TRIGLYCERIDE-ENRICHMENT OF HIGH-DENSITY-LIPOPROTEINS ENHANCES THEIR REMODELING BY PHOSPHOLIPID TRANSFER PROTEIN

Phospholipid transfer protein (PLTP) converts high density lipoprotein s (HDL) to larger and smaller particles during incubation in vitro. Th e present study shows that these conversions are enhanced in triglycer ide (TG)-enriched HDL. When pig HDL were enriched with TG by incubatio n with cholesteryl ester transfer protein (CETP) and very low density lipoproteins, the TG/apoA-I molar ratio increased from 0.7/1 to 11.4/1 and the diameter increased from 9.0 to 9.5 nm. When unmodified pig HD L were incubated with PLTP, the diameter increased from 9.0 to 9.5 nm. Incubation of the TG-enriched pig HDL with PLTP generated larger (13. 0 nm) and smaller (7.5 nm) particles. The composition of the large par ticles was comparable to the non-incubated, TG-enriched HDL. The small particles contained only phospholipids and apolipoprotein (apo) A-I. Studies were also carried out with spherical, reconstituted HDL (rHDL) containing only cholesteryl esters in their core. When the rHDL were enriched with TG by incubation with Intralipid and CETP, the diameter increased from 9.0 to 9.2 nm and the TG/apoA-I molar ratio became 5.7/ 1. When unmodified r-HDL were incubated with PLTP, the diameter of 15% of the particles increased to 11.0 nm, 18% decreased to 7.6 nm, and 6 7% were unchanged. When the TG-enriched rHDL were incubated with PLTP, the diameter of 62% of the particles increased to 11.4 nm, 26% decrea sed to 7.6 nm, and 12% did not change. Preincubation with Intralipid a lone or CETP alone did not enrich the rHDL with TG or enhance the size changes. These results show that the TG content of HDL has a major in fluence on PLTP-mediated size changes.