Effects of Supplementation with Probiotics in Experimental Models of Alzheimer's Disease: A Systematic Review of Animal Experiments

Background: Conditions along the brain-gut-microbiota (BGM) axis can significantly contribute to the pathogenesis of Alzheimer's disease (AD). Evidence from animal studies indicates a role of probiotics in regulating mood, cognition, and stress response via the BGM axis. However, the effect of probiotics on AD needs to be better clarified in preclinical and clinical studies. Methods: We prepared this systematic review according to PRISMA. PubMed, Web of Science, Embase, and Virtual Health Library (VHL) were searched for original articles concerning the effects of probiotics in experimental AD. Results: Results were presented as a narrative synthesis according to the Synthesis Without Metaanalysis (SWiM) Guideline. Seventeen studies met the inclusion criteria. The results showed significant effects in the experimental models of AD treated with probiotics alone or in mixture due to expressive improvements in cognitive tests. Conclusion: Furthermore, in most of the included studies, it was possible to observe a reduction in inflammatory processes, an increase in the concentration of peptide hormones, insulin homeostasis in the brain, increased antioxidant enzymes, and a decrease in beta-amyloid deposition and tau hyperphosphorylation. Supplementation of probiotics seems to improve performance in cognitive tests and increase the concentration of substances capable of delaying the neurodegenerative process of AD in experimental models.