Journal of Steroid Biochemistry & Molecular Biology 78 (2001) 291 – 298 Estrogen-like activity of glabrene and other constituents isolated from licorice root Snait Tamir a , Mark Eizenberg a , Dalia Somjen b , Sarit Izrael a , Jacob Vaya a, * a Laboratory of Natural Compounds for Medicinal Use, Migal -Galilee Technological Center, Kiryat Shmona 10200, Israel b Institute of Endocrinology, Sourasky Medical Center and Sackler Faculty of Medicine, Tel -Ai Uniersity, Tel Ai, Israel Received 17 April 2001; accepted 21 May 2001 Abstract Licorice root extract and its major isoflavan, glabridin, exhibited varying degrees of estrogen receptor (ER) agonism in different tissues in vitro and in vivo. Animals fed with licorice extract, compared with estradiol and glabridin, showed an increase in creatine kinase (CK) activity, a known marker for estrogen responsive genes, which was higher than expected from the levels of glabridin in the extract. This led us to test for other components that may contribute to this strong estrogen agonist activity. Results indicated that glabrene and isoliquiritigenin, (2,4,4-three hydroxy chalcone) (ILC) in the licorice extract can bind to the human ER with higher affinity (IC50, 1 and 0.5 M) than glabridin (IC50, 5 M). The stimulatory effects of glabrene in vivo were tissue specific and similar to those of estradiol. The effect of increasing concentrations of glabrene and ILC on the growth of breast tumor cell were biphasic. Both showed an ER-dependent growth-promoting effect at low concentrations (10 nM – 10 M), and ER-independent antiproliferative activity at concentrations 15 M. This is the first study to indicate that glabrene, an isoflavene exerted varying degrees of ER agonism in different tissues. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Licorice root; Glabridin; Estrogen receptor www.elsevier.com/locate/jsbmb 1. Introduction The consumption of Glycyrrhiza glabra, the licorice plant, can be traced for the past 6000 years [1]. The licorice root has long been employed as a flavoring and sweetening agent, as well as a demulcent and expecto- rant in western countries. At present, glycyrrhizin and its aglycone, glycyrrhetinic acid, the main components in licorice root, are clinically used in treatments of hyperlipidemia, atherosclerosis, viral diseases and aller- gic inflammation such as chronic hepatitis and atopic dermatitis [2,3]. Minor components of licorice demon- strated significant antimicrobial activity in vitro [4,5] and antioxidant activity [6,7]. We reported recently that the major isoflavan, glabridin, isolated from licorice root exhibited varying degrees of estrogen receptor (ER) agonism in different estrogen responsive tissues [8]. Glabrene, an isoflavene from licorice root, has two hydroxyl groups at 2 and 7 positions, a 2,2-dimethyl-- pyran ring fused to B ring, and a double bond between carbon 3 and 4 in C ring, which confers maximal conjugation of the double bonds on the molecule (Fig. 1). This conjugation increases the stability of the phe- noxyl radical, which is formed after the donation of an electron, resulting in increased antioxidative activity [6,7]. Hispaglabridin A and hispaglabridin B (Fig. 1), two additional derivatives isolated from licorice root, were also tested for their estrogenic activity. The structures of these two compounds are similar to that of glabridin, except that hispaglabridin A has an isoprenyl side chain attached to the 3 position, which increases the lipophilic characteristics of the isoflavan in comparison to glabridin. Isoprenylchalcone (IPC) and isoliquiritigenin, 2,4,4- three hydroxy chalcone (ILC) are two chalcones iso- lated and identified from licorice extract [6]. The ILC derivative, with the more lipophilic character was found * Corresponding author. Tel.: +972-4-695-3512; fax: +972-4-694- 4980. E-mail address: vaya@migal.org.il (J. Vaya). 0960-0760/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0960-0760(01)00093-0