Metabolism of Very-Low-Density Lipoprotein and Low-Density Lipoprotein Containing Apolipoprotein C-III and Not Other Small Apolipoproteins

Abstract

Objective We aimed to clarify the influence of apolipoprotein C-III (apoCIII) on human apolipoprotein B metabolism. Methods and Results We studied the kinetics of four VLDL, IDL and LDL types containing: (1) OtherApos−CIII−: none of apoCIII, apoAII, apoCI, apoCII or apoE; (2) OtherApos+CIII−: no apoCIII but at least one of the others; (3) OtherApos−CIII+: apoCIII, but not any others; (4) OtherApos+CIII+: apoCIII and at least one other. VLDL and IDL OtherApos−CIII+ and OtherApos−CIII− had similar rates of lipolytic conversion to smaller particles. However, light LDL OtherApos−CIII+ compared to OtherApos−CIII− had much faster conversion to dense LDL, as did light LDL OtherApos+CIII+ compared to OtherApos+CIII−. VLDL and IDL OtherApos−CIII+ had minimal direct removal from circulation, while VLDL and IDL OtherApos+CIII−, rich in apoE, showed fast clearance. Lipoproteins in fraction OtherApos+CIII+ also rich in apoE had very low clearance. Conclusions The results suggest that apoCIII strongly inhibits hepatic uptake of VLDL and IDL overriding the opposite influence of apoE when both are present. The presence of apoCIII on dense VLDL is not associated with slow conversion to IDL, a lipoprotein lipase dependent process; but when on light LDL apoCIII is associated with enhanced conversion to dense LDL, a process involving hepatic lipase.