Platelet-activating factor acetylhydrolase is mainly associated with electronegative low-density lipoprotein subfraction.

Background: Electronegative LDL [LDL(-)], a modified subfraction of LDL present in plasma, induces the release of interleukin-8 and monocyte chemotactic protein-1 from cultured endothelial cells.

Methods And Results: We demonstrate that platelet-activating factor acetylhydrolase (PAF-AH) is mainly associated with LDL(-). LDL(-) had 5-fold higher PAF-AH activity than the nonelectronegative LDL subfraction [LDL(+)] in both normolipemic and familial hypercholesterolemic subjects. Western blot analysis after SDS-PAGE confirmed these results, because a single band of 44 kDa corresponding to PAF-AH appeared in LDL(-) but not in LDL(+). Nondenaturing polyacrylamide gradient gel electrophoresis demonstrated that PAF-AH was bound to LDL(-) regardless of LDL size. In accordance with the above findings, nonesterified fatty acids, a cleavage product of PAF-AH, were increased in LDL(-) compared with LDL(+).

Conclusions: The high PAF-AH activity observed in LDL(-) could be related to the proinflammatory activity of these lipoproteins toward cultured endothelial cells.