Demethylation of Polymethoxyflavones by Human Gut Bacterium, Blautia sp. MRG-PMF1

Polymethoxyflavones (PMFs) were biotransformed to various demethylated metabolites in the human intestine by the PMF-metabolizing bacterium, Blautia sp. MRG-PMF1. Because the newly formed metabolites can have different biological activities, the pathways and regioselectivity of PMF bioconversion were investigated. Using an anaerobic in vitro study, 12 PMFs, 5,7-dimethoxyflavone (5,7-DMF), 5-hydroxy-7-methoxyflavone (5-OH-7-MF), 3,5,7-trimethoxyflavone (3,5,7-TMF), 5-hydroxy-3,7-dimethoxyflavone (5-OH-3,7-DMF), 5,7,4′-trimethoxyflavone (5,7,4′-TMF), 5-hydroxy-7,4′-dimethoxyflavone (5-OH-7,4′-DMF), 3,5,7,4′-tetramethoxyflavone (3,5,7,4′-TMF), 5-hydroxy-3,7,4′-trimethoxyflavone (5-OH-3,7,4′-TMF), 5,7,3′,4′-tetramethoxyflavone (5,7,3′,4′-TMF), 3,5,7,3′,4′-pentamethoxyflavone (3,5,7,3′,4′-PMF), 5-hydroxy-3,7,3′,4′-tetramethoxyflavone (5-OH-3,7,3′,4′-TMF), and 5,3′-dihydroxy-3,7,4′-trimethoxyflavone (5,3′-diOH-3,7,4′-TMF), were converted to chrysin, apigenin, galangin, kaempferol, luteolin, and quercetin after complete demethylation. The time-course monitoring of PMF biotransformations elucidated bioconversion pathways, including the identification of metabolic intermediates. As a robust flavonoid demethylase, regioselectivity of PMF demethylation generally followed the order C-7 > C-4′ ≈ C-3′ > C-5 > C-3. PMF demethylase in the MRG-PMF1 strain was suggested as a Co-corrinoid methyltransferase system, and this was supported by the experiments utilizing other methyl aryl ether substrates and inhibitors.