glabrene and glabridin

The roots of licorice (Glycyrrhiza glabra) are a rich source of flavonoids, in particular, prenylated flavonoids, such as the isoflavan glabridin and the isoflavene glabrene. Fractionation of an ethyl acetate extract from licorice root by centrifugal partitioning chromatography yielded 51 fractions, which were characterized by liquid chromatography-mass spectrometry and screened for activity in yeast estrogen bioassays. One third of the fractions displayed estrogenic activity towards either one or both estrogen receptors (ERs; ERα and ERβ). Glabrene-rich fractions displayed an estrogenic response, predominantly to the ERα. Surprisingly, glabridin did not exert agonistic activity to both ER subtypes. Several fractions displayed higher responses than the maximum response obtained with the reference compound, the natural hormone 17β-estradiol (E(2)). The estrogenic activities of all fractions, including this so-called superinduction, were clearly ER-mediated, as the estrogenic response was inhibited by 20-60% by known ER antagonists, and no activity was found in yeast cells that did not express the ERα or ERβ subtype. Prolonged exposure of the yeast to the estrogenic fractions that showed superinduction did, contrary to E(2), not result in a decrease of the fluorescent response. Therefore, the superinduction was most likely the result of stabilization of the ER, yeast-enhanced green fluorescent protein, or a combination of both. Most fractions displaying superinduction were rich in flavonoids with single prenylation. Glabridin displayed ERα-selective antagonism, similar to the ERα-selective antagonist RU 58668. Whereas glabridin was able to reduce the estrogenic response of E(2) by approximately 80% at 6 × 10(-6) M, glabrene-rich fractions only exhibited agonistic responses, preferentially on ERα.

Topics: Glycyrrhiza; Humans; Isoflavones; Phenols; Plant Extracts; Plant Roots; Receptors, Estrogen; Spectrometry, Mass, Electrospray Ionization

Post-menopausal women have higher incidence of heart diseases compared to pre-menopausal women, suggesting a protective role for estrogen. The recently Women's Health Initiative (WHI) randomized controlled trial concluded that the overall heart risk exceeded benefits from use of combined estrogen and progestin as hormone replacement therapy for an average of five years among healthy postmenopausal US women. Therefore, there is an urgent need for new agents with tissue-selective activity with no deleterious effects. In the present study, we tested the effects on vascular tissues in vitro and in vivo of two natural compounds derived from licorice root: glabridin, the major isoflavan, and glabrene, an isoflavene, both demonstrated estrogen-like activities. Similar to estradiol-17beta (E2), glabridin (gla) stimulated DNA synthesis in human endothelial cells (ECV-304; E304) and had a bi-phasic effect on proliferation of human vascular smooth muscle cells (VSMC). Raloxifene inhibited gla as well as E2 activities. In animal studies, both intact females or after ovariectomy, gla similar to E2 stimulated the specific activity of creatine kinase (CK) in aorta (Ao) and in left ventricle of the heart (Lv). Glabrene (glb), on the other hand, had only the stimulatory effect on DNA synthesis in vascular cells, with no inhibition by raloxifene, suggesting a different mechanism of action. To further elucidate the mechanism of action of glb, cells were pre-incubated with glb and then exposed to either E2 or to gla; the DNA stimulation at low doses was unchanged but there was abolishment of the inhibition of VSMC cell proliferation at high doses as well as inhibition of CK stimulation by both E2 and by gla. We conclude that glb behaved differently than E2 or gla, but similarly to raloxifene, being a partial agonist/antagonist of E2. Glabridin, on the other hand, demonstrated only estrogenic activity. Therefore, we suggest the use of glb with or without E2 as a new agent for modulation of vascular injury and atherogenesis for the prevention of cardiovascular diseases in post-menopausal women.

Topics: Animals; Calcitriol; Cells, Cultured; Creatine Kinase; DNA Replication; Endothelium, Vascular; Estrogens; Female; Glycyrrhiza; In Vitro Techniques; Isoflavones; Male; Ovariectomy; Phenols; Plant Roots; Raloxifene Hydrochloride; Rats; Rats, Wistar; Selective Estrogen Receptor Modulators

Data from both in vivo and in vitro experiments demonstrated that glabridin and glabrene are similar to estradiol-17beta in their stimulation of the specific activity of creatine kinase, although at higher concentrations, but differ in their extent of action and interaction with other drugs. In pre-menopausal human bone cells, the response to estradiol-17beta and glabridin (at higher concentration) was higher than in post-menopausal cells; whereas, glabrene (at higher concentration) was more effective in post-menopausal cells. At both ages, the response to estradiol-17beta and glabridin was enhanced by pretreatment with the less-calcemic Vitamin D analog CB 1093 (CB) and the demonstrably non-calcemic analog JK 1624 F(2)-2 (JKF). The response to glabrene was reduced by this pretreatment. Both glabridin and glabrene stimulated creatine kinase specific activity in diaphyseal bone and epiphyseal cartilage of prepubertal female rats. Daily feeding (3-14 days) of prepubertal female rats with glabridin, estradiol-17beta or their combination, also stimulated creatine kinase specific activity. Glabridine, similarly to estradiol-17beta, also stimulated creatine kinase specific activity in ovariectomized female rats. Raloxifene, in combination with glabridin or estradiol-17beta, demonstrated the phenomenon of mutual annihilation of stimulation of creatine kinase specific activity in both epiphysis and diaphysis. Glabrene activity was not inhibited by raloxifene. Therefore, glabridin shows greater similarity to estradiol-17beta and thus greater potential, with or without Vitamin D, to modulate bone disorders in post-menopausal women.

Topics: Animals; Calcitriol; Creatine Kinase; Drug Combinations; Estrogens; Female; Glycyrrhiza; Growth Plate; Humans; Isoflavones; Osteoblasts; Ovariectomy; Phenols; Plant Roots; Postmenopause; Premenopause; Raloxifene Hydrochloride; Rats; Rats, Wistar; Vitamin D

Ovarian steroid hormones, estrogen and progestin, affect the function of the serotonin neural system by inhibiting serotonin re-uptake through allosteric interaction with the serotonin transporter (SERT) in a nongenomic mechanism. Blocking or reducing serotonin re-uptake at the synapse alleviates depression. The aim of this study was to test the effect of compounds of the isoflavan and isoflavene groups, subclasses of the flavonoids family, on serotonin re-uptake and to compare the results with the effect of other known phytoestrogens like genistein and daidzein to relate the activity of these compounds to their structure. The effect of these compounds on the re-uptake of radioactive serotonin was assayed in HEK-293 cells stably expressed the recombinant human serotonin transporter (hSERT). The results demonstrated that the isoflavans glabridin and 4'-O-methylglabridin (4'-OMeG) and the isoflavene glabrene inhibited serotonin re-uptake by 60, 53 and 47%, respectively, at 50 microM, whereas resorcinol, the isoflavan 2'-O-methylglabridin (2'-OMeG), and the isoflavones genistein and daidzein were inactive. The inhibition of serotonin re-uptake is dose dependant with glabridin and estradiol. These results emphasize the importance of the lipophilic part of the isoflavans, as well as the hydroxyl at position 2' on ring B. In conclusion, this study showed that several isoflavans are unique phytoestrogens, which like estradiol, affects the serotonergic system and inhibits serotonin re-uptake and, thus, potentially may be beneficial for mild to moderate depression in pre- and postmenopausal women.

Topics: Carrier Proteins; Cells, Cultured; Depressive Disorder; Dose-Response Relationship, Drug; Estradiol; Estrogens, Non-Steroidal; Female; Flavonoids; Genistein; Glycyrrhiza; Humans; Isoflavones; Membrane Glycoproteins; Membrane Transport Proteins; Menopause; Molecular Structure; Nerve Tissue Proteins; Phenols; Phytoestrogens; Plant Extracts; Plant Preparations; Resorcinols; Selective Serotonin Reuptake Inhibitors; Serotonin; Serotonin Plasma Membrane Transport Proteins

Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasama, age spots, and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation. The inadequacy of current therapies to treat these conditions as well as high cytotoxicity and mutagenicity, poor skin penetration, and low stability of formulations led us to seek new whitening agents to meet the medical requirements for depigmenting agents. The inhibitory effect of licorice extract on tyrosinase activity was higher than that expected from the level of glabridin in the extract. This led us to test for other components that may contribute to this strong inhibitory activity. Results indicated that glabrene and isoliquiritigenin (2',4',4-trihydroxychalcone) in the licorice extract can inhibit both mono- and diphenolase tyrosinase activities. The IC(50) values for glabrene and isoliquiritigenin were 3.5 and 8.1 microM, respectively, when tyrosine was used as substrate. The effects of glabrene and isoliquiritigenin on tyrosinase activity were dose-dependent and correlated to their ability to inhibit melanin formation in melanocytes. This is the first study indicating that glabrene and isoliquiritigenin exert varying degrees of inhibition on tyrosinase-dependent melanin biosynthesis, suggesting that isoflavenes and chalcones may serve as candidates for skin-lightening agents.

Topics: Cells, Cultured; Chalcone; Chalcones; Dose-Response Relationship, Drug; Glycyrrhiza; Humans; Isoflavones; Kinetics; Melanins; Melanocytes; Monophenol Monooxygenase; Peptides; Phenols; Plant Extracts; Plant Roots; Structure-Activity Relationship; Tyrosine

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 microM) than glabridin (IC50, 5 microM). 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 microM), and ER-independent antiproliferative activity at concentrations >15 microM. This is the first study to indicate that glabrene, an isoflavene exerted varying degrees of ER agonism in different tissues.

Topics: Animals; Breast Neoplasms; Cell Division; Estradiol; Estrogen Receptor Modulators; Estrogens, Non-Steroidal; Female; Glycyrrhiza; HeLa Cells; Humans; Isoflavones; Organ Specificity; Phenols; Phytoestrogens; Phytotherapy; Plant Preparations; Rats; Rats, Wistar; Receptors, Estrogen; Tamoxifen; Transcription, Genetic; Tumor Cells, Cultured