LDL Density and Oxidation are Modulated by PON1 Promoter Genotype in Patients with Alzheimer's Disease

Cholesterol metabolism alteration is a hot topic in the field of Alzheimer's disease (AD). However, data on plasma lipoproteins cholesterol distribution and oxidation in AD and their possible genetic determinants are lacking. The paraoxonase-1 (PON1) gene -107C/T promoter polymorphisms have been found associated with AD. One of the fundamental functions of PON1 enzyme is the inhibition of low-density lipoproteins (LDL) oxidation. We therefore evaluated plasma lipoprotein profile and LDL density and oxidation in late-onset AD patients and healthy elderly subjects, without neuroimaging evidence of cerebrovascular lesions and not on lipid-lowering treatment, and their interaction with PON1 -107C/T and apolipoprotein E (APOE) genotypes. Mean plasma total cholesterol and LDL levels were higher in AD than controls (p < 0.05). Lipoproteins cholesterol distribution shifted toward a greater prevalence of smaller, denser LDL (sd-LDL, p < 0.05) only in AD patients with PON1 -107TT genotype, who also showed increased plasma levels of oxidized LDL (ox-LDL, p = 0.02). A significant association was observed between sd-LDL and ox-LDL levels (p < 005) in AD patients. APOE genotype did not modulate lipoprotein distribution. Increased levels of sd-LDL and ox-LDL particles in the AD PON1 TT patients could be explained by the combined effect of an AD-related pro-oxidant milieu and an ineffective PON1 gene polymorphism-related antioxidant capacity. The functional correlate of the association between PON1 -107C/T polymorphism and AD may be the abnormal modulation of LDL oxidation. Ox-LDL may amplify the processes of endothelial injury promoted by vascular amyloid deposition, which represents one of the potential pathways explaining the cross-road between vascular and neurodegenerative pathomechanisms in AD.