NEUTRAL LIPID MASS-TRANSFER AMONG LIPOPROTEINS IN PLASMA FROM NORMOLIPIDEMIC SUBJECTS IS NOT AN EQUIMOLAR HETEROEXCHANGE

To further characterize the cholesteryl ester transfer protein (CETP)- mediated distribution of neutral lipids that occurs among lipoproteins in plasma, the net mass transfer of core lipids between donor and acc eptor lipoproteins in intact plasma was measured in ten healthy normol ipidemic subjects. The rate of loss of cholesteryl ester (CE) from hig h density lipoprotein-3 (HDL(3)) (19.5 +/- 8.8 nmol/ml per h) was line ar and increased significantly (P < 0.01) during the 6-h incubation. A pproximately 50% of the CE transferred from HDL(3) (118.7 +/- 54.3 nmo l/ml) went to very low density lipoprotein (VLDL); the remainder was d istributed to low density lipoprotein (LDL) (-30%) and HDL(2) (-20%). The rate of loss of triglyceride (TG) from VLDL (14.5 +/- 6.6 nmol/ml per h) to the HDL subfractions and LDL also was linear and increased s ignificantly with time (P ( 0.01). About 50% of the TG mass lose from VLDL (85.2 +/- 38.4 nmol/ml) was transferred to LDL and the remainder was recovered in HDL (-10%) and HDL(3) (-40%). As the number of nmoles of CE lost from HDLs was almost three times greater than the nmoles o f TG it acquired, these findings indicate that the exchange of cor lip ids in plasma that result from the interaction between CETP-VLDL-HDL(3 ) is not equimolar. Even in the absence of VLDL, HDL(3) continued to d onate CE to LDL and HDL(2) to almost the same degree as in intact plas ma (plasma minus VLDL: 17.5 +/- 5.9 nmol/ml per h vs. intact plasma: 2 0.2 +/- 7.5 nmol/ml per h) without accepting any TG. Our findings demo nstrate that independent pathways exist for the transfer of CE and TG among the plasma lipoproteins and, contrary to what is generally belie ved, a heteroexchange of TG for CE during cholesteryl ester transfer i s not obligatory.