title: Ultrasensitive cell-based bioassay for the measurement of global estrogenic activity of flavonoid mixtures revealing additive, restrictive, and enhanced actions in binary and higher order combinations.
abstract: Flavonoids present in food, botanicals, and body fluids occur as complex mixtures, and data on their combinatorial estrogenic effects are sparse. Human cell lines that permanently express estrogen receptor (ER) alpha and ERbeta proteins were developed for the measurement of the global estrogenicity of flavonoids in such complex mixtures. The presence of estrogenic ligands, known and unknown, in these mixtures can be detected by activation of an ER-driven luciferase reporter gene. We also examined the effect of hydroxylation on the estrogenic activities of four common flavonoids-apigenin, kaempferol, luteolin, and quercetin, alone and in combination. An inverse relationship was observed between the number of hydroxyl groups in flavonoids and ERalpha bioactivity. When submaximal doses of apigenin, luteolin, kaempferol, genistein, and estradiol were combined in binary and higher order mixtures, the experimental estrogenic effects matched those obtained by summing effects extrapolated from dose-response curves of individual compounds. The estrogenic activities of mixtures containing quercetin were observed to deviate from additivity, suggesting that it was a partial agonist/antagonist. Our assay reveals superagonistic, additive, and antagonistic ERalpha or ERbeta actions of flavonoids and adds to our understanding of the estrogenic effects of phytoestrogens in complex mixtures.
authors.affiliation: Department of Obstetrics and Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Republic of Singapore.
authors.forename: Shih Peng
authors.initials: SP
authors.lastname: Wong
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Ping
authors.initials: P
authors.lastname: Shen
authors.forename: Yinhan
authors.initials: Y
authors.lastname: Gong
authors.forename: Sook Peng
authors.initials: SP
authors.lastname: Yap
authors.forename: Eu Leong
authors.initials: EL
authors.lastname: Yong
mesh_terms: D004357:Drug Synergism; D004359:Drug Therapy, Combination; D047628:Estrogen Receptor alpha / Q000187:drug effects; D047629:Estrogen Receptor beta / Q000187:drug effects; D004967:Estrogens / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D012680:Sensitivity and Specificity; D013329:Structure-Activity Relationship
chemical_list: D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004967:Estrogens; D005419:Flavonoids