Increasing evidence suggests that food ingested polyphenols can have beneficial effects in neuronal protection acting against oxidative stress and inflammatory injury. Moreover, polyphenols have been reported to promote cognitive functions. Biotransformation of polyphenols is needed to obtain metabolites active in brain and it occurs through their processing by gut microbiota. Polyphenols metabolites could directly act as neurotransmitters crossing the blood-brain barrier or indirectly by modulating the cerebrovascular system. The microbiota-gut-brain axis is considered a neuroendocrine system that acts bidirectionally and plays an important role in stress responses. The metabolites produced by microbiota metabolism can modulate gut bacterial composition and brain biochemistry acting as neurotransmitters in the central nervous system. Gut microbiota composition can be influenced by dietary ingestion of natural bioactive molecules such as probiotics, prebiotics and polyphenol. Microbiota composition can be altered by dietary changes and gastrointestinal dysfunctions are observed in neurodegenerative diseases. In addition, several pieces of evidence support the idea that alterations in gut microbiota and enteric neuroimmune system could contribute to onset and progression of these age-related disorders. The impact of polyphenols on microbiota composition strengthens the idea that maintaining a healthy microbiome by modulating diet is essential for having a healthy brain across the lifespan. Moreover, it is emerging that they could be used as novel therapeutics to prevent brain from neurodegeneration.
Keywords: gut-brain axis; gut-microbiota; metagenomic; neurodegeneration; neurotransmitters; polyphenols; prebiotics; probiotics.