Oleuropein aglycon relieves memory impairments, induces brain autophagy and reduces Aß load in the TgCRND8 mouse model of Alzheimer’s Disease

Oleuropein aglycon relieves memory impairments, induces brain autophagy and reduces Aß load in the TgCRND8 mouse model of Alzheimer’s Disease . C Grossi1, S Ambrosini1, T Ed Dami1, S Rigacci0,2, M Stefani0,2, F Casamenti1 1University of Florence, Department of Pharmacology M.A. Mancini, Viale Pieraccini 6, 50139, Florence, Italy, 2University of Florence, Department of Biochemical Sciences, Viale Morgagni 50, 50134, Florence, Italy Autophagy is a lysosomal degradation process that clears long-lived proteins and organelles from the cytoplasm. Extensive autophagic-lysosomal dysfunction in Alzheimer’s disease (AD) brain contributes to the pathogenesis and enhancing autophagy may represent an innovative therapeutic strategy. Several studies have reported that adherence to the Mediterranean diet (MeDi), rich in unsaturated fatty acids, in polyphenols, vitamins and antioxidants, is associated with a reduced AD risk and the beneficial effects of MeDi may be the result of the association of some individual and non-identified food components and high consumption of olive oil. In this study we have investigated the protective effects of the main polyphenol found in extra virgin olive oil, Oleuropein aglycon (OLE) against Aβ- induced toxicity in the TgCRND8 (Tg) mouse model of amyloid deposition. Double TgCRND8 mice of 3, 6 and 12 months of age, representing an early, intermediate and late stage of amyloid deposition, respectively, were fed for 8 weeks with a 5% fat diet (10 g per mouse/day) containing OLE (50 mg/kg of diet) to examine in vivo the effect of the polyphenol on brain pathology and behavioural impairments. The control mice, Tg and wild type (wt), were fed with the diet not supplemented with OLE. For each group: n=8-10 mice. OLE-administered Tg mice of all ages got significantly better scores (P<0.05, One-way-ANOVA + Bonferroni’s post comparison test) in the context-dependent novel object recognition test, increased their body weight and displayed a better general condition with respect to their littermate controls. In the 3-month-old Tg mice, OLE administration robustly prevents Aß deposition as demonstrated by the significant reduction (P<0.001, Two-tailed Student’s t- test) in the Aβ plaque load within the motor cortex (number = -87% and total area = -75%) and the hippocampus (number = -90% and total area= -80%), markedly reduced the presence of dense-cored Aß plaques in 6- (minimum plaque area:- 50%) and 12-month-old Tg mice. Thioflavin S and OC staining revealed substantial differences in plaques morphology between OLE-administered and control Tg mice. In particular, in the brain of 12-month-old OLE-administered Tg mice several radiating plaques with ribbon-like/diffuse cores and numerous fluffy deposits were detected. OLE treatment decreased the neuroinflammatory reaction mediated by astrocytes while increased microglial/macrophage activation in the 3 age Tg groups, both in the cortex and hippocampus. Interestingly, OLE administration to Tg mice resulted, in the 3 age groups, in marked cortical induction of the autophagic/lysosomal machinery as demonstrated by increased protein levels and immunoreactivities of three essential components of the autophagic pathway Beclin 1, LC3 and p62 and of the lysosomal cysteine protease Cathepsin B. OLE administration resulted in autophagy induction in wt mice too. Overall, our results provide a strong evidence of autophagy induction as a key player of the neuroprotective and beneficial effects of the MeDi and indicate that dietary supplementation with OLE may be prophylactic for AD or, at least, suitable to delay the occurrence and to reduce the severity of its symptoms. Supported by Salute 2009 Regione Toscana, Ente CRF, PRIN 2008