Flavonols enhanced production of anti-inflammatory substance(s) by Bifidobacterium adolescentis: prebiotic actions of galangin, quercetin, and fisetin.

The gut microbiota is capable of the bioconversion of flavonoids whereas influences of probiotic anaerobes on the bioactivities of flavonoids and vice versa are still unclear. Here, we investigated functional interactions with respect to the anti-inflammatory activity between flavonols and probiotic bacteria. Ten enteric (6 probiotic and 4 indigenous) bacteria were incubated with flavonols (galangin, kaempferol, quercetin, myricetin, and fisetin) under anaerobic conditions, and the supernatants were assessed for their effects on nitric oxide (NO) production in lipopolysaccaride-stimulated RAW264 cells. Although the conditioned medium from the flavonol mono-culture and almost all of the tested co-cultures failed to inhibit NO production, the medium from the Bifidobacterium adolescentis/flavonols (galangin, quercetin, and fisetin) co-culture highly suppressed NO production. This activity increased during the 1-6 H incubation in a time-dependent manner and was not observed in the co-culture using heat-inactivated B. adolescentis. Interestingly, when the B. adolescentis cell number was increased, the supernatant from the mono-culture of the bacteria showed NO suppression, suggesting that B. adolescentis may produce NO suppressant(s), and flavonols may have a promoting effect. These findings indicate that flavonols have a prebiotic-like effect on the anti-inflammatory activity of B. adolescentis.