title: Methylation of quercetin and fisetin, flavonoids widely distributed in edible vegetables, fruits and wine, by human liver.
abstract: The aim of this investigation was to study the methylation of quercetin and fisetin, 2 chemically related flavonoids, in human liver and to this purpose, an assay was set-up to measure the rates of quercetin and fisetin methylation in human liver. The methylation rates (pmol/min/mg) of quercetin and fisetin were measured in 10 liver samples and the mean +/- SD and the median were 170+/-30 and 177 (quercetin) and 183+/-15 and 178 (fisetin). The rates of quercetin and fisetin methylation were not different (p = 0.283). The fold of variation among samples was 2 (quercetin) and 1.3 (fisetin). Methyltransferase towards quercetin and fisetin followed Michaelis-Menten kinetics, and the Km values were 2.6+/-0.3 (quercetin) and 8.6+/-0.7 microM (fisetin, p = 0.009) and the Vmax values were 187+/-20 (quercetin) and 276+/-33 pmol/min/mg (fisetin, p = 0.009). Two, 4 and 8 microl of red Chianti wine added to the incubation mixture reduced the rate of quercetin methylation to 75+/-4%, 65+/-9% and 59+/-9%, respectively, and that of fisetin methylation to 62+/-3%, 51+/-3% and 44+/-4%, respectively. In conclusion, quercetin and fisetin are methylated in human liver and their rates of methylation have a limited variation among subjects.
authors.affiliation: Department of Neuroscience, Section of Pharmacology, Medical School, Cisanello Hospital at University of Pisa, Italy.
authors.forename: C
authors.initials: C
authors.lastname: De Santi
authors.forename: A
authors.initials: A
authors.lastname: Pietrabissa
authors.forename: F
authors.initials: F
authors.lastname: Mosca
authors.forename: G M
authors.initials: GM
authors.lastname: Pacifici
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005419:Flavonoids / Q000378:metabolism*; D044948:Flavonols; D005638:Fruit / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D008745:Methylation; D008875:Middle Aged; D011794:Quercetin / Q000378:metabolism*; D014675:Vegetables / Q000737:chemistry; D014920:Wine
chemical_list: D005419:Flavonoids; D044948:Flavonols; D011794:Quercetin; C017875:fisetin