Soy Isoflavone Genistein Research Articles

Dose-dependent effects of a genistein-enriched diet in the heart of ovariectomized mice

The isoflavone genistein is used as a pharmacological compound and as a food supplement. The duration and the level of exposure of humans to genistein are considerable. However, the magnitude of genistein-supplemented dietary interventions necessary to induce any changes in the heart has not been studied so far. The aim of this study was to investigate the dose-dependent effects of dietary genistein in the disease- and stress-free mouse heart. Female C57BL/6J mice at the age of 2 months were ovariectomized and randomly assigned to feed on diets with seven different genistein doses (0.01, 0.03, 0.1, 0.3, 1, 3 and 10 g genistein/kg food) for 3 months. Mice with intact ovaries or ovariectomized fed on soy-free diets were used as controls. Ovariectomy led to an increase in body weight, while the two highest genistein doses prevented this increase. Absolute uterus weight was decreased in the ovariectomized group and all genistein groups except for the 10 g/kg food group compared with the intact ovaries/soy-free group. Considering cardiac mass, although the 3 and 10 g/kg food groups had significantly lower absolute heart weight than all other groups, heart-to-body-weight ratios did not differ between these two groups and the intact ovaries/soy-free group, while all remaining groups had smaller ratios. Next, we observed dose-dependent effects of genistein on cardiac gene expression. The present findings indicate that exposure of female mice to the soy isoflavone genistein influences body weight and cardiac mass and gene expression in a dose-dependent manner. Human exposure to dietary genistein supplements may influence cardiac function.

Formation of Phosphoglycosides in Caenorhabditis elegans: A Novel Biotransformation Pathway

Background Caenorhabditis elegans (C. elegans) has become a widely used model to explore the effect of food constituents on health as well as on life-span extension. The results imply that besides essential nutrients several flavonoids are able to impact the aging process. What is less investigated is the bioavailability and biotransformation of these compounds in C. elegans. In the present study, we focused on the soy isoflavone genistein and its metabolism in the nematode as a basis for assessing whether this model system mimics the mammalian condition.Principal Findings C. elegans was exposed to 100 µM genistein for 48 hours. The worm homogenate was extracted and analyzed by liquid chromatography (LC). 11 metabolites of genistein were detected and characterized using LC electrospray ionization mass spectrometry. All genistein metabolites formed by C. elegans were found to be sugar conjugates, primarily genistein-O-glucosides. The dominant metabolite was identified as genistein-7-O-phosphoglucoside. Further interesting metabolites include two genistein-di-O-glycosides, a genistein-O-disaccharide as well as a genistein-O-phosphodisaccharide.Conclusions/SignificanceOur study provides evidence for a novel biotransformation pathway in C. elegans leading to conjugative metabolites which are not known for mammals. The metabolism of genistein in mammals and in C. elegans differs widely which may greatly impact the bioactivity. These differences need to be appropriately taken into consideration when C. elegans is used as a model to assess possible health or aging effects.

Inhibition of ABCG2/BCRP transporter by soy isoflavones genistein and daidzein: Effect on plasma and milk levels of danofloxacin in sheep

Danofloxacin is a synthetic fluoroquinolone antibacterial agent and a substrate for ATP-binding cassette transporter G2/breast cancer resistance protein (ABCG2/BCRP). This protein actively extrudes drugs from cells in the intestine, liver, kidney, and other organs, such as the mammary gland. The purpose of this study was to determine whether genistein and daidzein, isoflavones present in soy and known inhibitors of ABCG2, could diminish danofloxacin secretion into milk. The results obtained from BCRP-transduced MDCK-II cells (Mardin-Darby canine kidney) showed that both isoflavones efficiently inhibited the in vitro transport of the drug. In addition, danofloxacin transport into milk was studied in Assaf sheep.The experimental design with ewes (n=18) included ewes fed with standard forage, soy-enriched forage for 15days prior to the experiment or standard forage paired with orally administered exogenous genistein and daidzein. The danofloxacin levels in the milk of ewes in the soy-enriched diet group were decreased. The area under concentration–time curve AUC (0–24h) was 9.3±4.6 vs. 16.58±4.44μgh/mL in the standard forage or control group. The plasma levels of danofloxacin were unmodified. The AUC (0–24h) milk/plasma ratio decreased by over 50% in the soy-enriched diet group, compared to the control group (4.90±2.65 vs. 9.58±2.17). Exogenous administration of isoflavones did not modify danofloxacin secretion into milk. This study showed that milk excretion of a specific substrate of BCRP, such as danofloxacin, can be diminished by the presence of isoflavones in the diet.

The soy isoflavone genistein inhibits the reduction inAchilles tendon collagen content induced by ovariectomy in rats

The objective of this study was to evaluate the effects of genistein and moderate intensity exercise on Achilles tendon collagen and cross-linking in intact and ovariectomized (OVX) female Sprague-Dawley rats. Rats were separated into eight groups (n = 9/group): intact or OVX, treadmill exercised or sedentary, genistein-treated (300 mg/kg/day) or vehicle. After 6 weeks, tendons were assayed for the collagen-specific amino acid hydroxyproline and hydroxylyslpyridinoline (HP). Collagen content was not influenced by exercise (P = 0.40) but was lower (P < 0.001) in OVX-vehicle rats compared with intact vehicle rats (OVX: 894 ± 35 μg collagen/mg dry weight; intact: 1185 ± 72 μg collagen/mg dry weight). In contrast, collagen content in OVX rats treated with genistein was greater (P = 0.010, 1198 ± 121 μg collagen/mg dry weight) when compared with untreated rats and was not different from intact rats (P = 0.89). HP content was lower in OVX genistein-treated rats when compared with intact genistein-treated rats, but only within the sedentary animals (P = 0.05, intact-treated: 232 ± 39 mmol/mol collagen; OVX-treated: 144 ± 21 mmol/mol collagen). Our findings suggest that ovariectomy leads to a reduction in tendon collagen, which is prevented by genistein. HP content, however, may not have increased in proportion to the addition of collagen. Genistein may be useful for improving tendon collagen content in conditions of estrogen deficiency.

Genistein accelerates refractory wound healing by suppressing superoxide and FoxO1/iNOS pathway in type 1 diabetes

Refractory wounds in diabetic patients constitute a serious complication that often leads to amputation with limited treatment regimens. The present study was designed to determine the protective effect of the soy isoflavone genistein on diabetic wound healing and investigate underlying mechanisms. Streptozotocin (STZ)-induced type 1 diabetic mice with full-thickness excisional wounds received 0.2, 1 or 5mg/kg/day of genistein via subcutaneous injection. Genistein dose-dependently rescued the delay of wound closure in diabetic mice. A dose of 5 mg/kg/day of genistein treatment significantly increased the mean perfusion rate, and in vitro treatment with genistein protected against high glucose-induced impairment of capillary tube formation in cultured endothelial cells. Diabetic conditions significantly increased superoxide anion (O2·−) production and nitrotyrosine formation, and decreased nitrite levels in wound tissues. Genistein treatment at all doses normalized the elevated O2·− production and nitrotyrosine formation, and reversed the attenuated nitrite level. In diabetic wound tissues, the inducible nitric oxide synthase (iNOS) was activated, and genistein administration prevented increased iNOS activity. Moreover, genistein attenuated diabetic cutaneous silent information regulator 1 and forkhead box O transcription factor 1 (FoxO1) levels and potentiated ac-FoxO1 in a dose-dependent manner. Genistein rescued the delayed wound healing and improved wound angiogenesis in STZ-induced type 1 diabetes in mice, at least in part, by suppression of FoxO1, iNOS activity and oxidative stress.

Chemoprotective activity of the isoflavones, genistein and daidzein on mutagenicity induced by direct and indirect mutagens in cultured HTC cells

Isoflavones are phenolic compounds widely distributed in plants and found in a high percentage in soybeans. They have important biological properties and are regarded as potential chemopreventive agents. The aim of this study was to verify the preventive effect of two soy isoflavones (genistein and daidzein) by a micronucleus assay, analysis of GST activity, and real-time RT-PCR analysis of GSTa2 gene expression. Mutagens of direct (doxorubicin) and indirect (2-aminoanthracene) DNA damage were used. Hepatoma cells (HTC) were treated with genistein or daidzein for 26h at noncytotoxic concentrations; 10μM when alone, and 0.1, 1.0 and 10μM when combined with genotoxic agents. The micronucleus test demonstrated that both isoflavones alone had no genotoxic effect. Genistein showed antimutagenic effects at 10μM with both direct and indirect DNA damage agents. On phase II enzyme regulation, the current study indicated an increase in total cytoplasmic GST activity in response to genistein and daidzein at 10μM supplementation. However, the mRNA levels of GSTa2 isozymes were not differentially modulated by genistein or daidzein. The results point to an in vitro antimutagenic activity of genistein against direct and indirect DNA damage-induced mutagenicity.

The soy phytoestrogens genistein and daidzein as neuroprotective agents against anoxia-glucopenia and reperfusion damage in rat urinary bladder

Some bladder disorders, such as obstructive bladder and hyperactivity, may be caused partly by ischemia/reperfusion injury (I/R). The neuroprotective effects of estrogens were demonstrated in in vitro studies and a great interest in soy isoflavones (genistein and daidzein) as alternative to the synthetic estrogen receptor modulators for therapeutic use has been pointed out. The aim of this study was to investigate the effect of genistein and daidzein, on rat detrusor smooth muscle contractility and their possible neuroprotective role against I/R-like condition.Whole rat urinary bladders were subjected to in vitro anoxia-glucopenia (A-G) and reperfusion (R) in the absence or presence of drugs and response to electrical field stimulation (EFS) of intrinsic nerves evaluated. Furthermore rats were treated in vivo for 1week with the phytoestrogens and the same in vitro protocol was applied to the ex vivo bladders. Antioxidant activity of genistein and daidzein on the A-G/R model was determined by measuring malonyldialdehyde (MDA). Moreover, hormones plasma levels were determined by radioimmunoassay.Genistein and daidzein administered either in vitro or in vivo showed significant neuroprotective effect and antioxidant activity. Testosterone and 17β-estradiol plasma levels were not modified by daidzein, while a significant decrease of testosterone in genistein treated rats was evident. Moreover both phytoestrogens significantly decreased detrusor contractions induced by EFS in a concentration-dependent manner. For being either neuroprotective and myorelaxant, genistein and daidzein could be considered a good lead for new therapeutic agents to protect the urinary bladder from hyperactivity and nerve damage.

Phytoestrogens genistein and daidzein affect immunity in the nematode Caenorhabditis elegans via alterations of vitellogenin expression

Phytoestrogens, such as the soy isoflavones genistein and daidzein, are suggested to beneficially affect lipid metabolism in humans and thereby contribute to healthy ageing. New evidences show that phytoestrogens might slow ageing processes also by affecting immune processes. We tested in the nematode Caenorhabditis elegans the effects of 17β-estradiol, genistein, and daidzein on resistance versus the nematode pathogen Photorhabdus luminescens with focus on vitellogenins, which are invertebrate estrogen-responsive genes that encode homologues to ApoB100 with impact on immune functions. Here, we show that the estrogen 17β-estradiol increases the resistance of C. elegans versus P. luminescens by enhancing vitellogenin-expression at the mRNA and protein level. Knockdown of single out of five functional vits by RNA-interference blunted the life-extending effects under heat-stress of 17β-estradiol, demonstrating a lack of redundancy for the vitellogenins. RNAi for nhr-14, a suggested nuclear hormone receptor for estrogens, displayed no influence on 17β-estradiol effects. The soy isoflavone genistein reduced vitellogenin-expression and also resistance versus P. luminescens whereas daidzein increased resistance versus the pathogen in a vitellogenin-dependent manner. Our studies show that induction of estrogen-responsive vitellogenin(s) by the phytoestrogen daidzein potently increases resistance of C. elegans versus pathogenic bacteria and heat whereas genistein acts in an antiestrogenic manner.

Soy Isoflavones Genistein and Daidzein Exert Anti-Apoptotic Actions via a Selective ER-mediated Mechanism in Neurons following HIV-1 Tat1–86 Exposure

BackgroundHIV-1 viral protein Tat partially mediates the neural dysfunction and neuronal cell death associated with HIV-1 induced neurodegeneration and neurocognitive disorders. Soy isoflavones provide protection against various neurotoxic insults to maintain neuronal function and thus help preserve neurocognitive capacity.Methodology/Principal FindingsWe demonstrate in primary cortical cell cultures that 17β-estradiol or isoflavones (genistein or daidzein) attenuate Tat1–86-induced expression of apoptotic proteins and subsequent cell death. Exposure of cultured neurons to the estrogen receptor antagonist ICI 182,780 abolished the anti-apoptotic actions of isoflavones. Use of ERα or ERβ specific antagonists determined the involvement of both ER isoforms in genistein and daidzein inhibition of caspase activity; ERβ selectively mediated downregulation of mitochondrial pro-apoptotic protein Bax. The findings suggest soy isoflavones effectively diminished HIV-1 Tat-induced apoptotic signaling.Conclusions/SignificanceCollectively, our results suggest that soy isoflavones represent an adjunctive therapeutic option with combination anti-retroviral therapy (cART) to preserve neuronal functioning and sustain neurocognitive abilities of HIV-1 infected persons.

Abstract 1988: Increased expression of eukaryotic protein synthesis initiation factor eIF4G by the daidzein metabolite equol may contribute to breast cancer malignancy

Abstract The role of dietary soy in cancer has been the subject of intense investigation and is thought to be cancer preventive. However, the beneficial effects of soy on established breast cancer is controversial. We recently demonstrated that dietary daidzein and combined soy isoflavones (genistein, daidzein, and glycitein) promoted breast cancer progression in a nude mouse model by increasing both primary mammary tumor growth and metastasis. Dietary daidzein significantly upregulated cancer promoting molecules including eukaryotic protein synthesis initiation factors (eIF) eIF4G and eIF4E. Herein, using tumors from mice treated orally with daidzein, we show that increased eIF expression is associated with expression of mRNAs with long structured 5′ untranslated regions and internal ribosomal entry sites (IRES) that are sensitive to eIF4E and eIF4G levels. We then tested the hypothesis that daidzein upregulates protein synthesis initiation in breast cancer, but found that daidzein treatment did not affect the levels of eIFs in the same MDA-MB-435 cell line in vitro. Therefore, we tested the effect of equol that is metabolized from daidzein by the gut bacteria in mice and humans. Results show that equol specifically upregulated eIF4G, but not eIF4E, in MDA-MB-435 and MDA-MB-231 human breast cancer cells. Equol treatment also increased gene and protein expression of c-MYC and protein expression of other cell survival and proliferation promoting molecules with IRES sites. The elevated eIF4G in response to equol was not associated with eIF4E in a cap binding co-capture assay. Therefore, upregulation of eIF4G by equol may regulate cap-independent protein synthesis initiation resulting in cancer cell survival, proliferation, and thus, tumor progression. This research was supported by grant numbers US Army/BCRP W81XWH-11-1-0199 to CD, to NIH/NIGMS SC3GM084824 to SD Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1988. doi:1538-7445.AM2012-1988

Abstract LB-167: Prepubertal or lifetime genistein intake reduces risk of tamoxifen resistance in rats

Abstract Using a preclinical model, we studied whether consumption of soy isoflavone genistein (GEN) during childhood modifies the effect of adult GEN intake on the ability of tamoxifen (TAM) to inhibit mammary tumor growth. Female rats were fed AIN93G control diet supplemented with 0 or 500 ppm genistein between postnatal days (PND) 15 and 30 (prepubertal exposure); on PND30 both groups received control diet. They were then exposed on PND50 to DMBA, and on PND57 divided to four dietary groups (n=20-40 per group) (see Table). Most rats in all four groups developed mammary tumors, but tumor latency was longer in the prepubertally GEN fed G-G (P&amp;lt;0.003) and G-C groups (p&amp;lt;0.095), compared to controls. TAM treatment (338 ppm in the diet) was started when tumor reached a size of 1.4 cm, and rats were followed for 18 weeks. The response to TAM was determined as complete response (CR), partial response (PR), or as being resistant. Adding GEN to the diet when TAM treatment started increased TAM resistance by 48%, compared to rats which were never fed GEN. Adult GEN intake (C-G group) further reduced CR. However, protein levels in the tumors of genes involved in unfolded-protein response and associated with TAM resistance (IRE1a, BIP, ATF4, BECLIN1, CHOP, ER), were not affected. Prepubertal GEN intake in G-C and G-G groups significantly increased the rate of CR and inhibited TAM resistance. Total tumor burden, which reflects the response of all tumors per rat to TAM, including those appearing during TAM treatment (de novo TAM resistant) was significantly higher in the rats which received GEN as adults, compared to the other three groups (p&amp;lt;0.001); lowest tumor burden was seen in the rats which consumed GEN both during prepuberty and as adults. Our findings suggest that prepubertally GEN fed rats, also when they continue to consume GEN in adulthood, are at low risk of developing TAM resistance. In contrast, adult only GEN consumption significantly impaired response to TAM. Mechanisms explaining these data are currently being investigated. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-167. doi:1538-7445.AM2012-LB-167

Genistein‐mediated inhibition of mammary stromal adipocyte differentiation limits expansion of mammary stem/progenitor cells by paracrine signaling

Mammary adiposity may contribute to breast cancer development and progression by releasing cytokines and other inflammatory mediators that promote mammary epithelial proliferation. We evaluated the effects of soy isoflavone genistein (GEN) on the adipogenic differentiation of a SV40‐immortalized mouse mammary stromal fibroblast like cells (MSF) treated with differentiating agents insulin, hydrocortisone and troglitazone (DM). MSF cultured in DM with and without extracellular matrix for 14 days showed reduced differentiation (2–3 fold) into mature adipocytes with 40nM but not 2uM GEN, as evaluated by Oil Red O staining. Addition of sera from GEN‐fed adult mice to MSF similarly reduced adipogenic differentiation (4–5 fold), relative to sera from casein‐fed mice. Lipid accumulation was decreased by GEN (40nM&gt;2uM). Expression levels of lipogenic enzyme genes fatty acid synthase and PPAR‐γ were down‐regulated by 40nM GEN. Estrogen receptor (ER)‐β, an inhibitor of PPAR‐γ transcriptional activity, but not ER‐α transcript levels were increased by 40 nM GEN. Conditioned media from GEN‐treated MSF reduced anchorage‐independent mammosphere formation of human breast cancer cells MCF‐7. Thus, dietary factor control of mammary adiposity, possibly mediated by ER‐β, may limit mammary stem/progenitor cell expansion and protect against breast cancer.Grant Funding Source: USDA‐CRIS 6251‐5100002‐06S; CUMG/ACHRI

In Utero and Lactational Exposure to Low-Dose Genistein-Vinclozolin Mixture Affects the Development and Growth Factor mRNA Expression of the Submandibular Salivary Gland in Immature Female Rats

It has been suggested that hormonally controlled submandibular salivary gland (SSG) development and secretions may be affected by endocrine disruptor compounds. We investigated the effects of oral gestation-lactation exposure to 1 mg/kg body weight daily dose of the estrogenic soy-isoflavone genistein and/or the anti-androgenic food contaminant vinclozolin in female rats. The SSGs of female offspring were collected at postnatal day 35 to study gland morphogenesis and mRNA expression of sex-hormone receptors and endocrine growth factors as sex-dependent biomarkers. Because of high expression in neonatal SSG, mRNA expression of transforming growth factor α was also studied. Exposure to genistein, vinclozolin, or a genistein+vinclozolin mixture resulted in significantly lower numbers of striated ducts linked to an increase in their area and lower acinar proliferation (Ki-67-positive nuclei). Exposure to the mixture had the highest significant effects, which were particularly associated with repression of epidermal growth factor, nerve growth factor, and transforming growth factor α expression. In conclusion, early exposure to low doses of genistein and vinclozolin can affect glandular structure and endocrine gene mRNA expression in prepubertal SSG in female rats, and the effects are potentialized by the genistein+vinclozolin mixture. Our study provides the first evidence that SSG are targeted by both estrogenic and anti-androgenic disrupting compounds and are more sensitive to mixtures.

Repression of mammosphere formation of human breast cancer cells by soy isoflavone genistein and blueberry polyphenolic acids suggests diet-mediated targeting of cancer stem-like/progenitor cells

Mammary stem cells are undifferentiated epithelial cells, which initiate mammary tumors and render them resistant to anticancer therapies, when deregulated. Diets rich in fruits and vegetables are implicated in breast cancer risk reduction, yet underlying mechanisms are poorly understood. Here, we addressed whether dietary factors selectively target mammary epithelial cells that display stem-like/progenitor subpopulations with previously recognized tumor-initiating potential. Using estrogen receptor-positive MCF-7 and estrogen receptor-negative MDA-MB-231 human breast cancer cell lines and freshly isolated epithelial cells from MMTV-Wnt-1 transgenic mouse mammary tumors, we demonstrate that sera of adult mice consuming soy isoflavone genistein (GEN) or blueberry (BB) polyphenol-containing diets alter the population of stem-like/progenitor cells, as measured by their functional ability to self-renew and form anchorage-independent spheroid cultures in vitro at low frequency (1-2%). Serum effects on mammosphere formation were dose-dependently replicated by GEN (40 nM >2 μM) and targeted the basal stem-like CD44+/CD24-/ESA+ and the luminal progenitor CD24+ subpopulations in MDA-MB-231 and MCF-7 cells. GEN inhibition of mammosphere formation was mimicked by the Akt inhibitor perifosine and was associated with enhanced tumor suppressor phosphatase and tensin homologue deleted on chromosome ten (PTEN) expression. In contrast, a selected mixture of BB phenolic acids was only active in MDA-MD-231 cells and its CD44+/CD24-/ESA+ subpopulation, and this activity was independent of induction of PTEN expression. These findings delineate a novel and selective function of distinct dietary factors in targeting stem/progenitor cell populations in estrogen receptor-dependent and -independent breast cancers.

Soy isoflavone Genistein affects energy metabolism in a steatotic liver model

Non-alcoholic fatty liver disease (NAFLD) is already the most common chronic liver disease in western countries. The complex metabolic disorder is strongly associated with insulin resistance. Epidemiological studies suggest beneficial effects of the natural soy isoflavone Genistein (GEN) on hepatic energy metabolism. Our aim was to establish a steatotic liver in vitro model to investigate the impact of GEN on energy metabolism focused on insulin signaling. Primary human hepatocytes (PHH) were isolated from resected liver tissues via a two-step collagenase perfusion technique. Steatosis was induced by adding oleic and palmitic acid for 24h to the culture medium. The lipid content was determined photometrically by Oil Red O and SRB staining. Cytotoxicity was evaluated by assays of XTT, AST/LDH and UREA. Phosphorylation levels of ERK½, AKT, FOXO1 and GSK3α/β were measured by Western blot analysis in PHH with and without insulin as well as after incubation with GEN for 24h. PHH treated with free fatty acids showed a significant increase of fat accumulation and a moderate lipotoxicity. Furthermore, in steatotic PHH we observed decreased insulin induced phosphorylation levels of ERK½, AKT, FOXO1 and GSK3α/β. Additional treatment with GEN showed in control PHH an increase of insulin induced phoshorylation levels of ERK½, AKT and GSK3α/β whereas steatotic PHH revealed decreased levels of ERK½ and AKT in a dose dependent manner. Our data show that the steatotic liver in vitro model is a reliable reproduction of in vivo conditions regarding fat accumulation, insulin resistance and lipotoxicity. Insulin resistance was observed by an impaired phosphorylation of ERK½, AKT, FOXO1 and GSK3α/β. GEN leads only in control PHH to an improvement of insulin signaling by increasing phosphorylation levels. However, in steatotic PHH a beneficial effect was not observed. Therefore we recommend further studies to investigate the impact of GEN on energy metabolism in steatotic liver.

Soy Isoflavones and Other Isoflavonoids Activate the Human Bitter Taste Receptors hTAS2R14 and hTAS2R39

The aim of this study was to identify the bitter receptor(s) that recognize the bitter taste of the soy isoflavone genistein. Screening of all 25 human bitter receptors revealed genistein as agonist of hTAS2R14 and hTAS2R39. Genistein displayed threshold values of 4 and 8 μM on hTAS2R14 and hTAS2R39 and EC(50) values of 29 and 49 μM, respectively. In addition, the behavior of structurally similar isoflavonoids was investigated. Although the two receptors are not closely related, the results for hTAS2R14 and hTAS2R39 were similar toward most isoflavonoid aglycones. By trend, threshold values were slightly lower on hTAS2R14. Glucosylation of isoflavones seemed to inhibit activation of hTAS2R14, whereas four of five glucosylated isoflavones were agonists of hTAS2R39, namely, glycitin, genistin, acetylgenistin, and malonylgenistin. A total of three hydroxyl substitutions of the A- and B-rings of the isoflavonoids seemed to be more favorable for receptor activation than fewer hydroxyl groups. The concentration of the trihydroxylated genistein in several soy foods exceeds the determined bitter receptor threshold values, whereas those of other soy isoflavones are around or below their respective threshold value. Despite its low concentration, genistein might be one of the main contributors to the bitterness of soy products. Furthermore, the bioactive isoflavonoids equol and coumestrol activated both receptors, indicating that their sensory impact should be considered when used as food ingredients.

Genistein induces breast cancer-associated aromatase and stimulates estrogen-dependent tumor cell growth in in vitro breast cancer model

In breast cancer, the interaction between estrogen-producing breast adipose fibroblasts (BAFs) and estrogen-dependent epithelial tumor cells is pivotal. Local estrogen production is catalyzed by aromatase, which is differentially regulated in disease-free and tumorigenic breast tissue. The use of aromatase inhibitors to block local estrogen production has proven effective in treatment of estrogen-dependent breast cancer. However, a major problem during breast cancer treatment is the sudden onset of menopause and many women seek for alternative medicines, such as the soy isoflavone genistein. In this study, we show that genistein can induce estrogen-dependent MCF-7 tumor cell growth and increase breast cancer-associated aromatase expression and activity in vitro. We have previously developed an in vitro breast cancer model where the positive feedback loop between primary BAFs and estrogen-dependent MCF-7 tumor cells is operational, thereby representing a more natural in vitro model for breast cancer. In this model, genistein could negate the growth inhibitory action of the aromatase inhibitor fadrozole at physiologically relevant concentrations. These data suggest that soy-based supplements might affect the efficacy of breast cancer treatment with aromatase inhibitors. Considering the high number of breast cancer patients using soy supplements to treat menopausal symptoms, the increasing risk for adverse interactions with breast cancer treatment is of major concern and should be considered with care.

Repression of mammosphere formation in breast cancer cells by soy isoflavone genistein and blueberry polyphenols

Epidemiological evidence implicates diets rich in fruits and vegetables in breast cancer prevention due to their phytochemical components, yet mechanisms for their anti-tumor activities are not well-understood. A small population of mammary epithelial cells, termed cancer stem cells (CSC), may be responsible for initiating and sustaining tumor development. To evaluate dietary components that selectively target CSC and thus, provide mammary tumor protection, we utilized the estrogen receptor (ER)-positive MCF-7 and ER-negative MDA-MB231 human breast cancer cell lines. Within 5 days of culture, both cell lines formed mammospheres at a frequency (1–2%) consistent with a subset of the cell population exhibiting stem cell-like characteristics. The soy isoflavone genistein dose-dependently decreased (40 nM > 2 μM) mammosphere numbers from both cell lines, relative to medium alone. A mixture of phenolic acids that include hippuric acid, ferrulic acid and 3-hydroxycinnamic acid, based on concentrations found in sera of rats fed diets containing 10% blueberry similarly inhibited mammosphere formation in MDA-MB231 but not in MCF-7 cells. By contrast, leptin and interleukin-6 had no activity in these cells. Results suggest that dietary factors may selectively target ER-positive and ER-negative cancer cells with stem-like properties in the prevention of breast cancer. [USDA-CRIS; Department of Defense BCRP]

Additive effects of trastuzumab and genistein on human breast cancer cells

Soy isoflavone genistein, a tyrosine kinase inhibitor and agonist of estrogen receptor-β (ERβ), is known to have antitumoral properties. Given that ERβ often is coexpressed with HER2 in breast cancer, both functions of genistein might be able to enhance the antitumoral action of trastuzumab. In this in-vitro study, we tested whether combined treatment with genistein and trastuzumab exerts additive effects on breast cancer cells. HER2-overexpressing breast cancer cell lines were treated with genistein alone and in combination with trastuzumab. The effects of this treatment on proliferation and gene expression were analyzed. Treatment with high-dose genistein (10 μmol/l) significantly increased the growth-inhibitory effect of trastuzumab on HER2-overexpressing, ERα/β-positive BT-474 breast cancer cells. Combinatory treatment using lower doses of trastuzumab exerted similar effects as a single treatment with standard doses of this drug. In contrast, this effect was absent in ERα-negative SK-BR-3 cells. Similar results were obtained after cotreatment with the ERβ agonist, 2,3-bis(4-hydroxyphenyl)propionitrile. The growth-inhibitory effect of both drugs was accompanied by an increased expression of the putative tumor suppressor ERβ variant, cx, and their combination further elevated mRNA levels of this receptor. In conclusion, genistein significantly enhanced the antitumoral effect of trastuzumab on BT-474 breast cancer cells in vitro. The relevance of these data particularly for women with HER2-overexpressing and ERα/β-positive breast cancer has to be verified in animal or clinical studies.

Protective Effect of Soy Isoflavone Genistein on Ischemia-Reperfusion in the Rat Small Intestine

Ischemia-reperfusion (I/R) injury of the intestine is an important factor associated with high rates of morbidity and mortality. Intestinal I/R is a common clinical problem in the settings of severe burns, circulatory shock and strangulation ileus. Intestinal I/R damages remote organs and promotes multi-organ failure. It has been shown that enteral feeding before ischemic insults is beneficial for reducing organ injury and improving survival after intestinal I/R. In that study, the authors used a standard complex enteral diet and they suggested that it is important to find new nutrient formulas. Since reactive oxygen species are responsible for intestinal I/R injury, we focused on a dietary polyphenol, the soy isoflavone genistein. Genistein has a wide spectrum of biochemical and pharmacological activities. However, the possibility of a protective effect of genistein as enteral nutrition on I/R injury has not been investigated. We therefore investigated the protective effect of genistein on oxidative injury using intestinal I/R model rats. We found that genistein, which has combined antioxidant activity from radical scavenging, xanthine oxidase inhibition and chain-breaking effects, exhibits a protective effect on intestinal I/R injury. The results suggest that genistein, a soy isoflavone, has the possibility as a new nutrient formula of enteral feeding.