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Abstract
Oxidized low-density lipoprotein (oxLDL) and oxidized high-density lipoprotein (oxHDL), known as risk factors for cardiovascular disease, have been observed in plasma and atheromatous plaques. In a previous study, the content of oxidized phosphatidylcholine (oxPC) and lysophosphatidylcholine (lysoPC) species stayed constant in isolated in vivo oxLDL but increased in copper-induced oxLDL in vitro. In this study, we prepared synthetic deuterium-labeled 1-palmitoyl lysoPC and palmitoyl-glutaroyl PC (PGPC), a short chain-oxPC to elucidate the metabolic fate of oxPC and lysoPC in oxLDL in the presence of HDL. When LDL preloaded with d13-lysoPC was mixed with HDL, d13-lysoPC was recovered in both the LDL and HDL fractions equally. d13-LysoPC decreased by 50% after 4 h of incubation, while d13-PC increased in both fractions. Diacyl-PC production was abolished by an inhibitor of lecithin-cholesterol acyltransferase (LCAT). When d13-PGPC-preloaded LDL was incubated with HDL, d13-PGPC was transferred to HDL in a dose-dependent manner when both LCAT and lipoprotein-associated phospholipase A2 (Lp-PLA2) were inhibited. Lp-PLA2 in both HDL and LDL was responsible for the hydrolysis of d13-PGPC. These results suggest that short chain-oxPC and lysoPC can transfer between lipoproteins quickly and can be enzymatically converted from oxPC to lysoPC and from lysoPC to diacyl-PC in the presence of HDL.
Highlights
Lipoproteins modified by oxidation, including oxidized low-density lipoprotein and oxidized high-density lipoprotein, are crucial for atherosclerosis development
This in vivo oxidized low-density lipoprotein (oxLDL) had unique characteristics; first, its apoB-100 was modified with oxidized products, including oxidized phosphatidylcholine (oxPC); second, it coeluted with oxidized high-density lipoprotein (oxHDL) indicating that oxLDL could interact with oxHDL particles in this fraction; third, the binding of oxLDL and oxHDL was not covalent but electrostatic
These results suggest that the lipoprotein-associated phospholipase A2 (Lp-Phospholipase A2 (PLA2)) present in both haenbadr lower layer (HDL) and LDL contributes to the hydrolysis of oxPC molecules
Summary
Lipoproteins modified by oxidation, including oxidized low-density lipoprotein (oxLDL) and oxidized high-density lipoprotein (oxHDL), are crucial for atherosclerosis development. At least two types of in vivo oxLDL were separated by anion-exchange column chromatography, one of which was negatively charged particles and increased by three-fold in the plasma obtained from patients with acute myocardial infarction compared to healthy plasma This in vivo oxLDL had unique characteristics; first, its apoB-100 was modified with oxidized products, including oxPC; second, it coeluted with oxHDL indicating that oxLDL could interact with oxHDL particles in this fraction; third, the binding of oxLDL and oxHDL was not covalent but electrostatic. Short chain-oxPC was capable of transferring between lipoproteins and was susceptible to hydrolysis by Lp-PLA2 These observations suggest that the oxPC and lysoPC species can be metabolized by interactions between oxLDL and HDL during the oxidation of LDL in vivo
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