THE EFFECT OF APOLIPOPROTEIN A ON INVITRO APOLIPOPROTEIN C BINDING AND INVIVO REMOVAL OF ARTIFICIAL TRIACYLGLYCEROL-RICH PARTICLES

Although the presence of apolipoprotein A on the surface of chylomicrons and its exchange for apolipoprotein C in the mesenteric lymph is known, the functional role of apolipoprotein A in triacylglycerol transport was not elucidated. Mimicking the in vivo situation, artificial triacylglycerol rich particles (TGRP) with which apolipoprotein Al had been associated, were incubated with high-density lipoproteins (HDL). Apo Al-TGRP bound approximately twice as much apolipoproteinC from HDL as nonprotein-containing TGRP, losing 75% of the apolipoprotein Al originally present. To test whether an increased apolipoprotein C binding in vitro implicated an increased removal rate in vivo, boluses of apolipoprotein Al preincubated and control TGRP were given i.v. to 6 hypertriacylglycerolemic patients. The fractional catabolic rate was 35% (range 6-65%) higher for apolipoprotein Al preincubated TGRP than for control TGRP. In accordance with the in vitro incubations, the molar ratio of apolipoprotein C to phospholipid on TGRP reisolated 30 min after injection was 39% (range 12-115%) higher for apo Al triacylglycerol rich particles (TRP) than for control TGRP. The maximal removal capacity of apo Al-TRP, tested in 1 patient by constant infusion, was increased 53% as compared to control TGRP. The function of apolipoprotein Al in triacylglycerol transport may be to enhance apolipoprotein C binding to chylomicrons, which are comparable to TRP and in doing so to enhance their removal from the plasma compartment.