The In Vivo Metabolic Pathways of Nobiletin in Mice: The Critical Role of Gut Microbiota

Nobiletin, a major citrus polymethoxyflavone, offers significant health benefits closely related to its metabolism in vivo. However, its metabolic pathways and gut-microbiota-mediated biotransformation remain poorly understood. Herein, conventional mice and antibiotic-treated mice were used to (i) elucidate in vivo metabolic pathways of nobiletin and (ii) establish gut microbial functions in nobiletin biotransformation. Using UPLC-Q-TOF analysis, we identified 19 demethylated metabolites of nobiletin, eight of which were newly discovered. Antibiotic-treated mice showed distinct nobiletin metabolite profiles compared with those of conventional mice. The gut microbiota is critical in producing demethylated metabolites, especially didemethylated and tridemethylated ones. Notably, more than 10 demethylated nobiletins were almost exclusively generated by gut microbiota. Additionally, gut microbiota facilitate the deconjugation of glucuronide and sulfate conjugates of demethylated nobiletin, yielding deconjugated forms with potentially high bioactivity. Overall, this study highlights the essential role of gut microbiota in the biotransformation of nobiletin in vivo.