Inhibition of cellular phosphatidylinositol turnover by psi-tectorigenin

Effects of phyto-oestrogens on tissues

Recent investigations on the effects of phyto-oestrogens on various tissues have revealed that these diverse molecules may improve human health, particularly by protecting against certain chronic diseases. After a brief examination of the food sources, structures, and general cellular actions of the major phyto-oestrogens, current research findings on cardiovascular disease, skeletal tissues, and reproductive cancers are reviewed. Phyto-oestrogen concentrations in blood may be maintained at high levels in those consuming soyabean (Glycine max)-based food daily at several meals and exert their effects on target cells through either genomic effects via the classical oestrogen receptors or non-genomic effects mediated by membrane-bound oestrogen receptors or other cellular proteins. The expression of oestrogen receptor (OR) subtypes alpha (a) and beta (beta) varies across tissues, and cells that preferentially express OR-beta, which may include bone cells, are more likely to respond to phyto-oestrogens. Conversely, reproductive tissues contain relatively more OR-a and may, thus, be differently affected by phyto-oestrogens. Soyabean phyto-oestrogens appear to prevent the progression of atherosclerosis through multiple interactions, including lowering of plasma lipids and lipoproteins, increased vasodilatation and, possibly, decreased activation of blood platelets and vascular smooth muscle cells. However, a favourable impact on cardiovascular disease morbidity and mortality by a soyabean-enriched western-type diet remains to be shown, and unresolved questions remain regarding dose and form of the phyto-oestrogens in relation to risks and benefits. The isoflavones of soyabean have been shown consistently to have bone-retentive effects in animal studies by several investigators using rodent models, although intakes must be above a relatively high threshold level for a lengthy period of time, and little or no extra benefit is observed with intakes above this threshold level. The reports of modest or no effects on prevention of bone loss in human and non-human primate studies respectively, may be due to the limited doses tested so far. The relationship between soyabean-food intake and cancer risk has been more extensively investigated than for any other disease, but with less certainty about the benefits of long-term consumption of phyto-oestrogen-containing foods on prevention of cancer. The observations that breast and prostate cancer rates are lower in Asian countries, where soyabean foods are consumed at high levels, and the high isoflavone content of soyabeans have led to examination of the potential protective effects of phyto-oestrogens. Establishing diet-cancer relationships has proved difficult, in part because of the conflicting data from various studies of effects of soyabean-diets on cancer. Epidemiological evidence, though not impressive, does suggest that soyabean intake reduces breast cancer risk. The isoflavone genistein has a potent effect on breast cancer cells in vitro, and early exposure of animals to genistein has been effective in reducing later development of mammary cancer. Thus, continuous consumption of soyabean foods in early life and adulthood may help explain the low breast cancer mortality rates in Asian countries. Although the evidence for a protective effect against prostate cancer may be slightly more supportive, more research is needed before any firm conclusions can be made about the phyto-oestrogen-cancer linkages.

Analysis of estrogenic activity of foodstuffs and cigarette smoke condensates using a yeast estrogen screening method

Hormone mimics present in our environment are of concern because such agents could potentially reduce fertility and increase sexual dysfunction in wildlife and increase the risk of breast and reproductive organ cancers in man. Therefore, monitoring of the levels of estrogenic compounds in environmental materials is essential in order to prevent their exposure to man and to discover potential harmful effects on human health. In the present study, we analyzed estrogenic activity in 23 foodstuffs and cigarette smoke condensate samples extracted with an organic solvent, using the yeast estrogen screening (YES) system. Three soybean-related foodstuffs (soy sauce, tofu, miso), beer, coffee and cigarette smoke condensates showed clear estrogenic activity in the YES system. HPLC fractionations followed by the YES of these YES-positive samples revealed the presence of many estrogenic compounds in cigarette smoke condensates, whereas the other samples exerted estrogenic activities in only one or two fractions. Genistein was able to be isolated as the major active principle in soy sauce, tofu and miso, its concentration in these three foodstuffs ranging from 0.1 to 394 microg/g or ml. 8-Prenylnaringenin was also isolated from beer extracts as a major compound with estrogenic activity present at 0.22-4.0 ng/ml. Estrogenic activity of 8-prenylnaringenin with YES was 10-times as high as that of genistein, although it was 100-times less than that of 17beta-estradiol. Based on our results in vitro, 10 mg miso and 10 ml beer can be calculated to have similar estrogenic activity to 1 pmole 17beta-estradiol. It is very important that the effects of genistein and 8-prenylnaringenin on human health are elucidated.

Steroid hormone mimics: molecular mechanisms of cell growth and apoptosis in normal and malignant mammary epithelial cells

Anti-estrogen (anti-E2) therapy with E2 receptor antagonists has a significant benefit in women with breast cancer, but it may also increase the risk for developing hormone-independent breast cancer for which there is no therapy similar to that used in hormone-dependent breast cancer. Therefore, there is a significant interest in the development of compounds that may provide therapeutic benefit for hormone-independent breast cancer without untoward risks and adverse effects. The estrogen receptor (ER) modulators with both agonistic as well as antagonistic properties may, thus, be exploited for the development of the next generation of compounds for the prevention and/or treatment of breast cancer. In this article, we have discussed the clinical indications, risks, benefits and mechanisms of action of ER modulators and related compounds, particularly indole-3-carbinol (I3C), which may open new avenues for the prevention and/or treatment of breast cancer.

Tectorigenin, an isoflavone of Pueraria thunbergiana Benth., induces differentiation and apoptosis in human promyelocytic leukemia HL-60 cells

Cytotoxic effects of six isoflavonoids, tectorigenin, glycitein, tectoridin, glycitin, 6''-O-xylosyltectoridin, and 6''-O-xylosylglycitin isolated from the flower of Pueraria thunbergiana Benth. together with genistein, a known differentiation and apoptosis inducer, were examined. Among these isoflavonoids, tectorigenin and genistein exhibited cytotoxicity against various human cancer cells; glycitein showed only mild cytotoxicity. These results suggest that the isoflavone structure and 5-hydroxyl group are crucial for the cytotoxic properties and that glycosides are inactive. Moreover, tectorigenin induced differentiation of human promyelocytic leukemia HL-60 cells to granulocytes and monocytes/macrophages, and caused apoptotic changes of DNA in the cells, as did genistein. Tectorigenin also inhibited autophosphorylation of epidermal growth factor (EGF) receptor by EGF and decreased the expression of Bcl-2 protein, with less activity than genistein. From these results, tectorigenin may be a possible therapeutic agent for leukemia.

Effect of plant flavonoids on immune and inflammatory cell function

The flavonoids are a large group of naturally occurring phenylchromones found in fruits, vegetables, grains, bark, roots, stems, flowers, tea, and wine. Up to several hundred milligrams are consumed daily in the average Western diet. Only limited information is available on the absorption, distribution, metabolism, and excretion of these compounds in man. Some compounds are absorbed, however, and measurable plasma concentrations are achieved which could have pharmacological relevance. A variety of in vitro and in vivo experiments have shown that selected flavonoids possess antiallergic, antiinflammatory, antiviral and antioxidant activities. Moreover, acting by several different mechanisms, particular flavonoids can exert significant anticancer activity including anticarcinogenic properties and even a prodifferentiative activity, amongst other modes of action. Certain flavonoids possess potent inhibitory activity against a wide array of enzymes, but of particular note is their inhibitory effects on several enzyme systems intimately connected to cell activation processes such as protein kinase C, protein tyrosine kinases, phospholipase A2, and others. Evidence suggests that only activated cells are susceptible to the modulating effects of flavonoids, i.e. cells which are responding to a stimulus. The stimulated activities of numerous cell types, including mast cells, basophils, neutrophils, eosinophils, T & B lymphocytes, macrophages, platelets, smooth muscle, hepatocytes, and others, can be influenced by particular flavonoids. On balance, a considerable body of evidence suggests that plant flavonoids may be health-promoting, disease-preventing dietary compounds.

Reactions of Genistein with alkylperoxyl radicals

Antioxidant actions of the soy isoflavone genistein are believed to contribute to its overall chemopreventive activity. However, the mechanisms of its antioxidant reactions remain unknown. The objective of this study was to characterize the reaction products of genistein (5,7,4'-trihydroxyisoflavone) with peroxyl radicals generated by thermolysis of 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). Genistein oxidations with AMVN-derived peroxyl radicals yielded orobol (5,7,3',4'-tetrahydroxyisoflavone), a hydroxylated derivative of genistein, and several stable adducts of 4'-oxogenistein with AMVN-derived radicals. Some of these adducts include novel structures resulting from secondary oxidations of the AMVN-derived moiety. For all the observed oxidation products, the modifications occurred on the B-ring of the molecule. Genistein oxidation product structures provide potentially useful markers of genistein antioxidant chemistry.

Soyfoods, soybean isoflavones, and bone health: a brief overview

Soyfoods have received considerable attention during the past 5 years for their role in disease prevention, especially in relation to heart disease, osteoporosis, and cancer. However, limited research also suggests that soy protein favorably affects renal function. Much of the research interest in soy is aimed at establishing the physiological effects of isoflavones. Isoflavones are diphenolic compounds that have a very limited distribution in nature. Soybeans and soyfoods are, for practical purposes, the only nutritionally relevant dietary sources of isoflavones. Isoflavones are weak estrogens in that they bind to estrogen receptors, but they also have important nonhormonal properties as well. Initial speculation that soyfoods, and in particular isoflavones, might promote bone health was based on the estrogenic properties of isoflavones and the similarity in structure between isoflavones and the osteoporosis drug, ipriflavone, which is a synthetic isoflavone. In ovariectomized rodents, isoflavones retard bone loss almost as effectively as estrogen. Most research, but not all, also indicates that soyfoods rich in isoflavones favorably affect bone turnover and spinal bone mineral density in perimenopausal and postmenopausal women. However, studies conducted thus far have been of short duration and involved small numbers of subjects. Furthermore, no studies have actually examined the effect of soy feeding on fracture risk. Thus, although the data in general are encouraging, no firm conclusions can be drawn about the relationship between soy consumption and bone health. In addition to a possible direct effect of isoflavones on bone tissue, soy protein when substituted for animal protein may indirectly enhance bone strength. Several studies have found that in comparison with animal protein, soy protein decreases calcium excretion, a result of the lower sulfur amino acid content of soy protein. Although the high potassium content of soy is a consideration, the evidence clearly indicates that clinicians should consider recommending that their renal patients incorporate soyfoods into their diet.

Metabolism of genistein by rat and human cytochrome P450s

The metabolism of genistein (4',5,7-trihydroxyisoflavone), a phytoestrogen derived from soy products, was investigated using rat and human liver microsomes and recombinant human cytochrome P450 enzymes. Metabolism of genistein by microsomes obtained from rats treated with pyridine, phenobarbital, beta-naphthoflavone, isosafrole, pregnenolone-16alpha-carbonitrile, or 3-methylcholanthrene resulted in very different product profiles consisting of five different NADPH- and time-dependent metabolites as observed by HPLC reverse-phase analysis at 260 nm. The metabolism of genistein was also investigated with recombinant human cytochrome P450 1A1, 1A2, 1B1, 2B6, 2C8, 2E1, or 3A4. P450s 1A1, 1A2, 1B1, and 2E1 metabolized genistein to form predominantly one product (peak 3) with smaller amounts of peaks 1 and 2. P450 3A4 produced two different products (peaks 4 and 5). Product peaks 1-3 eluted off the HPLC column prior to the parent compound genistein, and the UV/vis spectra, GC/MS, and ESI/MS/MS analyses support the conclusion that these products result from hydroxylation of genistein. The product peak 3 has been identified by tandem mass spectrometry as 3',4',5, 7-tetrahydroxyisoflavone, also known as orobol, and peaks 1 and 2 appear to be hydroxylated at position 6 or 8.

Nutrition and prostate cancer

Scientific evidence suggests that differences in the diet may, in large part, account for the variability of prostate cancer rates around the world. Epidemiologic studies and animal experiments have yielded compelling results to warrant clinical intervention studies on nutrition from scientists who work on the prevention and treatment of prostate cancer. This article reviews the most recent evidence as to possible mechanisms of action of various dietary constituents, and explores evidence of various nutritional strategies for the prevention of prostate cancer progression.

Soyfoods, isoflavones and risk of colonic cancer: a review of the in vitro and in vivo data

Soy foods and soybean components have received considerable attention of late for their potential role in reducing cancer risk. Although the relationship between soy intake and the risk of breast and prostate cancer has been the focus of most interest, the relationship between soy intake and other cancers, including colorectal cancer, has also been studied. Several anti-carcinogens have been identified in soybeans, but most enthusiasm for the potential anti-cancer effects of soy undoubtedly stems from work involving soybean isoflavones. Isoflavones have a limited distribution in nature, and, for practical purposes, soyfoods are the only nutritionally relevant dietary source of these phytochemicals. Isoflavones are weak oestrogens but possess other potentially important biological attributes independent of their ability to bind to the oestrogen receptor. The isoflavone genistein inhibits the growth of most types of hormone-dependent and hormone-independent cancer cells in vitro, including colonic cancer cells. Several mechanisms for the in vitro anti-cancer effects of genistein have been proposed, including effects on signal transduction. A number of epidemiological studies, primarily of Asian origin, have examined the relationship between soy intake and the risk of colorectal cancer. Although these studies provide little support for a protective effect of soy, concerns have been raised about the completeness of the soy intake data, since soy was not the focus of these studies and most of this research was conducted prior to the recent interest in the anti-cancer effects of soy. The effect of soy/isoflavone intake has also been studied in rodents, but again these data are conflicting and provide only modest support for a protective effect. Although the relationship between soy intake and colonic cancer risk is certainly worthy of further investigation, there is, at the moment, very limited support for soy exerting a protective effect against this type of cancer.

Human immunodeficiency virus type 1 induction mediated by genistein is linked to cell cycle arrest in G2

Protein tyrosine kinase (PTK) phosphorylation is involved in cellular proliferation and differentiation processes that are key factors for human immunodeficiency virus type 1 (HIV-1) regulation in infected monocytic cells. Short-term exposure of the chronically infected promyelocytic OM10 cell line with the PTK inhibitor genistein induced a dose-dependent increase in p24 antigen production in culture supernatants. This induction persisted in the presence of the reverse transcriptase inhibitor, zidovudine, and was associated with an increased transcription of HIV-1 multiply spliced and unspliced RNAs, suggesting a transcriptional mechanism targeting the integrated provirus. Genistein induced cell differentiation, apoptosis, and a G2 arrest in the OM10 cells. Cell differentiation and apoptosis were not directly involved in the observed increase in HIV-1 replication that was closely linked to genistein-induced G2 arrest. Alleviation of the G2 arrest by pentoxyfylline resulted in a concomitant reduction of HIV-1 to baseline replication. Additionally, by flow cytometry, a significant increase in the number of p24 antigen-expressing cells was observed in cells arrested in G2 compared to those located in G1 or S. Tyrosine kinase inhibition was found not to be essential for enhanced viral replication, which seemed to be related to two other properties of genistein, inhibition of topoisomerase II activity and inhibition of phosphotidylinositol turnover. These findings are consistent with the recent observation that HIV-1 Vpr induces viral replication through preventing proliferation of cells by arresting them in G2 of the cell cycle and strongly suggest that manipulation of the cell cycle plays an important role in HIV-1 pathogenesis.

Involvement of SA channels in orienting response of cultured endothelial cells to cyclic stretch

The present work was designed to elucidate the involvement of Ca(2+)-permeable stretch-activated (SA) channels in the orienting response of endothelial cells to uniaxial cyclic stretch. Endothelial cells from human umbilical vein were cultured on an elastic silicone membrane and subjected to uniaxial cyclic stretch (120% in length, 1 Hz). The cells started to change their morphology 15 min after the onset of stretch, and > 90% of the cells oriented perpendicularly to the stretch axis after 2 h. Associated with the orienting response, cell elongation proceeded with a slower rate. Both of the orientating and elongating responses were largely inhibited by the removal of external Ca2+ or by Gd3+, a potent blocker for the SA channel, but not by nifedipine. Intracellular Ca2+ concentration ([Ca2+]i) transiently increased in response to uniaxial stretch, and the basal [Ca2+]i gradually increased during cyclic stretch. This Ca2+ response was inhibited by the removal of extracellular Ca2+ or by the addition of Gd3+. These results suggest that stretch-dependent Ca2+ influx through SA channels is essential in the stretch-dependent cell orientation and elongation.

Tumour necrosis factor-alpha-induced ICAM-1 expression in human vascular endothelial and lung epithelial cells: modulation by tyrosine kinase inhibitors

1. Tumour necrosis factor-alpha (TNF alpha) increases the expression of the adhesion molecule intercellular adhesion molecule-1 (ICAM-1) on cultured endothelial and epithelial cells and modulation of this may be important in controlling inflammation. Activation of tyrosine kinase(s) is known to be involved in the signal transduction pathways of many cytokines. In this study we have investigated the effects of the tyrosine kinase inhibitors, ST638, tyrphostin AG 1288 and genistein, on TNF alpha-induced ICAM-1 expression in human alveolar epithelial (A549) and vascular endothelial (EAhy926) cell lines and also normal human lung microvascular endothelial cells (HLMVEC). 2. ICAM-1 expression on cultured cells was determined by a sensitive enzyme-linked immunosorbant assay (ELISA). Endothelial or epithelial monolayers were exposed to increasing doses of TNF-alpha (0.01-10 ng ml-1), in the presence or absence of either ST638 (3-100 microM), AG 1288 (3-100 microM) or genistein (100 microM) and ICAM-1 expression was measured at 4 and 24 h. Control experiments examined the effect of ST638 on phorbol 12-myristate 13-acetate (PMA, 20 ng ml-1, 4 h)-stimulated ICAM-1 and compared it to that of a specific protein kinase C inhibitor, R031-8220 (10 microM). Also, functional consequences of changes in ICAM-1 expression were assessed by measuring adhesion of 111 In-labelled human neutrophils to EAhy926 endothelial and A549 epithelial monolayers treated with TNF alpha, in the presence or absence of ST638. 3. ST638 caused a concentration-dependent reduction in TNF alpha- (0.1-10 ng ml-1)-induced ICAM-1 on EAhy926 endothelial (at 4 h) and A549 epithelial monolayers (at 4 and 24 h). In contrast, ST638 caused a concentration-dependent increase in TNF alpha- (0.1-10 ng ml-1)-induced ICAM-1 on EAhy926 endothelial cells at 24 h. Similar effects were seen with AG 1288 or genistein. ST638 (100 microM) significantly (P < 0.01) inhibited ICAM-1 expression on HLMVEC endothelial cells induced by 0.01 ng ml-1 TNF alpha at 4 or 24 h or 0.1 ng ml-1 at 4 h, but increased ICAM-1 expression induced by 0.1 ng ml-1 TNF alpha at 24 h. ST638 did not significantly change the expression of PMA-stimulated ICAM-1 on either A549 epithelial, EAhy926 or HLMVEC endothelial cells. However, PMA-induced ICAM-1 expression was inhibited by Ro31-8220. Also, treatment of epithelial or endothelial monolayers with TNF alpha and ST638 altered adhesion of human neutrophils to A549 epithelial or EAhy926 endothelial cells in a manner that corresponded to the alteration in ICAM-1 expression. 4. These results show that tyrosine kinase inhibitors alter TNF alpha-induced ICAM-1 expression, but that the cell type, concentration of TNF alpha and time of exposure to this cytokine determine whether expression is decreased or increased by the inhibitor. An increased understanding of the signal transduction pathway(s) involved in TNF alpha-induced ICAM-1 expression on lung epithelial and vascular endothelial cells may be of potential therapeutic value in the treatment of inflammatory disease.

High-performance liquid chromatographic assay for genistein in biological fluids

A specific, sensitive and technically convenient HPLC method for assaying genistein in biological fluids has been developed. The compound and 4-hydroxybenzophenone, added as an internal standard, were efficiently isolated from both plasma and urine by extraction with tert-butyl methyl ether. Following evaporation of the organic solvent, the extract was reconstituted with methanol-0.05 M ammonium acetate buffer, pH 4.7 (30:70, v/v), and loaded onto a 4 microns Nova-Pak C8 column (15 cm x 3.9 mm I.D.). Chromatography was performed at ambient temperature using a mobile phase of acetonitrile-0.05 M ammonium formate buffer, pH 4.0 (27:73, v/v), at a flow-rate of 1.0 ml/min, with UV detection at 260 nm. Mean values of the tR for the drug and internal standard, determined from chromatograms of the 1 microgram/ml plasma standard during a 6 month period, were 8.27 +/- 0.55 and 11.92 +/- 0.71 min, respectively (S.D., n = 29). With a sample volume of 50 microliters, the lowest concentration of genistein included in the plasma standard curve, 0.020 microgram/ml, was quantified with a 10.7% R.S.D. over a 5 month period. Plasma standards having concentrations of 0.050 to 1.02 micrograms/ml exhibited R.S.D. values ranging from 2.3 to 6.1%. The drug was quantified in urine with similar reproducibility. The sensitivity of the assay was adequate for characterizing the plasma pharmacokinetics of genistein in the mouse and dog. However, a 10-fold improvement in sensitivity was afforded by increasing the sample size to 250 microliters, without otherwise modifying the method. Thus, this procedure may prove suitable for determining plasma and urine levels of genistein in humans consuming dietary isoflavonoids in a much more convenient manner than permitted by existing methodology.

Genistein augments cyclic adenosine 3'5'-monophosphate(cAMP) accumulation and insulin release in MIN6 cells

Effects of genistein on insulin release were studied using MIN6 cells, a glucose-sensitive insulinoma cell line. At the non-stimulatory concentrations of glucose, genistein did not affect insulin release, however, at the stimulatory concentrations of glucose, genistein significantly increased insulin release in a dose-dependent manner up to 20 micrograms/ml. The content of cAMP in MIN6 cells was also elevated significantly by genistein and the dose-response relationship between the genistein and cAMP accumulation was consistent with the relationship between the genistein and insulin release. These effects were inhibited by calcium antagonists or by the omission of extracellular calcium. Isobutylmethylxanthine (IBMX;0.1mM) increased both cAMP accumulation and insulin release in MIN6 cells and there were no additive effects by the addition of genistein. The accumulation of cAMP might have, at least in part, resulted from phosphodiesterase inhibition by genistein. These results suggest that genistein augments glucose-induced insulin release by the contribution of cAMP accumulation and calcium modulation which depends on extracellular calcium.

ED-110, a novel indolocarbazole, prevents the growth of experimental tumors in mice

A new indolocarbazole compound, ED-110, which was obtained by glucosylating a microbial product (BE-13793C) and is a potent topoisomerase I inhibitor, showed characteristic inhibitory effects on the growth of 12 human tumor cell lines tested. The IC50 values of ED-110 against 9 of the 12 lines ranged from 11.5 micrograms/ml to 0.07 microgram/ml, while the remaining 3 lines were quite resistant (IC50, > 100 micrograms/ml). In in vivo experiments, i.p. treatment with ED-110 increased the survival period by more than two-fold in mice implanted i.p. with P388, L1210, L5178Y or EL4 murine leukemic cells. The minimum effective dose increasing the life-span of mice bearing P388 leukemia by 25% was < 2.5 mg/kg/day x 10 and the maximum tolerated dose was > 160 mg/kg/day x 10. ED-110 was also effective against the spontaneous metastasis of mouse Meth A fibrosarcoma cells and the growth of xenografted MKN-45 human stomach cancer cells as well as s.c. implanted mouse colon 26 and IMC carcinoma cells. These results indicated that ED-110 may have potential as a new antineoplastic agent with a large chemotherapeutic index and a wide range of effective doses.

Differentiation of human monoblastic leukemia U937 cells induced by inhibitors of myosin light chain kinase and prevention of differentiation by granulocyte-macrophage colony-stimulating factor

Inhibitors of protein kinase activities are useful for the study of intracellular signal transduction and some of these inhibitors are reported to induce differentiation of human leukemia cells. We examined effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) in combination with several kinase inhibitors on differentiation of human leukemia U937 cells. Nitroblue tetrazolium (NBT)-reducing activity, a typical marker of myelomonocytic differentiation, of U937 cells was induced by genistein and GM-CSF enhanced this activity. GM-CSF also induced the NBT-reducing activity of the cells in combination with 2,5-dihydroxycinnamic acid methyl ester, psi-tectorigenin and staurosporine, although each of them did not induce the activity. Inhibitors of myosin light chain kinase, 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-9) and 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7), induced in U937 cells NBT-reduction, and lysozyme and alpha-naphthyl acetate esterase activities. GM-CSF inhibited this differentiation and counteracted the anti-proliferation effect of the kinase inhibitors. These results suggest that some protein kinases are involved in differentiation of U937 cells and the kinases inhibited by ML-9 and ML-7 are associated with signal transduction of GM-CSF.

Genistein and biochanin A inhibit the growth of human prostate cancer cells but not epidermal growth factor receptor tyrosine autophosphorylation

The effect of the isoflavones, genistein, daidzein, and biochanin A on the growth of the LNCaP and DU-145 human prostate cancer cell lines has been examined. Genistein and biochanin A, but not daidzein, inhibit both serum and EGF-stimulated growth of LNCaP and DU-145 cells (IC50 values from 8.0 to 27 micrograms/ml for serum and 4.3 to 15 micrograms/ml for EGF), but have no significant effect of the EGF receptor tyrosine autophosphorylation. In contrast, tyrphostin 25, a specific EGF receptor tyrosine kinase inhibitor, inhibits EGF-stimulated growth and EGF receptor tyrosine autophosphorylation in these whole cells, but does not inhibit serum-stimulated growth. These data suggest that the mechanism of action of genistein and biochanin A does not depend on inhibition of EGF receptor tyrosine autophosphorylation, but on a more distal event in the EGF receptor-mediated signal transduction cascade.

Ipriflavone inhibits phosphoinositide hydrolysis and Ca2+ uptake in the osteoblast-like UMR-106 cells

The mechanism of action of ipriflavone, an isoflavone derivative, was studied in the osteoblastic-like UMR-106 cell line. Ipriflavone affected both phosphoinositide hydrolysis and 45Ca2+ uptake. A repeated treatment of UMR-106 cells (once a day, for 3 days) with ipriflavone decreased, in a concentration-dependent manner, [3H]inositol monophosphate accumulation. This effect was also achieved after single addition of high concentrations of ipriflavone or 100 nM [Asu1,7]eel-calcitonin, a semi-synthetic analog of eel calcitonin. When repeatedly added to UMR-106 cells, 17 beta-estradiol produced a marked inhibition of [3H]inositol monophosphate accumulation, an effect which appeared significant only at a concentration of 1 microM and which was accompanied by a reduced incorporation of [3H]inositol into membrane phospholipids. A repeated treatment with ipriflavone reduced 45Ca2+ uptake as well. This effect was observed also after a single addition of [Asu1,7]eel-calcitonin but not following single or repeated treatment with 17 beta-estradiol. The present data indicate the osteoblast as a direct and specific target for ipriflavone and suggest that this compound may share intracellular transducing mechanisms with other antiosteoporotic hormones such as estrogen and calcitonin.

Effects of flavonoids on immune and inflammatory cell functions

No doubt can remain that the flavonoids have profound effects on the function of immune and inflammatory cells as determined by a large number and variety of in vitro and some in vivo observations. That these ubiquitous dietary chemicals may have significant in vivo effects on homeostasis within the immune system and on the behavior of secondary cell systems comprising the inflammatory response seems highly likely but more work is required to strengthen this hypothesis. Ample evidence indicates that selected flavonoids, depending on structure, can affect (usually inhibit) secretory processes, mitogenesis, and cell-cell interactions including possible effects on adhesion molecule expression and function. The possible action of flavonoids on the function of cytoskeletal elements is suggested by their effects on secretory processes. Moreover, evidence indicates that certain flavonoids may affect gene expression and the elaboration and effects of cytokines and cytokine receptors. How all of these effects are mediated is not yet clear but one important mechanism may be the capacity of flavonoids to stimulate or inhibit protein phosphorylation and thereby regulate cell function. Perhaps the counterbalancing effect of cellular protein tyrosine phosphatases will also be found to be affected by flavonoids. Some flavonoid effects can certainly be attributed to their recognized antioxidant and radical scavenging properties. A potential mechanism of action that requires scrutiny, particularly in relation to enzyme inhibition, is the redox activity of appropriately configured flavonoids. Finally, in a number of cell systems it seems that resting cells are not affected significantly by flavonoids but once a cell becomes activated by a physiological stimulus a flavonoid-sensitive substance is generated and interaction of flavonoids with that substance dramatically alters the outcome of the activation process.

Isoflavonoids, genistein, psi-tectorigenin, and orobol, increase cytoplasmic free calcium in isolated rat hepatocytes

Isoflavonoid compounds, genistein, psi-tectorigenin and orobol have been implicated as inhibitors of tyrosine-specific protein kinase and phosphatidylinositol turnover. These compounds have been frequently used as a pharmacological tool to assess signal transduction pathways in various cell systems. In the course of analyzing signaling pathways in rat hepatocytes, we obtained an unexpected finding that these compounds transiently increase cytoplasmic free calcium. Since the Ca2+ mobilizing effect was observed in 1 microM calcium containing buffer, the source of the Ca2+ may be intracellular stores. Thus, when interpreting data obtained using these compounds, caution is needed.

Effects of ipriflavone and its metabolites on a clonal osteoblastic cell line

Protective effects of ipriflavone, an isoflavone derivative, in osteoporosis are believed to be caused by the inhibitory action on bone resorption. A direct effect of ipriflavone on bone formation is as yet unknown. Ipriflavone and four of its metabolites (I, II, III, and V) were examined for their effects on parathyroid hormone response, collagen synthesis, alkaline phosphatase activity, and cell proliferation in a clonal cell population of rat osteoblastic cells. Pretreatment of osteoblasts with high concentrations of ipriflavone for 48 h significantly inhibited the cAMP response to parathyroid hormone, producing a shift in the dose-response curve; at lower concentrations metabolites II and III potentiated the cAMP accumulation induced by low doses of parathyroid hormone. The 48 h treatment with metabolite V at the 1 nM dose significantly stimulated collagen synthesis in osteoblastic cells. Ipriflavone and metabolite I showed a biphasic stimulatory action on the alkaline phosphatase activity of osteoblasts, with a maximal effect at the 0.1 and 1 nM doses, respectively. A similar biphasic response was observed with ipriflavone and metabolite I on osteoblastic cell growth, with a maximal effect at the 0.1 nM concentration. These results suggest a direct role of ipriflavone in modulating the synthetic and growth properties of osteoblast-like cells.

Genistein inhibition of the growth of human breast cancer cells: independence from estrogen receptors and the multi-drug resistance gene

The effect of isoflavones on the growth of the human breast carcinoma cell lines, MDA-468 (estrogen receptor negative), and MCF-7 and MCF-7-D-40 (estrogen receptor positive), has been examined. Genistein is a potent inhibitor of the growth of each cell line (IC50 values from 6.5 to 12.0 micrograms/ml), whereas biochanin A and daidzein are weaker growth inhibitors (IC50 values from 20 to 34 micrograms/ml). The isoflavone beta-glucosides, genistin and daidzin, have little effect on growth (IC50 values greater than 100 micrograms/ml). The presence of the estrogen receptor is not required for the isoflavones to inhibit tumor cell growth (MDA-468 vs MCF-7 cells). In addition, the effects of genistein and biochanin A are not attenuated by overexpression of the multi-drug resistance gene product (MCF-7-D40 vs MCF-7 cells).

Effects of inhibitors of protein tyrosine kinase activity and/or phosphatidylinositol turnover on differentiation of some human myelomonocytic leukemia cells

The activities of protein tyrosine kinase and phosphatidylinositol turnover have been found to be associated with cell growth and differentiation. We examined the effects of some inhibitors for these biochemical activities in human myelogenous leukemia cells. Genistein, which is known to inhibit the activities of protein tyrosine kinase, phosphatidylinositol turnover and topoisomerase II, induced nitroblue tetrazolium (NBT) reduction and lysozyme activity in ML-1, HL-60 and U937 cells. Morphological studies showed that genistein-induced differentiation of myeloblastic ML-1 cells into promyelocytes and of promyelocytic HL-60 cells into mature granulocytes. The differentiation-inducing effect of genistein was augmented by addition of 1 alpha,25-dihydroxyvitamin D3 (VD3) or retinoic acid, VD3 being more effective than retinoic acid. Methyl 2,5-dihydroxycinamate, a protein tyrosine kinase inhibitor, had only a weak effect in inducing differentiation of ML-1 cells. On the other hand, psi-tectorigenin was more effective than genistein in inducing the differentiations of ML-1 and HL-60 cells. Psi-tectorigenin is reported to inhibit phosphatidylinositol turnover without inhibiting protein tyrosine kinase. Thus modulation of phosphatidylinositol turnover might be more important than that of protein tyrosine kinase activity for differentiation of some myelogenous leukemia cells.

Exogenous gangliosides stimulate breakdown of neuro-2A phosphoinositides in a manner unrelated to neurite outgrowth

Gangliosides administered exogenously are well-known effectors of differentiation in many neuroblastoma lines and primary neuronal cultures. Previous studies suggested the phosphoinositide signaling mechanism could be a contributing factor. We have found that treatment of Neuro-2A cells with bovine brain ganglioside mixture (BBG) causes breakdown of phosphoinositides, as measured by increased levels of inositol phosphates. The effect was optimal at 60 min and required a minimal BBG concentration of 25 microM. However, addition of neomycin, which blocked phosphoinositide breakdown, had no observable effect on ganglioside-stimulated neurite outgrowth. A similar result was obtained with psi-tectorigenin, which also inhibited phosphoinositide hydrolysis. When cells were treated with maitotoxin, an agent that promotes phosphoinositide breakdown, there was no enhancement of neurite outgrowth. These findings indicate that although exogenous gangliosides elevate inositol phosphate formation over a prolonged period in neuro-2A cells, this reaction is not integral to the differentiation of these cells. The possibility of secondary effects influencing neurite type and structure cannot be excluded.