In Vitro Reciprocal Exchange of Apoproteins and Nonpolar Lipids Between Human High Density Lipoproteins and an Artificial Triglyceride-phospholipid Emulsion (Intralipid)

To determine the nature of lipid and apoprotein exchange between human high density lipoproteins (HDL) and Intralipid particles of Sf greater than 400 (ILIP) we have studied their in vitro interaction during incubation in aqueous buffer and in lipoprotein-deficient serum (LPDS). We found that ILIP acquires apo A-I, apo A-IV and apo E from LPDS, and that this uptake is inhibited by the presence of HDL, which readily donate C-apoproteins to the ILIP surface. In the absence of LPDS exchange of only polar lipids occurred between ILIP and HDL, with HDL gaining phospholipid from, and donating free cholesterol to this fat emulsion. In the presence of LPDS the exchange of nonpolar lipids occurred between the two particles: in the case of HDL, cholesteryl ester content decreased, accompanied by an increase in triglyceride, causing a decrease in the hydrated density of the lipoprotein and an increase in its molecular weight; in the case of ILIP, reciprocal changes in lipid content were seen as a loss of triglyceride and the appearance of cholesteryl esters. When compared to literature data, our findings indicate that Intralipid Sf greater than 400 particles exhibit an in vitro behavior which is remarkably similar to that of nascent chylomicrons with respect to the exchange of A- and C-apoproteins and surface polar lipids with HDL. We postulate that since ILIP and HDL can participate in a LPDS-dependent exchange of non-polar core lipids, that this process may occur when this fat emulsion is administered in vivo.