Higher Levels of Oxidized Low Density Lipoproteins in Alzheimer's Disease Patients: Roles for Platelet Activating Factor Acetyl Hydrolase and Paraoxonase-1

Alzheimer's disease (AD) is associated with oxidative damage of low density lipoproteins (ox-LDL). In order to investigate whether higher levels of ox-LDL are related to alterations of the activity of enzymes involved in lipid metabolism, we studied the activity of paraoxonase-1 (PON1) and platelet activating factor acetylhydrolase (PAF-AH) in AD patients and the relationship between biochemical markers and severity of the disease. Levels of ox-LDL, PON1 (paraoxonase, arylesterase, and lactonase activities), and PAF-AH activity were evaluated in plasma from 49 patients affected by AD and from 34 control subjects matched for gender and age. Our results demonstrated alterations in the activities of PON1 and PAF-AH in AD patients compared to controls and showed, for the first time, a relationship between the activities of these enzymes, ox-LDL levels, and severity of the disease. A significant negative correlation was observed between the ratio PON1/PAF-AH and ox-LDL. Whatever the causes that contribute to a systemic oxidative stress in AD, our results have shown that AD patients exhibit higher PAF-AH activity than control subjects and higher ox-LDL. This phenomenon, in combination with diminished PON1 in these patients and, consequently, the relatively lower ratio PON1/PAF-AH activity, could contribute to inflammation and oxidative stress of plasma lipoproteins.