Breast cancer prevention with liquiritigenin from licorice through the inhibition of aromatase and protein biosynthesis in high-risk women's breast tissue

Breast cancer risk continues to increase post menopause. Anti-estrogen therapies are available to prevent postmenopausal breast cancer in high-risk women. However, their adverse effects have reduced acceptability and overall success in cancer prevention. Natural products such as hops (Humulus lupulus) and three pharmacopeial licorice (Glycyrrhiza) species have demonstrated estrogenic and chemopreventive properties, but little is known regarding their effects on aromatase expression and activity as well as pro-proliferation pathways in human breast tissue. We show that Gycyrrhiza inflata (GI) has the highest aromatase inhibition potency among these plant extracts. Moreover, phytoestrogens such as liquiritigenin which is common in all licorice species have potent aromatase inhibitory activity, which is further supported by computational docking of their structures in the binding pocket of aromatase. In addition, GI extract and liquiritigenin suppress aromatase expression in the breast tissue of high-risk postmenopausal women. Although liquiritigenin has estrogenic effects in vitro, with preferential activity through estrogen receptor (ER)-β, it reduces estradiol-induced uterine growth in vivo. It downregulates RNA translation, protein biosynthesis, and metabolism in high-risk women's breast tissue. Finally, it reduces the rate of MCF-7 cell proliferation, with repeated dosing. Collectively, these data suggest that liquiritigenin has breast cancer prevention potential for high-risk postmenopausal women.

Abstract 5263: Licochalcone A is a candidate for breast cancer prevention through its reprogramming of metabolic and antioxidant pathways

Background: Increased adiposity is a risk factor for postmenopausal breast cancer. It is accompanied by protumorigenic effects: chronic low-grade inflammation and elevated levels of reactive oxygen species. Breast cancer risk reducing drugs with proven efficacy have adverse side effects, significantly minimizing their uptake and impact. Effective alternative strategies with lower toxicity are needed. We have shown that licochalcone A (LicA) suppresses aromatase expression and activity, enhances the activity of detoxifying enzymes, and reduces estrogen genotoxic metabolism in cell lines and animal models. However, no previous data exist on the breast tissue of women at substantial risk of breast cancer. We hypothesize that LicA creates a tumor preventive environment in the breast by modulating antioxidant/anti-inflammatory responses in the breast and adipogenesis leading to decreased proliferation.

Methods: We prepared microstructures from the fresh tissue of contralateral unaffected mastectomy specimens of 6 postmenopausal women with incident unilateral breast cancer. After exposing them to DMSO (control) and LicA (5 µM), we performed total RNA sequencing. Differentially expressed genes were identified, and analyzed by gene ontology and pathway membership. The RNA-seq data was utilized also to conduct metabolism flux analysis. Combined enrichment scores > 4 and FDR < 0.05 was considered significant. The NanoString metabolism panel was employed in 6 additional subjects. We performed live cell imaging to monitor proliferation of pre-malignant DCIS.COM, DCIS.COM/ER+ PR+; and malignant MDA-MB-231 (ER- PR-), MCF-7 (ER+ PR+), MCF-7aro, and BRCA1 defective HCC-1937, and HCC3153 cells.

Results: We observed upregulation of antioxidant genes (up to 8-fold), consistent with upregulation of NRF2 and the thioredoxin system, the major regulators of antioxidant pathways. This was accompanied with the significant downregulation of RELA- and NF-kB1-dependent inflammatory pathways. In addition, we observed decreased expression of the pro-adipogenic transcription factors SREBF1 and SREBF2, which may explain the downregulation (4 to 32-fold) of cholesterol biosynthesis and transport, and lipid metabolism genes. Metabolism studies confirmed these data and demonstrated a robust increase in the pentose phosphate shunt and NAD(P)H generation without enhancing ribose 5 phosphate formation, suggesting an antioxidant and anti-proliferative environment. LicA also suppressed proliferation of pre-malignant and malignant cells, with sustained effects on aggressive cells at doses < 10 µM.

Conclusion: Our data suggest that LicA is a good candidate for breast cancer prevention through modulation of metabolic and antioxidant pathways leading to decreased proliferation. Our ongoing in vivo study will further demonstrate the efficacy of LicA for breast cancer prevention.

Citation Format: Atieh Hajirahimkhan, Elizabeth Bartom, Sriram Chandrasekaran, Xiaoling Xuei, Susan Clare, Seema Khan. Licochalcone A is a candidate for breast cancer prevention through its reprogramming of metabolic and antioxidant pathways. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5263.

Abstract P2-08-01: Licochalcone A from licorice reprograms metabolic and antioxidant pathways in the breast leading to a tumor preventive environment

Background: Increased adiposity is a risk factor for postmenopausal breast cancer. It is often accompanied by chronic low-grade inflammation and elevated levels of reactive oxygen species, which drive breast tumorigenesis. Risk reducing drugs such as selective estrogen receptor modulators and aromatase inhibitors, which have demonstrated efficacy, have had a significantly low acceptance among women at high risk for breast cancer. This hesitancy is mainly due to the adverse side effects of these medications such as vasomotor symptoms, osteoporosis, thromboembolism, and uterine cancer. Therefore, alternative strategies with lower toxicity and greater acceptability are needed. We have previously shown that licochalcone A (LicA) from licorice (Glycyrrhiza inflata), which has osteogenic effects, suppresses aromatase expression and activity, enhances the activity of detoxifying enzymes, and reduces estrogen genotoxic metabolism in cell lines and animal models. However, its effects on the breast tissue of high-risk women are understudied. We hypothesize that LicA creates a tumor preventive environment in the breast by locally modulating adipogenesis and antioxidant/anti-inflammatory responses leading to decreased proliferation. Methods: We prepared microstructures from fresh tissue of contralateral unaffected mastectomy specimens of 6 postmenopausal women with incident unilateral breast cancer. We exposed these to DMSO (control) and LicA (5 µM) for 24 h. Employing total RNA sequencing, we examined differential gene expression between treated and control samples. Up-regulated and down-regulated genes were analyzed using Enrichr gene ontology (GO) pathway analysis. Enriched pathways with combined enrichment scores > 4 and FDR < 0.05 were considered statistically significant. Metabolism flux analysis was performed (FDR < 0.05). Live cell imaging to monitor proliferation of pre-malignant DCIS.COM, DCIS.COM/ER+ PR+; and malignant MDA-MB-231 (ER- PR-), MCF-7 (ER+ PR+), MCF-7aro, and BRCA1 defective HCC-1937, and HCC3153 cells was conducted using IncuCyte. Single versus repeated dosing of various concentrations of LicA were also evaluated. Results: We observed significant (P < 0.05) upregulation up to 8-fold of antioxidant genes, consistent with significant upregulation of NRF2, the major regulator of antioxidant pathways. This was accompanied by significant (P < 0.05) downregulation of NF-kB dependent inflammatory pathways. In addition, we observed the significant (P < 0.05) downregulation, ranging from 4 to 32-fold of cholesterol biosynthesis and transport, steroid hormone biosynthesis, as well as lipid metabolism genes, consistent with the profound downregulation of SREBF1 and SREBF2, which encode the master regulator of adipogenesis, SREBP. Metabolic flux results demonstrated a robust increase (FDR < 0.05) in the pentose phosphate shunt and NAD(P)H generation without enhancing ribose 5 phosphate formation, confirming an antioxidant and anti-proliferative environment. Likewise, LicA suppressed proliferation of pre-malignant and malignant cells dose- and time-dependently. Repeated dosing of lower concentrations of LicA (< 10 µM) demonstrated sustained antiproliferative effects even in the aggressive cancer cell lines. Conclusion: Our data suggest that LicA can generate a tumor-preventive breast microenvironment by reprogramming metabolic pathways involved in steroid and lipid homeostasis and antioxidant responses. These observations along with its low toxicity, suggest that LicA is a good candidate for further investigation as a breast cancer prevention agent.

Citation Format: Atieh Hajirahimkhan, Elizabeth T. Bartom, Sriram Chandrasekaran, Susan Clare, Seema Khan. Licochalcone A from licorice reprograms metabolic and antioxidant pathways in the breast leading to a tumor preventive environment. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-08-01.

Abstract P1-11-01: Modulation of the high risk postmenopausal breast tissue genomic profiles with licorice and its bioactive compounds

Introduction: Breast cancer risk continues to rise following menopause, despite the cessation of ovarian estrogen synthesis. High risk women are often hesitant to take anti-endocrine therapies for breast cancer prevention. Therefore, alternative strategies with greater acceptability are needed. Popular botanicals for menopausal health such as licorice (Glycyrrhiza inflata, GI) and its bioactive compounds liquiritigenin (LigF, phytoestrogen) and licochalcone A (LicA, chalcone) have been studied for their targeted estrogenic and chemopreventive properties in vitro and in vivo. However, their effects on the breast tissue of high risk women are understudied. We hypothesize that these agents create a tumor preventive environment in the breast by locally modulating metabolism, steroid hormone biosynthesis, inflammation, antioxidant response, and proliferation. Methods: We prepared organoids from fresh surgically removed contralateral unaffected breast tissue of 6 high-risk postmenopausal women undergoing bilateral mastectomy due to incident unilateral breast cancer. We exposed these organoids to DMSO (control), GI (5 µg/mL), LigF (5 µM), and LicA (5 µM) for 24 h. After total RNA sequencing, we performed differential gene expression between treatments and controls using the limma R package. Enrichment results were generated by analyzing the up-regulated and down-regulated gene sets using Enrichr. A gene ontology (GO) pathway analysis was performed. The enriched pathways with combined enrichment scores > 4 and FDR < 0.05 were considered statistically significant. Results: Among the top ranked biological pathways we observed significant upregulation of Nrf2 and phase II metabolism pathways, and the downregulation of steroid biosynthesis, metabolic processes such as estrogen metabolism, citrate cycle, serine and one carbon metabolism, as well as the cell cycle and DNA replication in GI treated samples. For LigF treated group, significant downregulation of inflammatory response, cell cycle, and the integrated breast cancer pathways were among the top ranked processes. For LicA treated samples, pathways associated with glutathione metabolism, Nrf2, response to oxidative stress, and unfolded protein response were significantly upregulated while steroid hormone biosynthesis, lipid metabolism, fatty acid biosynthesis, and glucose metabolism were among the top ranked downregulated pathways.Conclusions: Our data suggests that GI and its components LigF and LicA can modulate breast microenvironment by reducing inflammation, steroid hormone biosynthesis, cellular metabolism, and proliferation. They can also enhance protection against oxidative and cellular stress. These observations along with the popularity of natural products, suggests that licorice GI and its bioactive compounds might have the potential to create a tumor preventive breast microenvironment in high risk postmenopausal women, and need to be further studied.

Citation Format: Atieh Hajirahimkhan, Shao-Nong Chen, Guido F Pauli, Elizabeth Bartom, Susan Clare, Seema A Khan. Modulation of the high risk postmenopausal breast tissue genomic profiles with licorice and its bioactive compounds [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-11-01.

Abstract 2566: The potential role of licorice and its bioactive compounds in promoting a tumor preventive environment in the postmenopausal breast

Introduction: our purpose was to define if licorice and its main bioactive compounds can suppress aromatase expression/activity and Nrf2 dependent detoxification pathways in the postmenopausal breast. This chemopreventive potential has not previously been reported in preclinical models of high-risk postmenopausal breast.

Methods: Inhibition of aromatase activity by three licorice extracts (Glycyrrhiza species), and their bioactive compounds, (liquiritigenin; LigF, isoliquiritigenin; LigC, 8-prenylapigenin; 8-PA, and licochalcone A; LicA) were evaluated fluorometrically, using aromatase supersomes. Computational docking was performed to assess the binding of the bioactive compounds to the binding pocket of aromatase crystal structure compared to the known aromatase inhibitors, letrozole (non-steroidal) and exemestane (steroidal). Using qPCR, the effects of treatments on the expression of aromatase (CYP19A1) mRNA and Nrf2 dependent detoxification enzyme NADPH:quinone oxidoreductase 1 (NQO1) in breast microstructures obtained from high risk postmenopausal women were evaluated.

Results: Among the three medicinally used licorice species, Glycyrrhiza inflata (GI) showed the highest aromatase inhibitory potency (IC50 ≈ 1 µg/mL). Licorice phytoestrogens, LigF (400 nM or 0.1 µg/mL), and 8-PA (IC50 ≈ 590 nM or 0.2 µg/mL) exhibited the highest potency compared to the other tested licorice compounds. Computational docking suggested that these phytoestrogens bind to the aromatase binding pocket like the aromatase inhibitor, letrozole. This effect was not observed with non-estrogenic bioactive compounds of licorice, LigC and LicA (specific to GI). In breast microstructures obtained from high risk postmenopausal women, expression of aromatase mRNA was suppressed by GI (30%, P < 0.05), LigF (20%, P < 0.05), and LicA (45%, P < 0.05), while the expression of NQO1 mRNA was enhanced by LicA (200%, P < 0.0001).

Conclusions: Licorice species, and their bioactive compounds inhibited aromatase activity in vitro. In the breast microstructures, GI, its compounds LigF and LicA suppressed aromatase expression, and LicA enhanced NQO1 induction, significantly. Further studies will further elucidate the potential of these natural products for promoting a breast tumor preventive environment in postmenopausal women.

Citation Format: Atieh Hajirahimkhan, Caitlin Howell, Shao-Nong Chen, Susan E. Clare, Guido F. Pauli, Judy L. Bolton, Birgit M. Dietz, Seema A. Khan. The potential role of licorice and its bioactive compounds in promoting a tumor preventive environment in the postmenopausal breast [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2566.

Abstract PS8-10: Inhibition of estrogen biosynthesis by hops, licorice species, and their bioactive compounds

Introduction: Breast cancer risk continues to rise following menopause, despite the cessation of ovarian estrogen synthesis. Pathways involving increased aromatase activity and inflammation in the breast microenvironment are implicated. Their concerted disruption could be protective against breast cancer. Popular botanicals for menopausal health, such as hops (Humulus lupulus), three licorice species (Glycyrrhiza glabra, Glycyrrhiza inflata, Glycyrrhiza uralensis) extracts, and their bioactive compounds have shown estrogenic and chemopreventive properties in vitro and in vivo. Their effects on aromatase expression and activity, and on inflammatory responses in the breast are not well characterized.Methods: Inhibition of aromatase activity by hops extract, its compounds (8-prenylnaringenin, 6-prenylnaringenin, and xanthohumol); three licorice extracts, and their bioactive compounds, (liquiritigenin, isoliquiritigenin, 8-prenylapigenin, and licochalcone A) were evaluated fluorometrically, using aromatase supersomes. Computational docking was performed to assess the binding of the bioactive compounds to the binding pocket of aromatase crystal structure compared to the known aromatase inhibitors, letrozole (non-steroidal) and exemestane (steroidal). Using qPCR, the effect of treatments on aromatase mRNA expression in breast microstructures of menopausal women was evaluated. The effects of hops and licorice on transactivation of NF-kB in MCF-7 breast cancer cells were studied, using a luciferase assay.Results: Among the extracts, one of the licorice species, Glycyrrhiza inflata showed the highest aromatase inhibitory potency (IC50 ≈ 1 µg/mL). Among the compounds, the phytoestrogens 8-prenylnaringenin (IC50 = 50 nM or 17 ng/mL) from hops, liquiritigenin (400 nM or 0.1 µg/mL), and 8-prenylapigenin (IC50 ≈ 590 nM or 0.2 µg/mL) from licorice exhibited the highest potency. Computational docking suggested that these phytoestrogens bind to the aromatase binding pocket like the aromatase inhibitor, letrozole. This effect was not observed with non-estrogenic bioactive compounds including 6-prenylnaringenin and xanthohumol from hops as well as isoliquiritigenin and licochalcone A from licorice. Hops and 8-prenylnaringenin reduced aromatase expression in breast microstructures by 60% (P < 0.05). Moreover, hops and licorice extracts suppressed NF-kB-luciferase activity by 70% in MCF-7 cells (P< 0.01). Conclusions: Hops, licorice species, and their phytoestrogens inhibit aromatase activity and expression. The extracts suppress NF-kB transactivation in MCF-7 cells, suggesting inhibition of inflammatory response. Further studies will better elucidate the potential of these popular botanicals and their bioactive compounds for preventing breast cancer in menopausal women.

Citation Format: Atieh Hajirahimkhan, Caitlin Howell, Tareisha Dunlap, Shao-Nong Chen, Susan E. Clare, Guido F. Pauli, Judy L. Bolton, Birgit M. Dietz, Seema A. Khan. Inhibition of estrogen biosynthesis by hops, licorice species, and their bioactive compounds [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-10.

SAR Study on Estrogen Receptor α/β Activity of (Iso)flavonoids: Importance of Prenylation, C-Ring (Un)Saturation, and Hydroxyl Substituents

Many botanicals used for women's health contain estrogenic (iso)flavonoids. The literature suggests that estrogen receptor beta (ERβ) activity can counterbalance estrogen receptor alpha (ERα)-mediated proliferation, thus providing a better safety profile. A structure-activity relationship study of (iso)flavonoids was conducted to identify ERβ-preferential structures, overall estrogenic activity, and ER subtype estrogenic activity of botanicals containing these (iso)flavonoids. Results showed that flavonoids with prenylation on C8 position increased estrogenic activity. C8-prenylated flavonoids with C2-C3 unsaturation resulted in increased ERβ potency and selectivity [e.g., 8-prenylapigenin (8-PA), EC₅₀ (ERβ): 0.0035 ± 0.00040 μM], whereas 4'-methoxy or C3 hydroxy groups reduced activity [e.g., icaritin, EC₅₀ (ERβ): 1.7 ± 0.70 μM]. However, nonprenylated and C2-C3 unsaturated isoflavonoids showed increased ERβ estrogenic activity [e.g., genistein, EC₅₀ (ERβ): 0.0022 ± 0.0004 μM]. Licorice (Glycyrrhiza inflata, [EC₅₀ (ERα): 1.1 ± 0.20; (ERβ): 0.60 ± 0.20 μg/mL], containing 8-PA, and red clover [EC₅₀ (ERα): 1.8 ± 0.20; (ERβ): 0.45 ± 0.10 μg/mL], with genistein, showed ERβ-preferential activity as opposed to hops [EC₅₀ (ERα): 0.030 ± 0.010; (ERβ): 0.50 ± 0.050 μg/mL] and Epimedium sagittatum [EC₅₀ (ERα): 3.2 ± 0.20; (ERβ): 2.5 ± 0.090 μg/mL], containing 8-prenylnaringenin and icaritin, respectively. Botanicals with ERβ-preferential flavonoids could plausibly contribute to ERβ-protective benefits in menopausal women.

The Multiple Biological Targets of Hops and Bioactive Compounds

Botanical dietary supplements for women's health are increasingly popular. Older women tend to take botanical supplements such as hops as natural alternatives to traditional hormone therapy to relieve menopausal symptoms. Especially extracts from spent hops, the plant material remaining after beer brewing, are enriched in bioactive prenylated flavonoids that correlate with the health benefits of the plant. The chalcone xanthohumol (XH) is the major prenylated flavonoid in spent hops. Other less abundant but important bioactive prenylated flavonoids are isoxanthohumol (IX), 8-prenylnaringenin (8-PN), and 6-prenylnaringenin (6-PN). Pharmacokinetic studies revealed that these flavonoids are conjugated rapidly with glucuronic acid. XH also undergoes phase I metabolism in vivo to form IX, 8-PN, and 6-PN. Several hop constituents are responsible for distinct effects linked to multiple biological targets, including hormonal, metabolic, inflammatory, and epigenetic pathways. 8-PN is one of the most potent phytoestrogens and is responsible for hops' estrogenic activities. Hops also inhibit aromatase activity, which is linked to 8-PN. The weak electrophile, XH, can activate the Keap1-Nrf2 pathway and turn on the synthesis of detoxification enzymes such as NAD(P)H-quinone oxidoreductase 1 and glutathione S-transferase. XH also alkylates IKK and NF-κB, resulting in anti-inflammatory activity. Antiobesity activities have been described for XH and XH-rich hop extracts likely through activation of AMP-activated protein kinase signaling pathways. Hop extracts modulate the estrogen chemical carcinogenesis pathway by enhancing P450 1A1 detoxification. The mechanism appears to involve activation of the aryl hydrocarbon receptor (AhR) by the AhR agonist, 6-PN, leading to degradation of the estrogen receptor. Finally, prenylated phenols from hops are known inhibitors of P450 1A1/2; P450 1B1; and P450 2C8, 2C9, and 2C19. Understanding the biological targets of hop dietary supplements and their phytoconstituents will ultimately lead to standardized botanical products with higher efficacy, safety, and chemopreventive properties.

Estrogen Receptor (ER) Subtype Selectivity Identifies 8-Prenylapigenin as an ERβ Agonist from Glycyrrhiza inflata and Highlights the Importance of Chemical and Biological Authentication

Postmenopausal women are increasingly using botanicals for menopausal symptom relief due to the increased breast cancer risk associated with traditional estrogen therapy. The deleterious effects of estrogens are associated with estrogen receptor (ER)α-dependent proliferation, while ERβ activation could enhance safety by opposing ERα effects. Three medicinal licorice species, Glycyrrhiza glabra ( G. glabra), G. uralensis, and G. inflata, were studied for their differential estrogenic efficacy. The data showed higher estrogenic potency for G. inflata in an alkaline phosphatase induction assay in Ishikawa cells (ERα) and an estrogen responsive element (ERE)-luciferase assay in MDA-MB-231/β41 breast cancer cells (ERβ). Bioassay-guided fractionation of G. inflata led to the isolation of 8-prenylapigenin (3). Surprisingly, a commercial batch of 3 was devoid of estrogenic activity. Quality control by MS and qNMR revealed an incorrect compound, 4'- O-methylbroussochalcone B (10), illustrating the importance of both structural and purity verification prior to any biological investigations. Authentic and pure 3 displayed 14-fold preferential ERβ agonist activity. Quantitative analyses revealed that 3 was 33 times more concentrated in G. inflata compared to the other medicinal licorice extracts. These data suggest that standardization of G. inflata to 3 might enhance the safety and efficacy of G. inflata supplements used for postmenopausal women's health.

Botanicals and Their Bioactive Phytochemicals for Women's Health

Botanical dietary supplements are increasingly popular for women's health, particularly for older women. The specific botanicals women take vary as a function of age. Younger women will use botanicals for urinary tract infections, especially Vaccinium macrocarpon (cranberry), where there is evidence for efficacy. Botanical dietary supplements for premenstrual syndrome (PMS) are less commonly used, and rigorous clinical trials have not been done. Some examples include Vitex agnus-castus (chasteberry), Angelica sinensis (dong quai), Viburnum opulus/prunifolium (cramp bark and black haw), and Zingiber officinale (ginger). Pregnant women have also used ginger for relief from nausea. Natural galactagogues for lactating women include Trigonella foenum-graecum (fenugreek) and Silybum marianum (milk thistle); however, rigorous safety and efficacy studies are lacking. Older women suffering menopausal symptoms are increasingly likely to use botanicals, especially since the Women's Health Initiative showed an increased risk for breast cancer associated with traditional hormone therapy. Serotonergic mechanisms similar to antidepressants have been proposed for Actaea/Cimicifuga racemosa (black cohosh) and Valeriana officinalis (valerian). Plant extracts with estrogenic activities for menopausal symptom relief include Glycine max (soy), Trifolium pratense (red clover), Pueraria lobata (kudzu), Humulus lupulus (hops), Glycyrrhiza species (licorice), Rheum rhaponticum (rhubarb), Vitex agnus-castus (chasteberry), Linum usitatissimum (flaxseed), Epimedium species (herba Epimedii, horny goat weed), and Medicago sativa (alfalfa). Some of the estrogenic botanicals have also been shown to have protective effects against osteoporosis. Several of these botanicals could have additional breast cancer preventive effects linked to hormonal, chemical, inflammatory, and/or epigenetic pathways. Finally, although botanicals are perceived as natural safe remedies, it is important for women and their healthcare providers to realize that they have not been rigorously tested for potential toxic effects and/or drug/botanical interactions. Understanding the mechanism of action of these supplements used for women's health will ultimately lead to standardized botanical products with higher efficacy, safety, and chemopreventive properties.

Induction of NAD(P)H:Quinone Oxidoreductase 1 (NQO1) by Glycyrrhiza Species Used for Women's Health: Differential Effects of the Michael Acceptors Isoliquiritigenin and Licochalcone A

For the alleviation of menopausal symptoms, women frequently turn to botanical dietary supplements, such as licorice and hops. In addition to estrogenic properties, these botanicals could also have chemopreventive effects. We have previously shown that hops and its Michael acceptor xanthohumol (XH) induced the chemoprevention enzyme,

NAD(P)H

quinone oxidoreductase 1 (NQO1), in vitro and in vivo. Licorice species could also induce NQO1, as they contain the Michael acceptors isoliquiritigenin (LigC) found in Glycyrrhiza glabra (GG), G. uralensis (GU), G. inflata (GI), and licochalcone A (LicA) which is only found in GI. These licorice species and hops induced NQO1 activity in murine hepatoma (Hepa1c1c7) cells; hops ≫ GI > GG ≅ GU. Similar to the known chemopreventive compounds curcumin (turmeric), sulforaphane (broccoli), and XH, LigC and LicA were active dose-dependently; sulforaphane ≫ XH > LigC > LicA ≅ curcumin ≫ liquiritigenin (LigF). Induction of the antioxidant response element luciferase in human hepatoma (HepG2-ARE-C8) cells suggested involvement of the Keap1-Nrf2 pathway. GG, GU, and LigC also induced NQO1 in nontumorigenic breast epithelial MCF-10A cells. In female Sprague-Dawley rats treated with GG and GU, LigC and LigF were detected in the liver and mammary gland. GG weakly enhanced NQO1 activity in the mammary tissue but not in the liver. Treatment with LigC alone did not induce NQO1 in vivo most likely due to its conversion to LigF, extensive metabolism, and its low bioavailability in vivo. These data show the chemopreventive potential of licorice species in vitro could be due to LigC and LicA and emphasize the importance of chemical and biological standardization of botanicals used as dietary supplements. Although the in vivo effects in the rat model after four-day treatment are minimal, it must be emphasized that menopausal women take these supplements for extended periods of time and long-term beneficial effects are quite possible.

Biological and chemical standardization of a hop (Humulus lupulus) botanical dietary supplement

Concerned about the safety of conventional estrogen replacement therapy, women are using botanical dietary supplements as alternatives for the management of menopausal symptoms such as hot flashes. Before botanical dietary supplements can be evaluated clinically for safety and efficacy, botanically authenticated and standardized forms are required. To address the demand for a standardized, estrogenic botanical dietary supplement, an extract of hops (Humulus lupulus L.) was developed. Although valued in the brewing of beer, hop extracts are used as anxiolytics and hypnotics and have well-established estrogenic constituents. Starting with a hop cultivar used in the brewing industry, spent hops (the residue remaining after extraction of bitter acids) were formulated into a botanical dietary supplement that was then chemically and biologically standardized. Biological standardization utilized the estrogen-dependent induction of alkaline phosphatase in the Ishikawa cell line. Chemical standardization was based on the prenylated phenols in hops that included estrogenic 8-prenylnaringenin, its isomer 6-prenylnaringenin, and pro-estrogenic isoxanthohumol and its isomeric chalcone xanthohumol, all of which were measured using high-performance liquid chromatography-tandem mass spectrometry. The product of this process was a reproducible botanical extract suitable for subsequent investigations of safety and efficacy.

Evaluation of estrogenic activity of licorice species in comparison with hops used in botanicals for menopausal symptoms

The increased cancer risk associated with hormone therapies has encouraged many women to seek non-hormonal alternatives including botanical supplements such as hops (Humulus lupulus) and licorice (Glycyrrhiza spec.) to manage menopausal symptoms. Previous studies have shown estrogenic properties for hops, likely due to the presence of 8-prenylnarigenin, and chemopreventive effects mainly attributed to xanthohumol. Similarly, a combination of estrogenic and chemopreventive properties has been reported for various Glycyrrhiza species. The major goal of the current study was to evaluate the potential estrogenic effects of three licorice species (Glycyrrhiza glabra, G. uralensis, and G. inflata) in comparison with hops. Extracts of Glycyrrhiza species and spent hops induced estrogen responsive alkaline phosphatase activity in endometrial cancer cells, estrogen responsive element (ERE)-luciferase in MCF-7 cells, and Tff1 mRNA in T47D cells. The estrogenic activity decreased in the order H. lupulus > G. uralensis > G. inflata > G. glabra. Liquiritigenin was found to be the principle phytoestrogen of the licorice extracts; however, it exhibited lower estrogenic effects compared to 8-prenylnaringenin in functional assays. Isoliquiritigenin, the precursor chalcone of liquiritigenin, demonstrated significant estrogenic activities while xanthohumol, a metabolic precursor of 8-prenylnaringenin, was not estrogenic. Liquiritigenin showed ERβ selectivity in competitive binding assay and isoliquiritigenin was equipotent for ER subtypes. The estrogenic activity of isoliquiritigenin could be the result of its cyclization to liquiritigenin under physiological conditions. 8-Prenylnaringenin had nanomolar estrogenic potency without ER selectivity while xanthohumol did not bind ERs. These data demonstrated that Glycyrrhiza species with different contents of liquiritigenin have various levels of estrogenic activities, suggesting the importance of precise labeling of botanical supplements. Although hops shows strong estrogenic properties via ERα, licorice might have different estrogenic activities due to its ERβ selectivity, partial estrogen agonist activity, and non-enzymatic conversion of isoliquiritigenin to liquiritigenin.

Botanical modulation of menopausal symptoms: mechanisms of action?

Menopausal women suffer from a variety of symptoms, including hot flashes and night sweats, which can affect quality of life. Although it has been the treatment of choice for relieving these symptoms, hormone therapy has been associated with increased breast cancer risk leading many women to search for natural, efficacious, and safe alternatives such as botanical supplements. Data from clinical trials suggesting that botanicals have efficacy for menopausal symptom relief have been controversial, and several mechanisms of action have been proposed including estrogenic, progestogenic, and serotonergic pathways. Plant extracts with potential estrogenic activities include soy, red clover, kudzu, hops, licorice, rhubarb, yam, and chasteberry. Botanicals with reported progestogenic activities are red clover, hops, yam, and chasteberry. Serotonergic mechanisms have also been proposed since women taking antidepressants often report a reduction in hot flashes and night sweats. Black cohosh, kudzu, kava, licorice, and dong quai all either have reported 5-hydroxytryptamine receptor 7 ligands or inhibit serotonin reuptake, therefore have potential serotonergic activities. Understanding the mechanisms of action of these natural remedies used for women's health could lead to more efficacious formulations and to the isolation of active components which have the potential of becoming effective medications in the future.

Dynamic residual complexity of the isoliquiritigenin-liquiritigenin interconversion during bioassay

Bioactive components in food plants can undergo dynamic processes that involve multiple chemical species. For example, 2'-hydroxychalcones can readily isomerize into flavanones. Although chemically well documented, this reaction has barely been explored in the context of cell-based assays. The present time-resolved study fills this gap by investigating the isomerization of isoliquiritigenin (a 2'-hydroxychalcone) and liquiritigenin (a flavanone) in two culture media (Dulbecco's modified eagle medium and Roswell Park Memorial Institute medium) with and without MCF-7 cells, using high-performance liquid chromatography-diode array detector-electrospray ionization/atmospheric pressure chemical ionization-mass spectrometry for analysis. Both compounds were isomerized and epimerized under all investigated biological conditions, leading to mixtures of isoliquiritigenin and R/S-liquiritigenin, with 19.6% R enantiomeric excess. Consequently, all three species can potentially modulate the biological responses. This exemplifies dynamic residual complexity and demonstrates how both nonchiral reactions and enantiomeric discrimination can occur in bioassay media, with or without cells. The findings highlight the importance of controlling in situ chemical reactivity, influenced by biological systems when evaluating the mode of action of bioactives.