HUMAN TRIACYLGLYCEROL-RICH LIPOPROTEIN SUBFRACTIONS AS SUBSTRATES FOR LIPOPROTEIN-LIPASE

In order to test the hypothesis that lipoprotein lipase (LPL) acts preferentially on larger lipoprotein particles, we determined the susceptibility of triacylglycerol-rich lipoprotein (TRL) subfractions to hydrolysis by LPL in vitro. Chylomicrons (S-f > 400), very low density lipoproteins (VLDL)(1) (S-f 60-400) and VLDL(2) (S-f 20-60) were isolated from six subjects with a range of plasma-triacylglycerol (TAG) concentrations following an overnight fast and for up to 6 h after the consumption of a mixed meal (41% fat). The percent of TRL-TAG hydrolysed by LPL in subfractions isolated following overnight fast was VLDL(1) > VLDL(2) (46.8 +/- 10.2 vs. 25.9 +/- 7.4%, P = 0.006) and 3 h after the meal it was chylomicrons > VLDL(1) > VLDL(2) (81.0 +/- 12.6 vs. 52.8 +/- 10.2 vs, 27.7 +/- 6.2%, chylomicrons vs. VLDL(1) and VLDL(1) vs, VLDL(2), both P less than or equal to 0.005). The percent of VLDL(1)-TAG hydrolysed increased both within and between subjects as VLDL(1)-TAG concentrations increased. This relationship could be explained by the positive correlation observed between VLDL(1)-TAG and VLDL(1)-TAG:apolipoprotein B. In conclusion, increasing the size and TAG content of a lipoprotein particle increases its susceptibility to hydrolysis by LPL.