Effect of phytoestrogens on basal and GnRH-induced gonadotropin secretion

Plant-derived estrogens (phytoestrogens, PEs), like endogenous estrogens, affect a diverse array of tissues, including the bone, uterus, mammary gland, and components of the neural and cardiovascular systems. We hypothesized that PEs act directly at pituitary loci to attenuate basal FSH secretion and increase gonadotrope sensitivity to GnRH. To examine the effect of PEs on basal secretion and total production of FSH, ovine pituitary cells were incubated with PEs for 48 h. Conditioned media and cell extract were collected and assayed for FSH. Estradiol (E₂) and some PEs significantly decreased basal secretion of FSH. The most potent PEs in this regard were coumestrol (CM), zearalenone (ZR), and genistein (GN). The specificity of PE-induced suppression of basal FSH was indicated by the absence of suppression in cells coincubated with PEs and an estrogen receptor (ER) blocker (ICI 182 780; ICI). Secretion of LH during stimulation by a GnRH agonist (GnRH-A) was used as a measure of gonadotrope responsiveness. Incubation of cells for 12 h with E₂, CM, ZR, GN, or daidzein (DZ) enhanced the magnitude and sensitivity of LH secretion during subsequent exposure to graded levels of a GnRH-A. The E₂- and PE-dependent augmentation of gonadotrope responsiveness was nearly fully blocked during coincubation with ICI. Collectively, these data demonstrate that selected PEs (CM, ZR, and GN), like E₂, decrease basal secretion of FSH, reduce total FSH production, and enhance GnRH-A-induced LH secretion in a manner that is dependent on the ER.

Effects of sodium selenite and germination on the sprouting of chickpeas (Cicer arietinum L.) and its content of selenium, formononetin and biochanin A in the sprouts

To improve the nutritional value of chickpea food, selenium (Se)-rich chickpea sprouts were produced by germination of chickpea seeds for 6 days at 28 centigrade in the presence of various concentrations of Na(2)SeO(3) in germination solution. High concentrations of selenite were found to inhibit the growth of chickpea sprout and the biosynthesis of isoflavones formononetin and biochanin A. However, chickpea sprouts could tolerate up to ~50 mg/L of Na(2)SeO(3), under which condition the product chickpea sprouts contained a high Se content (2.14 μg/g dry weight) and a moderate high content of isoflavones (601.56 μg biochanin A/g dry weight and 578.11 μg formononetin/g dry weight). Se was incorporated in chickpea sprout in the form of selenomethionine. Thus, Se-enriched chickpea sprouts may serve as a convenient dietary source of Se and of isoflavones, including formononetin and biochanin A.

Soy isoflavone genistein induces cell death in breast cancer cells through mobilization of endogenous copper ions and generation of reactive oxygen species

SCOPE

Worldwide geographical variation in cancer incidence indicates a correlation between dietary habits and cancer risk. Epidemiological studies have suggested that populations with high isoflavone intake through soy consumption have lower rates of breast, prostate, and colon cancer. Isoflavone genistein in soybean is considered a potent chemopreventive agent against cancer. Although several mechanisms have been proposed, a clear anticancer action mechanism of genistein is still not known.

METHODS AND RESULTS

Here, we show that the cytotoxic action of genistein against breast cancer cells involves mobilization of endogenous copper. Further, whereas the copper specific chelator neocuproine is able to inhibit the apoptotic potential of genistein, the molecules which specifically bind iron (desferroxamine mesylate) and zinc (histidine) are relatively ineffective in causing such inhibition. Also, genistein-induced apoptosis in these cells is inhibited by scavengers of reactive oxygen species (ROS) implicating ROS as effector elements leading to cell death.

CONCLUSIONS

As copper levels are known to be considerably elevated in almost all types of cancers, in this proof-of-concept study we show that genistein is able to target endogenous copper leading to prooxidant signaling and consequent cell death. We believe that such a mechanism explains the anticancer effect of genistein as also its preferential cytotoxicity towards cancer cells.

Prothoracicotropic hormone induces tyrosine phosphorylation in prothoracic glands of the silkworm, Bombyx mori

In the present study, we investigated the tyrosine phosphorylation of Bombyx mori prothoracic glands using phosphotyrosine-specific antibodies and Western blot analysis. Results showed that prothoracicotropic hormone (PTTH) stimulates a rapid increase in tyrosine phosphorylation of at least 2 proteins in prothoracic glands, one of which was identified as extracellular signal-regulated kinase (ERK). The phosphorylation of another 120-kDa protein showed dose- and time-dependent stimulation by PTTH in vitro. In vitro activation of tyrosine phosphorylation was also verified by in vivo experiments: injection of PTTH into day-6 last-instar larvae greatly increased tyrosine phosphorylation. Treatment of prothoracic glands with the protein tyrosine phosphatase inhibitor, sodium orthovanadate, also resulted in tyrosine phosphorylation of several proteins and increased ecdysteroidogenesis. The PTTH-stimulated phosphorylation of the 120-kDa protein was markedly attenuated by genistein, a broad-spectrum tyrosine kinase inhibitor, but not by HNMPA-(AM)(3) , a specific inhibitor of insulin receptor tyrosine kinase. PP2, a more-selective inhibitor of the Src-family tyrosine kinases, partially inhibited PTTH-stimulated tyrosine phosphorylation, but not ecdysteroidogenesis. This result implies the possibility that in addition to ERK, the phosphorylation of the 120-kDa protein, which is not Src-family tyrosine kinase, is likely also involved in PTTH-stimulated ecdysteroidogenesis in B. mori.

Mechanical stretch activates signaling events for protein translation initiation and elongation in C2C12 myoblasts

It has been proposed that mechanically induced tension is the critical factor in the induction of muscle hypertrophy. However, the molecular mechanisms involved in this process are still under investigation. In the present study, the effect of mechanical stretch on intracellular signaling for protein translation initiation and elongation was studied in C2C12 myoblasts. Cells were grown on a silicone elastomer chamber and subjected to 30-min of 5 or 15% constant static or cyclic (60 cycles/min) uniaxial stretch. Western blot analyses revealed that p70 S6 kinase (p70S6K) and eukaryotic elongation factor 2 (eEF2), which are the markers for translation initiation and peptide chain elongation, respectively, were activated by both static and cyclic stretch. The magnitude of activation was greater in response to the 15% cyclic stretch. Cyclic stretch also increased the phosphorylation of MAP kinases (p38 MAPK, ERK1/2 and JNK). However, the pharmacological inhibition of MAP kinases did not block the stretch-induced activation of p70S6K and eEF2. An inhibitor of the mammalian target of rapamycin (mTOR) blocked the stretch-induced phosphorylation of p70S6K but did not affect the eEF2 activation. A broad-range tyrosine kinase inhibitor, genistein, blocked the stretch-induced activation of p70S6K and eEF2, whereas Src tyrosine kinase and Janus kinase (JAK) inhibitors did not. These results suggest that the stretch-induced activation of protein translation initiation and elongation in mouse myoblast cell lines is mediated by tyrosine kinase(s), except for Src kinase or JAK.

Lycopene and other carotenoids inhibit estrogenic activity of 17beta-estradiol and genistein in cancer cells

Epidemiological evidence suggests that carotenoids prevent several types of cancer, including mammary and endometrial cancers. On the other hand, such studies have also shown that estrogens are the most important risk factors for these cancer types. Genistein, the phytoestrogen mainly found in soy, also shows significant estrogenic activity when tested at concentrations found in human blood. The aim of this study was to determine whether carotenoids inhibit signaling of steroidal estrogen and phytoestrogen which could explain their cancer preventive activity. Similar to the known effect of 17beta-estradiol (E(2)), treatment of breast (T47D and MCF-7) and endometrial (ECC-1) cancer cells with phytoestrogens induced cell proliferation, cell-cycle progression and transactivation of the estrogen response element (ERE). However, each of the tested carotenoids (lycopene, phytoene, phytofluene, and beta-carotene) inhibited cancer cell proliferation induced by either E(2) or genistein. The inhibition of cell growth by lycopene was accompanied by slow down of cell-cycle progression from G1 to S phase. Moreover, the carotenoids inhibited estrogen-induced transactivation of ERE that was mediated by both estrogen receptors (ERs) ERalpha and ERbeta. The possibility that this inhibition results from competition of carotenoid-activated transcription systems on a limited pool of shared coactivators with the ERE transcription system was tested. Although cotransfection of breast and endometrial cancer cells with four different coactivators (SRC-1, SRC-2, SRC-3, and DRIP) strongly stimulated ERE reporter gene activity, it did not oppose the inhibitory effect of carotenoids. These results suggest that dietary carotenoids inhibit estrogen signaling of both 17beta-estradiol and genistein, and attenuate their deleterious effect in hormone-dependent malignancies.

Effects of estrogenic xenobiotics on human and mouse spermatozoa

OBJECTIVE

To investigate human sperm responsiveness to the estrogenic xenobiotic genistein and seek further information regarding the mechanism of action of estrogenic xenobiotics using mouse spermatozoa.

METHODS

Uncapacitated human spermatozoa were incubated with genistein and assessed using chlortetracycline (CTC) fluorescence. CTC was also used to evaluate mouse sperm responses to daidzein and combinations of genistein, 8-prenylnaringenin and nonylphenol. Several steroids were tested to determine structure-function relationships, and possible involvement of cAMP and G proteins in responses was also investigated.

RESULTS

Genistein significantly accelerated capacitation and acrosome loss in human spermatozoa, with 1, 10 and 100 nmol/l being equally effective. In mouse spermatozoa, daidzein produced significant responses, and combinations of xenobiotics at low concentrations were more effective than used singly. The compounds appear to act at the cell surface, and responses to three different steroids were nonidentical. A protein kinase-A inhibitor blocked responses to xenobiotics, while genistein and nonylphenol significantly stimulated cAMP production. Pertussis toxin and dideoxyadenosine blocked responses, suggesting involvement of inhibitory G proteins and membrane-associated adenylyl cyclases.

CONCLUSION

Human and mouse sperm responses to genistein are very similar, but human gametes appear to be even more sensitive. The mechanism of action may involve unregulated stimulation of cAMP production, leading to significant acrosome loss, undesirable because already acrosome-reacted cells are nonfertilizing. Xenobiotics were even more effective in combination. Since simultaneous exposure to low concentrations of multiple xenobiotics is likely to occur in animals and humans, further investigation is needed to determine whether this could impair fertility.

Reduction of genistein clastogenicity in Chinese hamster V79 cells by daidzein and other flavonoids

A broad spectrum of health benefits has been ascribed to soy products. These products contain soy protein and relatively high levels of polyphenolic compounds known as flavonoids. While they are the most likely candidates for biological activity, flavonoids as a class, and of specific interest, genistein, are well known to be genotoxic due to their ability to "poison" cellular DNA topoisomerase II (topo II) resulting in stable chromosome breakage and mutation and raising questions about the long term health effects associated with chronic flavonoid exposure. Interestingly, some flavonoids, such as biochanin, galangin and daidzein, are catalytic topo II inhibitors (not poisons) and actually antagonize the clastogenicity of topo II poisons. It is shown in the present paper that flavonoids possessing catalytic topo II inhibitory activity, strongly antagonize the clastogenicity of genistein in Chinese hamster V79 cells. Importantly, one of these, daidzein, is a major constituent of marketed soy products. It is conjectured that the potential human clastogenic risk of soy products containing genistein might be mitigated or abolished due to the presence of daidzein or other flavonoids in those products.

Assessment of the estrogenicity of isoflavonoids, using MCF-7-ERE-Luc cells

In the current study, our research focused on the estrogenic activity of isoflavonoids, mainly genistein, biochanin A and daidzein. Genistein enhanced the reporter gene expression of MCF-7-ERE-Luc cells, at a concentration as low as 10 nM, with a concentration of 100 nM the achieved gene expression effects were similar to those of 10 pM 17beta-estradiol, Based on the estrogenic activities of biochanin A and daidzein, hydroxyl groups at the 4' and 5 positions are needed for the maximal effect of the genistein. The estrogenic effects of these isoflavonoids were inhibited by the concomitant treatment with tamoxifen. The data showed that the estrogenic effects of isoflavonoids were mediated through estrogen receptors. When the isoflavonoids were tested as mixtures, the estrogenic effects were lower than the arithmetic sum of those induced by each individual isoflavonoid. The estrogenic potency of each isoflavonoid was presented at EC50 levels with a 17beta-estradiol equivalent concentration (EEQ) based on the dose response of each chemical. The EC50s and EEQs of genistein, biochanin A and daidzein were 4.15, 0.89 and 0.18 microM, and 15.0, 5.12 and 1.83 microM/M, respectively. Our data clearly demonstrated that the pERE-luciferase reporter gene assay was suited for the sensitive and quantitative measurement, and large scale screening, of the estrogenicity of chemicals in vitro.

NAD(P)H oxidase activation by angiotensin II is dependent on p42/44 ERK-MAPK pathway activation in rat's vascular smooth muscle cells

OBJECTIVE

To determine whether the activation of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase and the increase of superoxide anion production by angiotensin II is dependent upon the activation of the ERK-MAPK pathway.

METHODS

Hypertension was induced in Sprague-Dawley rats by infusing angiotensin II (200 ng/kg per min) through osmotic pumps for 12 days. The effects of treatments including an angiotensin II type 1 (AT(1)) blocker losartan (20 mg/kg per day), a tyrosine kinase inhibitor genistein (1.6 microg/kg per min), a specific ERK-MAPK inhibitor, PD98059 (2 mg/kg per day) and an antioxidant alpha-lipoic acid (500 mg/kg of chow) were evaluated during angiotensin infusion. The aortic superoxide anion production, the ERK-MAPK pathway activity and the systolic blood pressure (SBP), were measured following those treatments.

RESULTS

Increases in the concentration of the superoxide anion (1622 to 3719 cpm), in NAD(P)H activity (107%) and in the ERK-MAPK activity (3.6-fold) in the aorta as well as a rise in the arterial pressure (136 to 184 mmHg) were observed 12 days after initiating the treatments (P < 0.05). When the angiotensin-treated rats were treated either with losartan, genistein, PD98059 or alpha-lipoic acid, increases in superoxide anion production, in NAD(P)H oxidase activity, in ERK-MAPK activity and in blood pressure were attenuated. A correlation between the superoxide anion production and the ERK-MAPK activity was also observed.

CONCLUSIONS

The present study suggests that the NAD(P)H-dependent increase of the superoxide anion production in the vascular tissue following a treatment with angiotensin II is dependent on the activation of the ERK-MAPK pathway.

Calcium-sensitive potassium channel inhibitors antagonize genistein- and daidzein-induced arterial relaxation in vitro

Estradiol-17beta relaxes rabbit coronary artery rings via large conductance Ca2+-activated K+-channels (K(Ca)). Genistein and daidzein are plant-derived estrogen-like compounds. The aim of the present study was to investigate whether potassium channels participate in the genistein- and daidzein-induced arterial relaxation like they do in the case of estradiol-17beta. Endothelium-denuded superior mesenteric arterial rings from non-pregnant Wistar female rats were used. At a concentration of 10 microM, estradiol-17beta, genistein and daidzein relaxed noradrenaline precontracted arterial rings, (58 +/- 4%, 45 +/- 5% and 31 +/- 3%, respectively; (n=6-8)). Genistein- and daidzein-induced relaxations were inhibited both by iberiotoxin (1-10 nM) and charybdotoxin (30 nM), the antagonists of large conductance Ca2+-activated K+-channels (K(Ca)). Estradiol-17beta-induced relaxation was reduced by iberiotoxin (30 nM). Estradiol-17beta- and daidzein-induced relaxations were also decreased by apamin (0.1-0.3 microM), an antagonist of small conductance Ca2+-activated K+-channels. The antagonists of voltage-dependent K+-channels (K(V)) (4-aminopyridine), ATP-sensitive K+-channels (K(ATP)) (glibenclamide), or inward rectifier K+-channels (KIR) (barium) had no effect on the relaxation responses of any of the compounds studied. Estrogen receptor antagonist tamoxifen did not inhibit the relaxations. In conclusion, in the noradrenaline precontracted rat mesenteric arteries, the relaxations caused by estradiol-17beta, genistein and daidzein were antagonized by large and small conductance K(Ca)-channel inhibitors, suggesting the role of these channels as one of the relaxation mechanisms.

Genistein and curcumin block TGF-beta 1-induced u-PA expression and migratory and invasive phenotype in mouse epidermal keratinocytes

Transforming growth factor-beta 1 (TGF-beta 1) stimulates migration/invasion of mouse transformed keratinocytes and increases urokinase (u-PA) expression/secretion. In this report, we analyzed the biological behavior of two naturally occurring inhibitors of protein tyrosine kinases, genistein and curcumin, that could abrogate the enhancement of u-PA levels induced by TGF-beta 1 in transformed keratinocytes. Our results showed that genistein and curcumin blocked this response in a dose-dependent manner and also inhibited the TGF-beta 1-induced synthesis of fibronectin, an early responsive gene to the growth factor. Both compounds also reduced TGF-beta 1-stimulated cell migration and invasiveness. These results suggest that a tyrosine kinase-signaling pathway should be involved in TGF-beta 1-mediated increased malignancy of transformed keratinocytes and that genistein and curcumin could play an important role in inhibiting tumor progression.

Galectin-3 mediates genistein-induced G(2)/M arrest and inhibits apoptosis

Many recent studies have focused on potential chemopreventive activities of dietary genistein, a natural isoflavonoid compound found in soy products. Genistein has been implicated in anticancer activities, including differentiation, apoptosis, inhibition of cell growth and inhibition of angiogenesis. In previous studies, genistein was shown to induce apoptosis and cell cycle arrest at G(2)/M in several cancer cell lines in vitro, which is associated with induction of p21(WAF1/CIP1), a universal inhibitor of cyclin-dependent kinases. At present, the molecular basis for diverse genistein-mediated cellular responses is largely unknown. In the present study, we investigated whether galectin-3, an anti-apoptotic gene product, regulates genistein-mediated cellular responses. We show that genistein effectively induces apoptosis without detectable cell cycle arrest in BT549, a human breast epithelial cell line which does not express galectin-3 at a detectable level. In galectin-3 transfected BT549 cells, genistein induced cell cycle arrest at the G(2)/M phase without apoptosis induction. Interestingly, genistein induces p21(WAF1/CIP1) expression in galectin-3-expressing BT549 cells, but not in control BT549 cells undergoing apoptosis. Collectively, the results of the present study suggest that galectin-3, at least in part, is a critical determinant for genistein-mediated cell cycle arrest and apoptosis, and genistein induction of p21(WAF1/CIP1) is associated with cell cycle arrest, but not required for apoptosis induction.

Noncatalytic inhibition of cyclic nucleotide-gated channels by tyrosine kinase induced by genistein

Rod photoreceptor cyclic nucleotide-gated (CNG) channels are modulated by tyrosine phosphorylation. Rod CNG channels expressed in Xenopus oocytes are associated with constitutively active protein tyrosine kinases (PTKs) and protein tyrosine phosphatases that decrease and increase, respectively, the apparent affinity of the channels for cGMP. Here, we examine the effects of genistein, a competitive inhibitor of the ATP binding site, on PTKs. Like other PTK inhibitors (lavendustin A and erbstatin), cytoplasmic application of genistein prevents changes in the cGMP sensitivity that are attributable to tyrosine phosphorylation of the CNG channels. However, unlike these other inhibitors, genistein also slows the activation kinetics and reduces the maximal current through CNG channels at saturating cGMP. These effects occur in the absence of ATP, indicating that they do not involve inhibition of a phosphorylation event, but rather involve an allosteric effect of genistein on CNG channel gating. This could result from direct binding of genistein to the channel; however, the time course of inhibition is surprisingly slow (>30 s), raising the possibility that genistein exerts its effects indirectly. In support of this hypothesis, we find that ligands that selectively bind to PTKs without directly binding to the CNG channel can nonetheless decrease the effect of genistein. Thus, ATP and a nonhydrolyzable ATP derivative competitively inhibit the effect of genistein on the channel. Moreover, erbstatin, an inhibitor of PTKs, can noncompetitively inhibit the effect of genistein. Taken together, these results suggest that in addition to inhibiting tyrosine phosphorylation of the rod CNG channel catalyzed by PTKs, genistein triggers a noncatalytic interaction between the PTK and the channel that allosterically inhibits gating.

Anabolic effect of genistein on bone metabolism in the femoral-metaphyseal tissues of elderly rats is inhibited by the anti-estrogen tamoxifen

Whether the anabolic effect of genistein on bone metabolism in the femoral-metaphyseal tissues of elderly rats is inhibited by the anti-estrogen tamoxifen was investigated in vitro. Bone tissues were cultured for 24 h in the medium containing either vehicle or genistein. The presence of genistein (10(-6) and 10(-5) M) caused a significant increase in calcium content, alkaline phosphatase activity and DNA content in the bone tissues. The effect of genistein (10(-5) M) in increasing bone alkaline phosphatase activity and DNA content was equal to the stimulatory effect of 17 beta-estradiol (10(-10) and 10(-9) M) on the bone components. The genistein effect was not significantly enhanced by the presence of 17 beta-estradiol (10(-10) and 10(-9) M). The anti-estrogen tamoxifen (10(-7) M) completely blocked the effect of 17 beta-estrogen in increasing bone alkaline phosphatase activity and DNA content. The genistein (10(-5) M)-induced increases in bone alkaline phosphatase activity and DNA content were completely abolished by the presence of tamoxifen (10(-7) and 10(-6) M), although tamoxifen itself had no effect on the bone components. The present study demonstrated that the anabolic effect of genistein on bone components is inhibited by anti-estrogen tamoxifen. The effect of genistein may be mediated through estrogen-like action.