Impact of phosphatidylcholine liposomes on the compositional changes of VLDL during lipoprotein lipase (LPL)-mediated lipolysis

Abstract

Lipoprotein lipase (LPL)-mediated triacylglycerol (TAG) hydrolysis in very low density lipoprotein (VLDL) is accompanied by the release of surface material containing phospholipids (PL), free cholesterol (FC) and apolipoproteins, E (apoE) and Cs (apoCII, apoCIII). The released molecules are accepted by high density lipoprotein (HDL), and new HDL-sized apoE-containing particles are also generated. A decrease in the number of HDL particles or abnormalities in their structure is associated with unfavourable changes in the features of VLDL remnants. Phosphatidylcholine liposomes (PC-L) can also act as acceptors of surface material components released from lipoproteins. Thus, the aim of this study was to assess the impact of liposomes on compositional changes of VLDL during its LPL-mediated lipolysis. VLDL isolated from human sera was incubated with LPL (LPL:VLDLTAG; 24 μg/ml:90 mg/dl) and/or PC-L (VLDLPL:PC-LPL; 1:30 weight ratio). After incubation (2h, 37 °C) VLDL was separated from other reaction products, and VLDL lipid and apolipoprotein content were analysed. Newly generated HDL-sized apoE-containing lipoproteins were separated by two-dimensional non-denaturing gradient gel electrophoresis (2D-PAGGE). The reaction of VLDL with PC-L in the presence or absence of LPL significantly affected the VLDL composition. The ratio of core (TAG+cholesteryl ester) to surface (PL+FC) lipids in VLDL decreased 1.8-fold with PC-L, 1.2-fold with LPL and 3-fold with PC-L+LPL. The reaction with PC-L and PC-L+LPL caused a 3.7-fold and 3.2-fold decrease of apoCs/apoE average weight ratio, respectively. Compositional changes in VLDL under the influence of PC-L were accompanied by an increase in the efficiency of VLDL lipolysis and the generation of apoE-containing HDL-sized particles, heterogeneous in size (from ∼ 9 to ∼ 18.8 nm) and mobility (γ and preβ). We conclude that PL-rich particles, similarly to HDL, promote the release of surface material components from VLDL during LPL-mediated lipolysis and positively influence VLDL features which can facilitate VLDL metabolism. Such PC-L activity may impact on its antiatherogenic properties.

Keywords: Apolipoprotein C; Apolipoprotein E; Lipoprotein lipase; Phosphatidylcholine liposomes; Very low density lipoprotein.