The effect of apolipoprotein A on in vitro apolipoprotein C binding and in vivo 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 has not been elucidated. Mimicking the in vivo situation, artificial triacylglycerol rich particles (TGRP) with which apolipoprotein AI had been associated, were incubated with high-density lipoproteins (HDL). It was found that apo AI-TGRP bound approximately twice as much apolipoprotein C from HDL as nonprotein-containing TGRP, losing 75% of the apolipoprotein AI originally present. To test whether an increased apolipoprotein C binding in vitro implicated an increased removal rate in vivo, boluses of apolipoprotein AI preincubated and control TGRP were given intravenously (IV) to six hypertriacylglycerolemic patients. The fractional catabolic rate was 35% (range 6% to 65%) higher for apolipoprotein AI 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 minutes after injection was 39% (range 12% to 115%) higher for apo AI triacylglycerol rich particles (TRP) than for control TGRP. The maximal removal capacity of apo AI-TRP, tested in one patient by constant infusion, was increased 53% as compared to control TGRP. Thus, the function of apolipoprotein AI 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.
D000328:Adult; D000368:Aged; D001054:Apolipoproteins A / Q000302:isolation & purification / Q000502:physiology*; D001056:Apolipoproteins C / Q000378:metabolism*; D002914:Chylomicrons / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005217:Fat Emulsions, Intravenous / Q000378:metabolism; D005260:Female; D006801:Humans; D006951:Hyperlipoproteinemias / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010743:Phospholipids / Q000032:analysis; D014280:Triglycerides / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism
D001054:Apolipoproteins A; D001056:Apolipoproteins C; D002914:Chylomicrons; D005217:Fat Emulsions, Intravenous; D010743:Phospholipids; D014280:Triglycerides