Dissociation of the in vitro transfers of esterified cholesterol and triglyceride between human lipoproteins.

This report describes the detailed time-course of in vitro net mass transfers of esterified cholesterol (EC) and triglyceride (TG) between human plasma lipoproteins incubated in the presence of EC and TG transfer proteins. In incubations containing high density lipoproteins (HDL), very low density lipoproteins (VLDL) and the thiol-group blocker parachloromercuriphenyl sulfonate (PCMPS) (which was added to inhibit EC production), the rate of EC transfer to VLDL was considerably more rapid than that of TG to HDL and equilibrium between the pools of EC was achieved much sooner than was the case for the pools of TG. When VLDL and low density lipoproteins (LDL) were incubated, the presence of PCMPS in the incubation mixture resulted in a marked reduction in the TG transfer to LDL, even though the EC transfer to VLDL was apparently unaffected. The molar ratio of the transfers of EC and TG was also examined in incubations of lipoproteins from a variety of human subjects. In incubations of HDL and VLDL (performed in the absence of PCMPS) there was a large individual variation (sixfold difference) in the molar ratio of the transfers of TG:EC. In incubations of LDL and VLDL from different subjects there was a twofold individual variation in the molar ratio of the transfers of TG:EC. It has been concluded that the net mass transfers of EC and TG between human lipoproteins do not involve a simple molecular exchange of one moiety for the other, as has been suggested previously, but are achieved by processes which are at least partially independent.