A novel Mediterranean diet-inspired supplement reduces hippocampal amyloid deposits and microglial activation through the modulation of the microbiota gut-brain axis in 5xFAD mice

Background: Alzheimer's disease (AD) is projected to increase in prevalence, heightening the need for strategies to alleviate its neuropathological burden. The bioactive constituents of a Mediterranean-style diet are well-recognised for their neuroprotective properties. Due to their capacity to alter the gut microbiome composition, these benefits may involve modulation of the microbiota-gut-brain axis. In this study, we investigated whether a novel supplement enriched with key Mediterranean diet-derived bioactives (Neurosyn240) could reduce amyloid deposition and microglial activation in 5xFAD mice, a transgenic model of AD, through microbiota-mediated mechanisms. Methods: Male and female 5xFAD transgenic mice (n = 16 per sex) were randomly assigned to receive either a standard control diet or a diet supplemented with Neurosyn240 for 12 weeks. Employing a multi-omics approach, gut microbiota composition was profiled using 16S rRNA ampliconsequencing, serum metabolites were quantified via targeted metabolomics, and hippocampal gene expression was analysed through qPCR and RNA sequencing. Neuropathological markers, including amyloid-β deposition and microglial activation, were evaluated using immunofluorescence staining. Statistical analyses were performed using two-way ANOVA to examine the main effects of diet and sex and their interaction. Results: Neurosyn240 significantly shifted the gut microbiome composition, which was associated with increased circulatory serotonin levels and decreased kynurenine and bile acids (TCA, HDCA, TDCA, CDCA and LCA) concentrations. In the brain, Neurosyn240 consumption led to a significant reduction in hippocampal amyloid deposits and Iba-1 positive microglia (p<0.05), which were associated with decreased LCA and increased serotonin, respectively. Hippocampal RNA sequencing further highlighted the upregulation of genes involved in promoting amyloid beta clearance mechanisms. Conclusions: Together, these findings highlight novel neuroprotective effects of Neurosyn240 in modulating metabolite-mediated pathways of the microbiota-gut-brain axis, accentuating its therapeutic potential against AD progression.