Oral Administration of Probiotic Bacteria Alleviates Tau Phosphorylation, Aβ Accumulation, Microglia Activation, and Memory Loss in 5xFAD Mice.

The gut-brain axis (GBA) plays a significant role in various neurodegenerative disorders, such as Alzheimer's disease (AD), and the gut microbiome (GM) can bidirectionally communicate with the brain through the GBA. Thus, recent evidence indicates that the GM may affect the pathological features and the progression of AD in humans. The aim of our study was to elucidate the impact of probiotics on the pathological features of AD in a 5xFAD model. Probiotics ( Bifidobacterium lactis , Levilactobacillus brevis , and Limosilactobacillus fermentum ) were orally administered in 5xFAD mice to modify the GM composition. Additionally, freeze-dried food containing phosphatidylserine was used as the positive control. Behavioral pathogenesis was assessed through the cross maze and Morris water maze tests. Our findings revealed that probiotic administration resulted in significant improvements in spatial and recognition memories. Furthermore, the neuroprotective effects of probiotics were substantiated by a reduction in amyloid-β accumulation in critical brain regions. Microglial activation in 5xFAD mice was also attenuated by probiotics in the hippocampus and cerebral cortex. Moreover, elevated tau phosphorylation in 5xFAD mice was ameliorated in the probiotics-treated group. The results highlight the potential use of probiotics as a neuroprotective intervention in AD.