Availability of apolipoprotein CII in relation to the maximal removal capacity for an infused triglyceride emulsion in man.

The aim of this study was to evaluate whether the transfer to triglyceride-rich particles of apolipoprotein CII is a quantitative determinant of triglyceride removal. An emulsion of triglyceride, Intralipid, which resembles chylomicrons in particle size but does not contain apolipoprotein, was infused at a constant rate for 1 hr in ten subjects with plasma triglyceride levels ranging from 40 to 636 mg/dl. During the infusion, samples were taken for measurement of particulate triglyceride by nephelometry and quantification of apolipoprotein content by polyacrylamide gel electrophoresis of reisolated particles. The maximal removal capacity for Intralipid-triglyceride, calculated as the infusion rate minus the linear increase in plasma Intralipid-triglyceride, was inversely related to the basal plasma triglyceride level. The apolipoproteins bound to Intralipid were apo CI, CII, and CIII. Apo A and apo E were not detected. The $\text{CII}\text{CIII}$ ratio was higher in larger triglyceride-rich particles (Intralipid) than in smaller ones (VLDL and HDL). The $\text{CII}\text{CIII}$ ratio in VLDL isolated before infusion was higher than in VLDL isolated 2 min after starting infusion. The amount of apolipoprotein CII bound to infused Intralipid increased in parallel to the increase in triglyceride level, with a constant $\text{CII}\text{TG}$ ratio between 2 and 60 min. The maximal removal capacity for infused Intralipid-triglyceride was not quantitatively related to the CII binding, expressed as $\text{CII}\text{TG}$. It is concluded that (1) the transfer of apolipoprotein CII from HDL, and also from VLDL, to large triglyceriderich emulsion particles entering the circulation occurs within minutes; (2) the availability of apolipoprotein CII for binding to continuously entering Intralipid particles is unlimited during 1 hr; (3) the amount of apolipoprotein CII bound does not control the rate of Intralipid-triglyceride removal from the plasma.