Copper-catalyzed oxidation mediates PAF formation in human LDL subspecies. Protective role of PAF:acetylhydrolase in dense LDL.
Free radical-mediated oxidation of cholesterol-rich LDL plays a key role in atherogenesis and involves the formation of oxidized phospholipids with proinflammatory biological activity. We evaluated the production of platelet-activating factor (PAF), a potent inflammatory mediator, in human LDL subspecies on copper-initiated oxidation (4 mumol/L CuCl2, 80 micrograms/mL for hours at 37 degrees C). PAF formation was determined by biological assay of HPLC-purified lipid extracts of copper-oxidized lipoproteins; chemical identity was confirmed by gas chromatographic and mass spectrometric analyses. PAF, characterized as the C16:0 molecular species, was preferentially produced in intermediate LDL (d = 1.029 to 1.039 g/mL) (8.6 +/- 5.7 pmol PAF/3 h per mg LDL protein) and light LDL (d = 1.019 to 1.029 g/mL), but was absent from dense LDL particles (d = 1.050 to 1.063 g/mL). As PAF:acetylhydrolase inactivates PAF and oxidized forms of phosphatidylcholine, we evaluated the relationship of lipoprotein-associated PAF:acetylhydrolase to PAF formation. We confirmed that PAF:acetylhydrolase activity was elevated in native, dense LDL (41.5 +/- 9.5 nmol/min per mg protein) but low in LDL subspecies of light and intermediate density (d 1.020 to 1.039 g/mL) (3.5 +/- 1.6 nmol/min per mg protein) [Tselepis et al, Arterioscler Thromb Vasc Biol. 1995;15:1764-1773]. On copper-mediated oxidation for 3 hours at 37 degrees C, dense LDL particles conserved 20 +/- 14% of their initial enzymatic activity; in contrast, PAF:acetylhydrolase activity was abolished in light and intermediate LDL subspecies. Clearly, the elevated PAF:acetylhydrolase activity of dense LDL efficiently diminishes the potential inflammatory role of endogenously formed PAF; nonetheless, formation of proatherogenic lysophospholipids results. In contrast, LDL particles of the light and intermediate subclasses can accumulate PAF on oxidative modification.
Tsoukatos
D C
DC
Department of Chemistry, University of Ioannina, Greece.
Arborati
M
M
Liapikos
T
T
Clay
K L
KL
Murphy
R C
RC
Chapman
M J
MJ
Ninio
E
E
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D002384:Catalysis; D003300:Copper; D005260:Female; D005609:Free Radicals; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D010084:Oxidation-Reduction; D010741:Phospholipases A / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000031:analogs & derivatives / Q000378:metabolism*
D005609:Free Radicals; D008077:Lipoproteins, LDL; C029271:O-deacetyl platelet activating factor; D010972:Platelet Activating Factor; D003300:Copper; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase