Induction of ER Stress-Mediated Apoptosis by the Major Component 5,7,4'-Trimethoxyflavone Isolated from Kaempferia parviflora Tea Infusion

Kaempferia parviflora (KP) is a famous medicinal plant from Thailand, and is a rich source of various kinds of methoxyflavones (MFs). Many kinds of food products such as tea, capsule, and liquor are manufactured from the rhizomes of KP. In this study, KP infusions were prepared with different brewing conditions, and the amounts of three major methoxylflavones, 5,7-dimethoxyflavone (DMF), 5,7,4'-trimethoxyflavone (TMF), and 3,5,7,3',4'-pentamethoxyflavone (PMF), were analyzed. The antiproliferative activities of DMF, TMF, and PMF isolated from the brewed tea samples were evaluated. TMF was discovered to be significantly effective at inhibiting proliferation of SNU-16 human gastric cancer cells in a concentration dependent manner. TMF induced apoptosis, as evidenced by increments of sub-G1 phase, DNA fragmentation, annexin-V/PI staining, the Bax/Bcl-xL ratio, proteolytic activation of caspase-3,-7,-8, and degradation of poly (ADP-ribose) polymerase (PARP) protein. Furthermore, it was found that TMF induced apoptosis via ER stress, verified by an increase in the level of C/EBP homologous protein (CHOP), glucose regulated protein 78 (GRP78), inositol-requiring enzyme 1 α (IRE1α), activating transcription factor-4 (ATF-4), and the splice isoform of X-box-binding protein-1 (XBP-1) mRNA.

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.