Kinetics of in vitro lipolysis of human very low-density lipoprotein by lipoprotein lipase.

BACKGROUND AND AIM: An initial step in the catabolism of triglyceride-rich lipoprotein involves the hydrolysis of the triglyceride moiety by lipoprotein lipase (LPL). As differences in the lipolytic behaviour of very low-density lipoprotein (VLDL) particles have been observed, it is possible that different VLDL particles have a different affinity to the enzyme, which means that their fate may partially depend on the LPL-mediated hydrolysis of their triglyceride content. Our aim was to determine whether variation in VLDL chemical composition affects their properties as a substrate for LPL. METHODS AND
RESULTS: Isolated VLDL was incubated in vitro with bovine LPL to determine substrate affinity. Under optimal assay conditions, free fatty acids were measured and the kinetic indicators for in vitro triglyceride hydrolysis (Km and Vmax) were calculated. VLDL cholesterol (VLDL-C), VLDL-apoB and the cholesterol/triglyceride ratio were assessed and the triglyceride/protein and triglyceride/apoB ratios were calculated as lipoprotein size estimators. VLDL-C, VLDL-apoB and the VLDL-C/triglyceride ratio positively correlated with Km: r = 0.52, p < 0.01; r = 0.52, p < 0.03; r = 0.69, p < 0.001 respectively. No correlation was found between the VLDL-triglyceride/protein or the VLDL-triglyceride/apoB ratios and Km (r = -0.20, and -0.06 respectively, p = not significant). Of the subjects' anthropometric characteristics, only the waist/hip ratio significantly correlated with Km: r = 0.63, p < 0.01.
CONCLUSIONS: In the present study, we investigated the substrate function of VLDL particles in vitro. Enzyme affinity seems to be associated with cholesterol-triglyceride content or the number of VLDL particles rather than particle size. It may be expected that VLDL with a low cholesterol/triglyceride ratio will be efficiently lypolised by LPL, thus leading to the formation of a smaller particle with atherogenic potential.