Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine

Abstract

We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn-1 FA cleavage compared with sn-2 FA release generated corresponding sn-2 acyl lyso-species as determined by MS analysis. EL failed to release sn-2 FA from rHDLs containing 1-O-1′-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn-1 position contained a nonhydrolyzable alkyl ether linkage.The lack of phospholipase A2 activity of EL and its ability to liberate [14C]FA from [14C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn-1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [14C]phospholipid and [14C]triglyceride upon incubation with 1-palmitoyl-2-[1-14C]linoleoyl-PC-labeled HDL3, indicating the ability of EL to supply cells with unsaturated FAs.

Keywords

• phospholipases
• lysophospholipases
• phospholipids
• polyunsaturated fatty acid
• reconstituted high density lipoprotein