Preferential cholesteryl ester acceptors among triglyceride-rich lipoproteins during alimentary lipemia in normolipidemic subjects.

Abstract

Triglyceride-rich lipoproteins (TRLs), namely chylomicrons (CMs), VLDL, and their remnants, are implicated in the atherogenic features of postprandial lipemia. In human plasma, cholesteryl ester transfer protein (CETP) mediates the heteroexchange of neutral lipids, ie, triglycerides (TG) and cholesteryl esters (CE), between distinct subpopulations of apoB- and of apoAI-containing lipoproteins. In fasting normolipidemic plasma, CETP plays an antiatherogenic role by promoting preferential CE redistribution from HDL to LDL particles of intermediate subclass with optimal binding affinity for the cellular LDL receptor. While the relative proportions and chemical compositions of donor and acceptor lipoproteins are known to influence CETP activity, elevated levels of TRL present during alimentary lipemia have been proposed to be associated with enhanced CETP activity. To identify the preferential CE acceptor particles among postprandial TRL subfractions, we investigated the effects of a typical Western meal (1200 kcal, 14% protein; 38% carbohydrate; and 48% fat, monounsaturated/polyunsaturated ratio 4:1) on the rates of postprandial CE transfer from HDL to apoB-containing lipoproteins in normolipidemic subjects (n=13). Two hours postprandially, plasma levels of TRL were significantly elevated (140 versus 51 mg/dL at baseline, P=.0001). Total rates of CE transferred (88 +/- 7 microg x h[-1] x mL[-1]) from HDL to apoB-containing lipoproteins were not significantly modified by alimentary lipemia over a period of 8 hours. Quantitatively, LDL accepted 64+/-5 microg CE per hour per milliliter plasma from HDL, whereas CM (Sf>400), VLDL1 (Sf 60 to 400), VLDL2 (Sf 20 to 60), and IDL (Sf 12 to 20) accepted 5+/-3, 16+/-3, 1.4+/-0.3, and 1.5+/-0.2, respectively. Quantitatively, VLDL1 was the major CE acceptor among TRLs (P=.0001); thus, VLDL1, but not CMs, represented the major CE acceptor among TRLs. Qualitatively however, VLDL2 and IDL displayed a higher capacity to accept CE from HDL (51.6+/-4.1 and 46.3+/-2.8 microg CE transferred per hour per milligram lipoprotein, respectively; P<.005) compared with CM, VLDL1, and LDL (12.6+/-2.8, 34.7+/-4.2, and 22.7+/-2.0 microg CE transferred per hour per milligram lipoprotein, respectively). In conclusion, elevated postprandial TRL levels are not associated with enhanced total CE transfer to these particles. Furthermore, the qualitative features of postprandial CE transfer from HDL to CM and VLDL1 were not related to the relative TG content of these particles. The CETP-facilitated enrichment of VLDL1 in CE therefore identifies them as potentially atherogenic particles during the postprandial phase.