Transfer of Apolipoproteins between Plasma Lipoproteins and Exogenous Lipid Particles after Repeated Bolus Injections or during a Continuous Infusion of Fat Emulsion

Recent studies on the metabolism of artificial lipid particles in a fat emulsion (exo TG) revealed that exo TG acquires apolipoproteins in vivo and in vitro. In particular, apolipoproteins C-II and C-III (apo C-II and apo C-III) are rapidly transferred from high-density lipoprotein (HDL) to exo TG, and return to HDL after the hydrolysis of exo TG. The present study was undertaken to examine whether the movement of apo C-II and apo C-III between HDL and exo TG is influenced by a prior injection of fat emulsion. Two experiments were undertaken. In experiment 1, six male volunteers received three bolus injections of a fat emulsion at a dose of 0.1 g of TG/kg with intervals of 90 min between injections. In experiment 2, the plasma concentrations of triglycerides were maintained at approximately 500 mg/dl for 160 min by the continuous infusion of exo TG. Levels of apo C-II and apo C-III, and the elimination rate of exo TG were followed in each test. In experiment 1, the movement of apolipoproteins between exo TG and HDL was unchanged between the first, second, and third bolus. The elimination rate of exo TG after the third bolus was higher than that after the first bolus. In experiment 2, after the administration of exo TG, the levels of C apolipoproteins in the fraction of HDL began to decrease, and those in the fraction of very-low-density lipoprotein that contained exo TG began to increse. When the concentrations of triglycerides in plasma reached a plateau, the distribution of C apolipoproteins in the lipoprotein fraction also stabilized. These results indicate that the capacity of exo TG for binding apolipoproteins is not influenced by a prior injection of fat emulsion. Thus, the movement of apolipoproteins between exo TG and HDL appears to be continuous, and HDL can clearly supply newly infused exo TG with apo C-II and apo C-III insofar as a continuous infusion of fat emulsion for 160 min is concerned. (Journal of Parenteral and Enteral Nutrition 14:381-385,1990)