CHRONIC ADMINISTRATION OF CHF5074, A NOVEL g-SECRETASE MODULATOR, PREVENTS BRAIN NEURODEGENERATION IN AGED ALZHEIMER’S DISEASE TRANSGENIC MICE

Background: CHF5074, a new gamma-secretase modulator, has beenshown to inhibit brain plaque deposition and attenuate or reverse associated memory deficits in different transgenic mouse models of Alzheimer’s disease. We evaluated the effect of CHF5074 chronic administration on molecular, cellular and anatomical indices of brain atrophy. Methods: Five-month-old Tg2576 mice and their wild-type littermates were treated with CHF5074 in the diet (125 or 375 ppm equivalent to about 20 and 60 mg/Kg/day) or vehicle for 13 months. At the end of the treatment, brain areas were weighed and measured, and the expression of synaptophysin, cyclin A, intracellular APP/Abeta, plaque load, activated microglia were evaluated with immunohistochemistry and quantitative image analysis. Cognitive performance was measured with the object recognition test. Results: Compared to wild-type mice, Tg2576 mice showed a lower body weight gain curve (-26.364.4%, p<0.0001) but a higher brain/ body weight ratio (2.1460.08% vs 1.6660.04%, p< 0.0001). CHF5074 long-term treatment normalized this ratio in Tg2576 mice (2.0460.07% and 1.9660.05% in the low and high dose groups, respectively). Compared to vehicle-treated Tg2576 mice, CHF5074 treatments significantly lowered intraneuronal APP/Abeta stained with 6E10 anti- Abeta (1-16) monoclonal antibody (-33.567.3%, p< 0.01 and -27.164.9%, p< 0.01). Amyloid burden was also reduced significantly by both CHF5074 dose treatments in both cortex (-61.065.1% and -48.268.9%) and hippocampus (-52.369.4% and -64.968.1%). Activated microglia in hippocampus was also significantly reduced by CHF5074 hippocampus (-53.763.8% and -47.764.2%). In transgenic mice there was a significant 41.363.6% reduction compared to wildtype animals in synaptophysin-immunoreactivity in the cerebral cortex and both CHF5074 doses reversed this deficit. Cyclin A immunoreactivity was identified in NeuN-positive cells, which defines mature neurons. The number of CycA-positive cells over the total number of NeuN-positive neurons was counted in layer II-III of the medial cerebral cortex. While in wild-type mice the percentage of neurons expressing CycA was 8.661.5%, we found that 47.863.3% of neurons expressing CycA in Tg2576 mice. Treatment with CHF5074 reduced this value to 17.661.5% (p < 0.01) and 17.861.3% (p< 0.01) in the 20 mg/kg/day and 60 mg/kg/day groups, respectively. CHF5074 dose-dependently reversed object recognition memory deficit in transgenic mice. Conclusions: This study indicated that CHF5074 affects several molecular and cellular neuronal parameters associated to the aging of the Tg2576 mice’s brain. The normalization of the brain volume of the transgenic mice treated with the drug could be related to the reduction of the age-associated neuroinflammation and/or to the marked reduction of the amyloid plaque burde