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Phytochemical Glyceollins, Isolated from Soy, Mediate Antihormonal Effects through Estrogen Receptor and ß¹

Tulane-Xavier Center for Bioenvironmental Research (M.E.B., B.M.C.-B., L.I.M., B.N.D., S.L., T.E.W., J.A.M.), Molecular and Cellular Biology Program (M.E.B., B.M.C.-B., B.N.D., T.E.W., J.A.M.), and Department of Pharmacology (M.E.B., S.L., J.A.M.), Tulane University Medical Center; Department of Environmental Health Sciences, Tulane University School of Public Health and Tropical Medicine (T.E.W., J.A.M.), New Orleans, Louisiana 70112; Xavier University School of Pharmacy (T.E.W.), New Orleans, Louisiana 70112; and Southern Regional Research Center, United States Department of Agriculture (S.M.B., C.H.C.-W., T.E.C.), New Orleans, Louisiana 70124

Address all correspondence and requests for reprints to: Dr. John A. McLachlan, Tulane-Xavier Center for Bioenvironmental Research, Tulane University Medical Center, 1430 Tulane Avenue, SL-3, New Orleans, Louisiana 70112. E-mail: jmclach{at}mailhost.tcs.tulane.edu

The flavonoid family of phytochemicals, particularly those derived from soy, has received attention regarding their estrogenic activity as well as their effects on human health and disease. In addition to these flavonoids other phytochemicals, including phytostilbene, enterolactone, and lignans, possess endocrine activity. The types and amounts of these compounds in soy and other plants are controlled by both constitutive expression and stress-induced biosynthesis. The health benefits of soy-based foods may, therefore, be dependent upon the amounts of the various hormonally active phytochemicals within these foods. The aim was to identify unique soy phytochemicals that had not been previously assessed for estrogenic or antiestrogenic activity. Here we describe increased biosynthesis of the isoflavonoid phytoalexin compounds, glyceollins, in soy plants grown under stressed conditions. In contrast to the observed estrogenic effects of coumestrol, daidzein, and genistein, we observed a marked antiestrogenic effect of glyceollins on ER signaling, which correlated with a comparable suppression of 17ß-estradiol-induced proliferation in MCF-7 cells. Further evaluation revealed greater antagonism toward ER than ERß in transiently transfected HEK 293 cells. Competition binding assays revealed a greater affinity of glyceollins for ER vs. ERß, which correlated to greater suppression of ER signaling with higher concentrations of glyceollins. In conclusion, we describe the phytoalexin compounds known as glyceollins, which exhibit unique antagonistic effects on ER in both HEK 293 and MCF-7 cells. The glyceollins as well as other phytoalexin compounds may represent an important component of the health effects of soy-based foods.

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