p<0.001 and 1.038-1.049. g/ml; p<0.001). Conclusions: Increased apoCIII content may contribute to metabolic and pathologic properties of small, dense LDL particles.