Activation of transgenic estrogen receptor-beta by selected phytoestrogens in a stably transduced rat serotonergic cell line

Many flavonoids, a major group of phenolic plant-derived secondary metabolites, are known to possess estrogen-like bioactivities. However, little is known about their estrogenic properties in the central nervous system due to the lack of suitable cellular models expressing sufficient amounts of functional estrogen receptor β (ERβ). To overcome this deficit, we have created a cellular model, which is serotonergic in origin, to study properties of estrogenic substances by stably transducing RN46A-B14 cells derived from raphe nuclei region of the rat brain with a lentiviral vector encoding a human ERβ. We clearly showed that the transgenic human ERβ is a spontaneously expressed and a functional receptor. We have further assessed the estrogenicity of three different isoflavones and four different naringenin-type flavanones in this cell line utilizing a luciferase reporter gene assay. Genistein (GEN), Daidzein (DAI), Equol (EQ), Naringenin (NAR) and 8-prenylnaringenin (8-PN) showed strong estrogenic activity in a concentration-dependent manner as compared to 7-(O-prenyl)naringenin-4′-acetate (7-O-PN) which was only slightly estrogenic and 6-(1,1-dimethylallyl)naringenin (6-DMAN) that neither showed estrogenic nor anti-estrogenic activity in our model. All observed effects could be antagonized by the anti-estrogen fulvestrant. Moreover, co-treatment of cells with 17β-estradiol (E2) and either GEN or DAI showed a slight additive effect as compared to EQ. On the other hand, 8-PN in addition to 7-O-PN, but not NAR and 6-DMAN, were able to slightly antagonize the responses triggered by E2. Our newly established cellular model may prove to be a useful tool in explicating basic physiological properties of ERβ in the brain and may help unravel molecular and cellular mechanisms involved in serotonergic mood regulation by estrogen or potential plant-derived secondary metabolites.