Apolipoprotein C-II modifications associated with an infusion of artificial lipid particles

Artificial lipid particles used as parenteral nutrition solution do not contain any apolipoproteins when they are infused into the circulation. Despite the absence of apolipoproteins, the metabolism of artificial lipid particles is similar to that of chylomicrons which contain various kinds of apolipoprotein. Of the known apolipoproteins, apolipoprotein C-II (apo C-II) is important in the hydrolysis of triglyceride-rich lipoproteins via involvement in the activation of lipoprotein lipase. Modifications of apo C-II associated with intravenous infusion of a lipid emulsion were investigated in eight patients. Changes in apo C-IIs in high density lipoproteins (HDL), low density lipoproteins (LDL) and very low density lipoproteins (VLDL) together with the plasma level of triglycerides, were quantified before and for 90 min after a bolus injection of a 10% lipid emulsion (1 ml/kg of body weight). Immediately prior to the injection, 54% of the total amount of apo C-II was present in HDL, while 27% was present in VLDL. After 5 to 10 min, the amount of apo C-II in HDL decreased to 29% of the total, while that in VLDL increased to 62%. Subsequently, the amounts of apo C-II in HDL and VLDL began to return to the preinjection levels. These variations in apo C-II were closely correlated with the plasma clearance of triglyceride. The result indicates that the injected lipids are not inert particles during their short intravascular life, but that they acquire apo C-II from HDL.