Dietary flavonoids are known to be metabolized by gut microbiota, and the impact of their metabolites on human health have been widely investigated. Although some species of bacteria capable of metabolizing flavonoids are isolated from intestinal microflora, the role of the bifidobacteria is poorly understood. Bifidobacterium species are a major component of human gut microflora, and beneficial for our health. Prebiotics, such as dietary fiber and oligosaccharides, improve the intestinal environment through the increased proliferation of the bifidobacteria. We have previously found that quercetin, EGCg and several flavonoids enhance in vitro anti-inflammatory activity of Bifidobacteirum adolescentis. Since these flavonoids reduced to a similar extent in both culture medium with and without B. adolescentis, anti-inflammatory molecules may be products from B. adolescentis, but not active metabolites of quercetin by the bacteria. The aim of this study was to investigate functional properties of anti-inflammatory culture supernatant of B. adolescentis with quercetin and its underlying mechanisms. Culture supernatant of B. adolescentis with quercetin decreased the levels of inflammatory mediators in lipopolysaccharide-stimulated RAW264 macrophages, indicating that the biologically active molecule secreted from B. adolescentis may suppress the inflammatory signaling in macrophages. Acetate and lactate, which are major fermented products of bifidobacteria, had little effect on the activated macrophages. Physicochemical analysis of the supernatant was revealed that the active molecule has thermostable, non-phenolic, and acidic properties with molecular weight less than 3 kDa. Quercetin itself but not its degraded compounds occurring during the culture period was needed for inducing the anti-inflammatory activity. The binding level on flavonoid-sensitive strain of B. adolescentis was higher than that of an insensitive strain. Additionally, methylated EGCg was more potent than EGCg. These findings suggest that these flavonoids may interact with the bacterial surface, and then induce the production of a small active molecule.

Flavonoids enhance in vitro anti-inflammatory activity of bifidobacteria by inducing the secretion of a small active molecule

256th National Meeting (2018)

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