Abstract
Plant polyphenols are a broad group of bioactive compounds characterized by different chemical and structural properties, low bioavailability, and several in vitro biological activities. Among these compounds, lignans (a non-flavonoid polyphenolic class found in plant foods for human nutrition) have been recently studied as potential modulators of the gut–brain axis. In particular, gut bacterial metabolism is able to convert dietary lignans into therapeutically relevant polyphenols (i.e., enterolignans), such as enterolactone and enterodiol. Enterolignans are characterized by various biologic activities, including tissue-specific estrogen receptor activation, together with anti-inflammatory and apoptotic effects. However, variation in enterolignans production by the gut microbiota is strictly related to both bioaccessibility and bioavailability of lignans through the entire gastrointestinal tract. Therefore, in this review, we summarized the most important dietary source of lignans, exploring the interesting interplay between gut metabolites, gut microbiota, and the so-called gut–brain axis.
Plant polyphenols are a broad group of bioactive compounds characterized by different chemical and structural properties, low bioavailability, and several in vitro biological activities. Among these compounds, lignans (a non-flavonoid polyphenolic class found in plant foods for human nutrition) have been recently studied as potential modulators of the gut–brain axis. In particular, gut bacterial metabolism is able to convert dietary lignans into therapeutically relevant polyphenols (i.e., enterolignans), such as enterolactone and enterodiol. Enterolignans are characterized by various biologic activities, including tissue-specific estrogen receptor activation, together with anti-inflammatory and apoptotic effects. However, variation in enterolignans production by the gut microbiota is strictly related to both bioaccessibility and bioavailability of lignans through the entire gastrointestinal tract. Therefore, in this review, we summarized the most important dietary source of lignans, exploring the interesting interplay between gut metabolites, gut microbiota, and the so-called gut–brain axis.
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Key Points
The present review described the potential beneficial effects of lignan intake as related to the modulation of gut microbiota and the possible interactions existing with the so-called “gut–brain” axis. Increasing evidence suggests that food ingested polyphenols can have beneficial effects in neuronal protection, acting against oxidative stress and inflammatory injury. Polyphenols may be useful for chronic intestinal disorders, acting at the intestinal level where they achieve their highest concentration in the human body, interacting with inflammation-related cellular signaling pathways and modulating gut microbiota. Furthermore, they can also provide an interesting strategy to defeat neurological disorders, either by direct mechanisms, involving the reduction of neuroinflammation and the enhancement of memory and cognitive functions, or by indirect mechanisms, implying the modulation of gut microbiota and the reduction of intestinal inflammation. Dietary lignans and their gut metabolites should, therefore, be considered as promising nutraceuticals for preventing chronic disorders. In particular, the regulation of gut microbiota composition using polyphenols (such as lignans) may help to restore gut equilibrium and to set up new therapeutic intervention in neuropathologies. In fact, since brain dysfunctions can be linked with dysbiosis of the gut microbiota, a rebalance in the gut microbiota composition may result in a partial or complete reversion of the diseases. Finally, regarding future research directions, a better understanding of the interplay existing between lignans (mainly when considering the gut metabolites enterolignans) and gut microbiota will provide more insight into their health effects, thus opening new possibilities to develop microbiota-based therapies for treating neuronal disorders.