Estrogenic Potencies of Phytoestrogens Commonly Found in Soybean (Glycine Max) Assessed by use of MMV-Luc Cell Line Bioassay

Abstract

Purpose: Phytoestrogens (PE) are weakly estrogenic compounds synthesized in plants, especially in climatic adversity. The endocrine disruptive activity of PEs and some of their human metabolites are of concern as they have been associated with positive and more so negative health effects.
 Methodology: The transcriptional activities (TAs) of ten PEs (apigenin, daidzein, daidzin, equol, enterodiol, formononetin, genistein, genistin, glycitein, and matairesinol) were measured as induction of the expressed luciferase activity which is correlates with biological effects. These effects were compared to transcription caused by 17β-estradiol (5 nM) hormone (standards) in vitro. This was done by the use of estrogenic receptors in the MMV-Luc cell line using a reporter gene assay tool. 
 Findings: Standard curves for hormone standards were determined and the EC50 for 17β-estradiol was (4.5 x 10-11M). The order of PEs potency for the ER (ERα and ERβ) in the MMV-Luc cell line, as determined from the EC50s (M) of their dose-response curves were in the following order: equol (4.9 x 10-7M) > formononetin (5.7 x 10-6M) > apigenin(2.4 x 10-6M) > genistein (2.1 x 10-6M ) > daidzein(3.3 x 10-5M). Standard curves for the rest were not achieved in the MMV-Luc cell line at the tested concentrations. The % estrogenic potencies of these compounds varied from 9 x 10-3M for equol to 1.4 x 10-4M for daidzein, relative to 17β-estradiol whose percent potency was arbitrarily assigned a value of 100. This study successfully characterized the TA of ten PEs in MMV-Luc cell lines. By achieving and exceeding a full estrogenic effect in MMV-Luc cells, it was indicative that the phytoestrogen transcriptive activity was most likely through non-receptor mechanisms such as enzymatic pathways.
 Recommendations: Although the potential for endocrine disruption by PE was noted in vitro, this study would recommend further in vivo tests. This is because toxicokinetics involving metabolism and bioavailability affects the potencies of the PEs. Further in vitro assays may be designed to investigate the additive effects of phytoestrogens at physiologically relevant concentrations.