Evaluation of Estrogen Receptor Agonistic Activity of Medicinal Herbs Using Organization for Economic Cooperation and Development Transactivation Assay with Rat Liver S9 Fraction

A number of studies employing different in vitro assays have demonstrated the estrogen-like activity of natural substances. All assays have their advantages and limitations as a screening tool. No single in vitro assay is considered ideal for predicting estrogenic action in a complex in vivo system. To assess agonistic activities of several medicinal herbs on the estrogen receptor (ER) and their metabolic alteration, the Organization for Economic Cooperation and Development (OECD) Performance-Based Test Guideline No. 455 in vitro assay was performed in this study using recombinant VM7Luc4E2 cells in combination with rat liver S9 fractions. Ethanol extracts of medicinal herbs showed binding affinities for ER-alpha and ER-beta at different levels. However, luciferase reporter assay using VM7Luc4E2 cells revealed that only two test extracts [Pueraria lobata root extract (PLE); Glycyrrhiza glabra root extract (GGE)] exhibited ER transcriptional activity when their activities were compared with the response by 17 beta-estradiol. Importantly, incubation of PLE or GGE with rat liver S9 fractions increased their ER transcriptional activities, in particular when phase I metabolic enzymes were activated. Puerarin and glabridin were the most abundant isoflavones found in PLE and GGE, respectively. The present results demonstrate that PLE and GGE possess potential as ER agonists with their metabolic activation. This study also suggests that the application of OECD in vitro assay with rat liver S9 fraction is an efficient screening tool to evaluate estrogenic activities of natural substances.