HDL, stress ossidativo e patologie neurodegenerative: ruolo dell'enzima antiossidante paraoxonasi

Oxidative stress plays a role in the molecular mechanisms of neurodegenerative diseases such as Alzheimer's disease (AD). At cerebral level, AD is characterized by presence of senile plaques constituted by β amyloid (Aβ) peptide. In previous studies it was shown that patients with AD have high plasma levels of oxidized low-density lipoproteins (ox-LDL). In addition, less activity of the enzyme paraoxonase-1 (PON1) was noted. PON1 associated with HDL is the enzyme responsible of anti-inflammatory and antioxidant activity. Aim of thesis was to investigate the functional alterations of HDL in AD patients. Therefore the activity of paraoxonase-1 was evaluated. Furthermore, using microvascular endothelial cells (HMEC), the ability of HDL, isolated from control plasma and AD patients, to protect against Aβ peptide toxicity was evaluated. Results show that mean value of paroxonase activity of PON1 is about a third of that observed in controls (293.6 ± 49.8 U / mL vs 100.3 ± 30.9 U / mL, p <0.001). In AD patients and control's serum were also studied PON1 levels, using Western blot method. PON1 levels of AD patients are significantly lower than those observed in controls. It is interesting to note that the reduced activity of PON1 in AD is observed in the absence of changes in plasma HDL levels compared to controls. Using microvascular endothelial cells (HMEC), the ability of HDL, isolated from controls plasma and AD patients, to protect against toxicity of Aβ peptide was evaluated. Research has shown that Aβ (peptide 1-40) at 20 μM concentration induces a toxic effect by reducing the viability of HMECs. Incubation in presence of HDL isolated from healthy subjects was able to protect cells from toxicity peptide. The results obtained in this thesis have shown that plasma-isolated HDL of Alzheimer's patients are significantly less efficient to protect cells from Aβ-induced damage. Data suggest that the increase in peroxidation products and reduction of PON1 enzyme activity observed in those AD affected make HDL dysfunctional.