Bioavailability of soybean isoflavones depends upon gut microflora in women.

J Nutr, 125(9):2307-15 1995 Sep

Soybean isoflavones have been proposed to be anticarcinogenic, but their effective doses have not been established. To study their bioavailability, seven women consumed 3.4, 6.9, or 10.3 mumol isoflavones/kg body wt in soymilk in each of three meals of a liquid diet on one of three feeding days that were separated by 2-wk washout periods. Subjects were randomly assigned to doses in a cross-over design. Plasma, urine and fecal isoflavones were measured by reverse phase HPLC. In two subjects, fecal isoflavone recovery was 10-20 times that in the other five subjects. Average 48-h urinary recoveries of ingested daidzein and genistein were 16 +/- 4 and 10 +/- 4%, respectively, at all three doses among the five subjects excreting only small amounts of isoflavones in feces, whereas urinary recoveries of daidzein and genistein in the two subjects who excreted large amounts of fecal isoflavones were 32 +/- 5 and 37 +/- 6%, respectively. Urinary isoflavone excretion was nearly zero in all subjects at 48 h after dosing. Average plasma concentration of genistein at 24 h after the breakfast isoflavone dose in subjects excreting large amounts of fecal isoflavones was significantly greater by 2.5-fold than in subjects who excreted small amounts of fecal isoflavones (P < 0.05). In vitro anaerobic incubation of isoflavones with human feces showed that intestinal half-life of daidzein and genistein may be as little as 7.5 and 3.3 h, respectively. These data suggest that human isoflavone bioavailability depends upon the relative ability of gut microflora to degrade these compounds.




Rationale for the use of genistein-containing soy matrices in chemoprevention trials for breast and prostate cancer.

J Cell Biochem Suppl, 27(1):181-7 1995

Pharmacologists have realized that tyrosine kinase inhibitors (TKI) have potential as anti-cancer agents, both in prevention and therapy protocols. Nonetheless, concern about the risk of toxicity caused by synthetic TKIs restricted their development as chemoprevention agents. However, a naturally occurring TKI (the isoflavone genistein) in soy was discovered in 1987. The concentration of genistein in most soy food materials ranges from 1-2 mg/g. Oriental populations, who have low rates of breast and prostate cancer, consume 20-80 mg of genistein/day, almost entirely derived from soy, whereas the dietary intake of genistein in the US is only 1-3 mg/day. Chronic use of genistein as a chemopreventive agent has an advantage over synthetic TKIs because it is naturally found in soy foods. It could be delivered either in a purified state as a pill (to high-risk, motivated patient groups), or in the form of soy foods or soy-containing foods. Delivery of genistein in soy foods is more economically viable ($1.50 for a daily dose of 50 mg) than purified material ($5/day) and would require no prior approval by the FDA. Accordingly, investigators at several different sites have begun or are planning chemoprevention trials using a soy beverage product based on SUPRO, an isolated soy protein manufactured by Protein Technologies International of St. Louis, MO. These investigators are examining the effect of the soy beverage on surrogate intermediate endpoint biomarkers (SIEBs) in patients at risk for breast and colon cancer, defining potential SIEBs in patients at risk for prostate cancer, and determining whether the soy beverage reduces the incidence of cancer recurrence.




Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP.

Jpn J Clin Oncol, 208(1):360-3 1998 Jun

BACKGROUND: Epidemiological studies have suggested that soybean isoflavones are associated with a lower risk of prostate cancer. However, the mechanisms of prostate cancer prevention by soybean isoflavones have yet to be fully clarified. METHODS: Two soybean isoflavones (genistein and daidzein) and their glucosides (genistin and daidzin) were tested for their effects on cell growth and apoptosis of the LNCaP human prostatic cancer cell line. RESULTS: Among these isoflavones, genistein was found to inhibit the growth of LNCaP most effectively, with an IC50 value of 40 microM. The inhibition of cell growth by genistein was accompanied by the suppression of DNA synthesis and the induction of apoptosis. Expression of prostate-specific antigen (PSA) in LNCaP was also significantly reduced by the treatment with genistein. CONCLUSIONS: The results suggest that genistein might primarily influence human prostate cancer development by reducing tumor growth.




In vitro hormonal effects of soybean isoflavones.

J Nutr, 208(1):751S-756S 1995 Mar

Isoflavones exhibit a multitude of biological effects that influence cell growth and regulation, and, thus, may have potential value in the prevention and treatment of cancer. Isoflavones are weak estrogens and can function both as estrogen agonists and antagonists depending on the hormonal milieu and the target tissue and species under investigation. Genistein, one of the two primary isoflavones in soybeans, has attracted much attention from the research community, not only because of its potential antiestrogenic effects, but because it inhibits several key enzymes thought to be involved in carcinogenesis. Although still speculative, greater dietary incorporation of soybean products, because of the high concentration of isoflavones, may be a safe and effective means of reducing cancer risk.




Evolution of the health benefits of soy isoflavones.

Proc Soc Exp Biol Med, 208(1):386-92 1998 Mar

Soy is a unique dietary source of the isoflavones, genistein and daidzein. It has been part of the Southeast Asian diet for nearly five millenia, whereas consumption of soy in the United States and Western Europe has been limited to the 20th century. Heavy consumption of soy in Southeast Asian populations is associated with reduction in the rates of certain cancers and cardiovascular disease. Recent experimental evidence suggests that phytochemicals in soy are responsible for its beneficial effects, which may also include prevention of osteoporosis, a hereditary chronic nose bleed syndrome, and autoimmune diseases. Exposure of soy formula-fed infants to the potential estrogenizing effects of the isoflavones is limited by the first pass effect of the liver following the uptake of isoflavones from the gut. Several mechanisms of action of isoflavones have been proposed-both through estrogen-dependent and estrogen-independent pathways.




Antioxidant and antipromotional effects of the soybean isoflavone genistein.

Proc Soc Exp Biol Med, 208(1):124-30 1995 Jan

Antioxidant and antipromotional effects of the soybean isoflavone genistein have been studied in HL-60 cells and the mouse skin tumorigenesis model. Effects of structure-related flavone/isoflavones on hydrogen peroxide (H2O2) production by 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated HL-60 cells and superoxide anion (O2-) generation by xanthine/xanthine oxidase were compared. Of tested isoflavones, genistein is the most potent inhibitor among TPA-induced H2O2 formation by (dimethyl sulfoxide) DMSO-differentiated HL-60 cells, daidzein is second, and apigenin and biochanin A show little effect. In contrast, genistein, apigenin, and prunectin are equally potent in inhibiting O2- generation by xanthine/xanthine oxidase, with daidzein showing a moderate inhibitory effect and biochanin A exhibiting no effect. These results suggest that the antioxidant properties of isoflavones are structurally related and the hydroxy group at Position 4' is crucial in both systems. Dietary administration of 250 ppm genistein for 30 days significantly enhances the activities of antioxidant enzymes in the skin and small intestine of mice. Further studies show that genistein significantly inhibits TPA-induced proto-oncogene expression (c-fos) in mouse skin in a dose-dependent manner. In a two-stage skin carcinogenesis study, low levels of genistein (1 and 5 mumol) significantly prolong tumor latency and decrease tumor multiplicity by approximately 50%. We conclude that genistein's antioxidant properties and antiproliferative effects may be responsible for its anticarcinogenic effect. Its high content in soybeans and relatively high bioavailability favor genistein as a promising candidate for the prevention of human cancers.




Soy isoflavones improve systemic arterial compliance but not plasma lipids in menopausal and perimenopausal women.

Arterioscler Thromb Vasc Biol, 208(1):3392-8 1997 Dec

The possibility that the heightened cardiovascular risk associated with the menopause, which is said to be ameliorated by soybeans, can be reduced with soy isoflavones was tested in 21 women. Although several were perimenopausal, all have been included. A placebo-controlled crossover trial tested the effects of 80-mg daily isoflavones (45 mg genistein) over 5- to 10-week periods. Systemic arterial compliance (arterial elasticity), which declined with age in this group, improved 26% (P < .001) compared with placebo. Arterial pressure and plasma lipids were unaffected. The vasodilatory capacity of the microcirculation was measured in nine women; high acetylcholine-mediated dilation in the forearm vasculature was similar with active and placebo treatments. LDL oxidizability measured in vitro was unchanged. Thus, one important measure of arterial health, systemic arterial compliance, was significantly improved in perimenopausal and menopausal women taking soy isoflavones to about the same extent as is achieved with conventional hormone replacement therapy.




Synergistic action of quercetin and genistein in human ovarian carcinoma cells.

Oncol Res, 27(1):597-602 1997

Ovarian carcinoma is the fourth most common cause of cancer death in women and there has been a steady increase in the age-adjusted cancer death rates in the past 25 years in the US. However, patients who become cisplatin resistant respond poorly to available cytotoxic agents; therefore, discovering novel targets for ovarian carcinoma is vital. Quercetin, an anticancer agent, arrests the cell cycle at G1 and S phase boundary. Genistein, a plant flavonoid, attacks the cell cycle at G2 and/or early M phases in most carcinoma cells. Quercetin and genistein block the phosphatidylinositol conversion to IP3 signal transduction pathway mainly by inhibiting 1-phosphatidylinositol 4-kinase (PI kinase, EC 2.7.1.67) and 1-phosphatidylinositol 4-phosphate 5-kinase (PIP kinase, EC 2.7.1.68), respectively. Because each drug attacks a different phase of the cell cycle and reduces IP3 concentration by attacking different signal transduction enzymes, we tested the hypothesis that the two drugs might be synergistic in human carcinoma cells. In human ovarian carcinoma OVCAR-5 cells in growth inhibition assay, the IC50S for quercetin and genistein were (mean +/- SE) 66 +/- 3.0 and 32 +/- 2.5 microM; in clonogenic assays they were 15 +/- 1.2 and 5 +/- 0.5 microM, respectively. When quercetin was added to the cultures of OVCAR-5 cells followed 8 h later by genistein, synergism was observed in growth inhibition and clonogenic assays. The synergistic action of quercetin and genistein may be of interest in clinical treatment of human ovarian carcinoma.




Effect of structurally related flavones/isoflavones on hydrogen peroxide production and oxidative DNA damage in phorbol ester-stimulated HL-60 cells.

Nutr Cancer, 208(1):77-82 1997

We have examined the antioxidant properties of structurally related flavones/isoflavones in 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated HL-60 cells. In the presence of 1.3% dimethyl sulfoxide in the medium for seven days, promyelocytic HL-60 cells were differentiated into neutrophil-like cells possessing phagocytic properties and the capacity to generate H2O2 on TPA stimulation. The effects of five selected flavones/isoflavones on the formation of H2O2 and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were examined in TPA-stimulated HL-60 cells. The results indicated that genistein was the most potent inhibitor of H2O2 production by TPA-stimulated HL-60 cells, followed by apigenin and daidzein, whereas prunectin and biochanin A exhibited no effect. This inhibitory effect correlates well with the scavenging capacity of H2O2 by these flavones/isoflavones in an in vitro system. The formation of 8-OHdG in cellular DNA of HL-60 cells was induced by TPA and further enhanced by the addition of FeCl2 to the medium. Most flavones/isoflavones significantly inhibited TPA + FeCl2-induced 8-OHdG formation in HL-60 cells, with genistein being the most potent quencher. The inhibition of H2O2 production and 8-OHdG formation by these structurally related flavones/isoflavones may contribute to their chemopreventive potentials against human cancers.




Genistein inhibits both estrogen and growth factor-stimulated proliferation of human breast cancer cells.

Cell Growth Differ, 27(1):1345-51 1996 Oct

Genistein is a naturally occurring dietary protein tyrosine kinase (PTK) inhibitor that is hypothesized to be responsible for the lower rate of breast cancer observed in Asian women consuming soy. Although genistein is a potent in vitro PTK inhibitor, its mechanism of action in vivo is not known. In vivo, breast cancer growth is regulated by estrogens and peptide growth factors, such as epidermal growth factor (EGF), the receptor of which has intrinsic PTK activity. Therefore, genistein may block mammary epithelial cell growth by interfering with signal transduction events stimulated by estradiol or growth factors. The effect of genistein, related isoflavones, and other tyrosine kinase inhibitors on fetal bovine serum-, estradiol-, and EGF-stimulated cell growth and signal transduction pathways was examined in five human breast cancer cell lines. Genistein inhibited the growth of these cells by each of the growth stimuli with IC50 values ranging from 2.6 to over 20 micrograms/ml. Growth inhibition by genistein was cytostatic and reversible at IC50 concentrations. Related isoflavones were less potent growth inhibitors than genistein, whereas the synthetic PTK inhibitor tyrphostin A25 was an equally potent growth inhibitor. The mechanism of genistein growth inhibition in human breast cancer cells did not depend on the presence of functional estrogen receptor signaling pathways or on inhibition of EGF-receptor PTK activity. Furthermore, genistein (< or = 20 micrograms/ml) did not decrease constitutive or EGF-induced tyrosine phosphorylation as determined by Western blotting with antiphosphotyrosine antibodies. These data suggest that although genistein inhibits the growth of breast cancer cells in culture, it does so without gross inhibition of PTK activity.




Estrogenic and antiproliferative properties of genistein and other flavonoids in human breast cancer cells in vitro.

Nutr Cancer, 27(1):31-40 1997

Experimental and epidemiologic studies support the view that soyfoods prevent cancer as well as diseases and symptoms associated with estrogen deficiency. Recent research suggests that the isoflavonoid genistein, a phytoestrogen found in abundance in soyfoods, may be one of the principal molecular components responsible for these health benefits. In this study we investigated the effects of a broad physiologically relevant concentration range of genistein on estrogen receptor (ER) binding, induction of the estrogen-regulated antigen pS2, and cell proliferation rate in ER(+) and ER(-) human breast cancer cells grown in vitro. Dose response to genistein was compared with that of estradiol, tamoxifen, and several other structurally similar iso- and bioflavonoids (e.g., equol, kaempferol, and quercetin). Our results revealed that genistein has potent estrogen agonist and cell growth-inhibitory actions over a physiologically achievable concentration range (10 nM-20 microM). Other flavonoids over the same concentration range were good estrogen agonists and poor cell growth inhibitors (equol) or poor estrogen agonists and potent growth inhibitors (kaempferol and quercetin). The growth-inhibitory actions of flavonoids were distinctly different from those of triphenyl antiestrogens like tamoxifen. In summary, our results reveal that genistein is unique among the flavonoids tested, in that it has potent estrogen agonist and cell growth-inhibitory actions over a physiologically relevant concentration range.




Estrogen and progestin bioactivity of foods, herbs, and spices.

Proc Soc Exp Biol Med, 217(3):369-78 1998 Mar

In this study we report on the content and bioactivity of plant (phyto) estrogens and progestins in various foods, herbs, and spices, before and after human consumption. Over 150 herbs traditionally used by herbalists for treating a variety of health problems were extracted and tested for their relative capacity to compete with estradiol and progesterone binding to intracellular receptors for progesterone (PR) and estradiol (ER) in intact human breast cancer cells. The six highest ER-binding herbs that are commonly consumed were soy, licorice, red clover, thyme, tumeric, hops, and verbena. The six highest PR-binding herbs and spices commonly consumed were oregano, verbena, tumeric, thyme, red clover and damiana. Some of the herbs and spices found to contain high phytoestrogens and phytoprogestins were further tested for bioactivity based on their ability to regulate cell growth rate in ER (+) and ER (-) breast cancer cell lines and to induce or inhibit the synthesis of alkaline phosphatase, an end product of progesterone action, in PR (+) cells. In general, we found that ER-binding herbal extracts were agonists, much like estradiol, whereas PR-binding extracts, were neutral or antagonists. The bioavailability of phytoestrogens and phytoprogestins in vivo were studied by quantitating the ER-binding and PR-binding capacity of saliva following consumption of soy milk, exogenous progesterone, medroxyprogesterone acetate, or wild mexican yam products containing diosgenin. Soy milk caused a dramatic increase in saliva ER-binding components without a concomitant rise in estradiol. Consumption of PR-binding herbs increased the progestin activity of saliva, but there were marked differences in bioactivity. In summary, we have demonstrated that many of the commonly consumed foods, herbs, and spices contain phytoestrogens and phytoprogestins that act as agonists and antagonists in vivo.




Genistein, a dietary ingested isoflavonoid, inhibits cell proliferation and in vitro angiogenesis.

J Nutr, 27(1):790S-797S 1995 Mar

Consumption of a plant-based diet can prevent the development and progression of chronic diseases that are associated with extensive neovascularization. To determine whether prevention might be associated with dietary derived angiogenesis inhibitors, we have fractionated urine of healthy human subjects consuming a plant-based diet and examined the fractions for their abilities to inhibit the proliferation of vascular endothelial cells. One of the most potent fractions contained several isoflavonoids, which we identified by gas chromatography-mass spectrometry and subsequently synthesized. Of all synthetic compounds, the isoflavonoid genistein was the most potent and inhibited endothelial cell proliferation and in vitro angiogenesis at half maximal concentrations of 5 and 150 mumol/L, respectively. Moreover, genistein inhibited the proliferation of various tumor cells. Genistein excretion in urine of subjects consuming a plant-based diet is in the micromolar range, which is 30-fold higher than that of subjects consuming a traditional Western diet. The high concentrations of genistein in urine of vegetarians and our present results suggest that genistein may contribute to the preventive effect of plant-based diet on chronic diseases, including solid tumors, by inhibiting neovascularization and tumor cell proliferation. Thus genistein may have important applications in the treatment of solid tumors and angiogenic diseases.




Natural and synthetic isoflavones in the prevention and treatment of chronic diseases.

Calcif Tissue Int, 208(1):S5-8 1997

The evidence that natural isoflavones protect against several chronic diseases is both observational and experimental. In humans, epidemiologic findings clearly show a higher incidence of some common types of cancer (i.e., breast, prostate, and colon) and of coronary heart diseases in Western populations exposed to limited amounts of soybean isoflavones (i.e., genistein, daidzein) in the diet. Further evidence for cancer and cardiac protection and antiatherogenic effects resulting from soybean isoflavones administration has been noted in various experimental animal models. Isoflavones may also prevent postmenopausal bone loss and osteoporosis. In fact, genistein has been reported to be as active as estrogens in maintaining bone mass in ovariectomized rats. Moreover, the synthetic isoflavone derivative ipriflavone is able to reduce bone loss in various types of animal models of experimental osteoporosis providing a rationale on its use in the prevention and treatment of postmenopausal and senile osteoporosis in humans. The mechanism through which isoflavones may exert the above-mentioned effects seems to depend, at least in part, on their mixed estrogen agonist-antagonist properties. An alternative hypothetical mechanism could derive from other biochemical actions of isoflavones such as inhibition of enzymatic activity, in particular protein kinases, or activation of an "orphan" receptor distinct from the estrogen type I receptor.




A comparative survey of leguminous plants as sources of the isoflavones, genistein and daidzein: implications for human nutrition and health.

J Altern Complement Med, 208(1):7-12 1997 Spring

Over 80 taxa of mostly agriculturally important legumes were surveyed as sources of the metabolites, genistein and daidzein. Remarkably high concentrations (over 2 g.kg-1 dry weight) of the anticancer metabolite, genistein, were found in the leaves of Psoralea corylifolia (Indian bread root). All other legumes, with the exception of fermented soybean miso, had genistein levels < 400 mg.kg-1 dry weight. Concentrations of over 1 g.kg-1 dry weight and 0.95 g.kg-1 dry weight of the anticancer metabolite, daidzein, were found in the stems of the fava bean (Vicia faba) and roots of kudzu vine (Pueraria lobata), respectively. From this survey, our results indicate that the legumes, lupine (Lupinus spp.), fava bean, (Vicia faba), soybeans (Glycine max), kudzu (Pueraria lobata), and psoralea (Psoralea corylifolia), are excellent food sources for both genistein and daidzein. Miso, a fermented soybean product, is also a rich source of both isoflavones.




Curcumin and genistein, plant natural products, show synergistic inhibitory effects on the growth of human breast cancer MCF-7 cells induced by estrogenic pesticides.

Biochem Biophys Res Commun, 233(3):692-6 1997 Apr 28

Curcumin and genistein are two natural products of plants obtained from Curcuma longa Linn (turmeric) and soybeans, respectively. Both compounds when present at micromolar concentrations are able to inhibit the growth of estrogen-positive human breast MCF-7 cells induced individually or by a mixture of the pesticides endosulfane, DDT and chlordane or 17-beta estradiol. When curcumin and genistein were added together to MCF-7 cells, a synergistic effect resulting in a total inhibition of the induction of MCF-7 cells by the highly estrogenic activity of endosulfane/chlordane/DDT mixtures was noted. These data suggest that the combination of curcumin and genistein in the diet have the potential to reduce the proliferation of estrogen-positive cells by mixtures of pesticides or 17-beta estradiol. Since it is difficult to remove pesticides completely from the environment or the diet and since both turmeric and soybeans are not toxic to humans, their inclusion in the diet in order to prevent hormone related cancers deserves consideration.




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

Biochem Biophys Res Commun, 179(1):661-7 1991 Aug 30

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).




Bioavailability of soybean isoflavones depends upon gut microflora in women.

J Nutr, 125(9):2307-15 1995 Sep

Soybean isoflavones have been proposed to be anticarcinogenic, but their effective doses have not been established. To study their bioavailability, seven women consumed 3.4, 6.9, or 10.3 mumol isoflavones/kg body wt in soymilk in each of three meals of a liquid diet on one of three feeding days that were separated by 2-wk washout periods. Subjects were randomly assigned to doses in a cross-over design. Plasma, urine and fecal isoflavones were measured by reverse phase HPLC. In two subjects, fecal isoflavone recovery was 10-20 times that in the other five subjects. Average 48-h urinary recoveries of ingested daidzein and genistein were 16 +/- 4 and 10 +/- 4%, respectively, at all three doses among the five subjects excreting only small amounts of isoflavones in feces, whereas urinary recoveries of daidzein and genistein in the two subjects who excreted large amounts of fecal isoflavones were 32 +/- 5 and 37 +/- 6%, respectively. Urinary isoflavone excretion was nearly zero in all subjects at 48 h after dosing. Average plasma concentration of genistein at 24 h after the breakfast isoflavone dose in subjects excreting large amounts of fecal isoflavones was significantly greater by 2.5-fold than in subjects who excreted small amounts of fecal isoflavones (P < 0.05). In vitro anaerobic incubation of isoflavones with human feces showed that intestinal half-life of daidzein and genistein may be as little as 7.5 and 3.3 h, respectively. These data suggest that human isoflavone bioavailability depends upon the relative ability of gut microflora to degrade these compounds.




Rationale for the use of genistein-containing soy matrices in chemoprevention trials for breast and prostate cancer.

J Cell Biochem Suppl, 27(1):181-7 1995

Pharmacologists have realized that tyrosine kinase inhibitors (TKI) have potential as anti-cancer agents, both in prevention and therapy protocols. Nonetheless, concern about the risk of toxicity caused by synthetic TKIs restricted their development as chemoprevention agents. However, a naturally occurring TKI (the isoflavone genistein) in soy was discovered in 1987. The concentration of genistein in most soy food materials ranges from 1-2 mg/g. Oriental populations, who have low rates of breast and prostate cancer, consume 20-80 mg of genistein/day, almost entirely derived from soy, whereas the dietary intake of genistein in the US is only 1-3 mg/day. Chronic use of genistein as a chemopreventive agent has an advantage over synthetic TKIs because it is naturally found in soy foods. It could be delivered either in a purified state as a pill (to high-risk, motivated patient groups), or in the form of soy foods or soy-containing foods. Delivery of genistein in soy foods is more economically viable ($1.50 for a daily dose of 50 mg) than purified material ($5/day) and would require no prior approval by the FDA. Accordingly, investigators at several different sites have begun or are planning chemoprevention trials using a soy beverage product based on SUPRO, an isolated soy protein manufactured by Protein Technologies International of St. Louis, MO. These investigators are examining the effect of the soy beverage on surrogate intermediate endpoint biomarkers (SIEBs) in patients at risk for breast and colon cancer, defining potential SIEBs in patients at risk for prostate cancer, and determining whether the soy beverage reduces the incidence of cancer recurrence.




Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP.

Jpn J Clin Oncol, 208(1):360-3 1998 Jun

BACKGROUND: Epidemiological studies have suggested that soybean isoflavones are associated with a lower risk of prostate cancer. However, the mechanisms of prostate cancer prevention by soybean isoflavones have yet to be fully clarified. METHODS: Two soybean isoflavones (genistein and daidzein) and their glucosides (genistin and daidzin) were tested for their effects on cell growth and apoptosis of the LNCaP human prostatic cancer cell line. RESULTS: Among these isoflavones, genistein was found to inhibit the growth of LNCaP most effectively, with an IC50 value of 40 microM. The inhibition of cell growth by genistein was accompanied by the suppression of DNA synthesis and the induction of apoptosis. Expression of prostate-specific antigen (PSA) in LNCaP was also significantly reduced by the treatment with genistein. CONCLUSIONS: The results suggest that genistein might primarily influence human prostate cancer development by reducing tumor growth.




In vitro hormonal effects of soybean isoflavones.

J Nutr, 208(1):751S-756S 1995 Mar

Isoflavones exhibit a multitude of biological effects that influence cell growth and regulation, and, thus, may have potential value in the prevention and treatment of cancer. Isoflavones are weak estrogens and can function both as estrogen agonists and antagonists depending on the hormonal milieu and the target tissue and species under investigation. Genistein, one of the two primary isoflavones in soybeans, has attracted much attention from the research community, not only because of its potential antiestrogenic effects, but because it inhibits several key enzymes thought to be involved in carcinogenesis. Although still speculative, greater dietary incorporation of soybean products, because of the high concentration of isoflavones, may be a safe and effective means of reducing cancer risk.




Evolution of the health benefits of soy isoflavones.

Proc Soc Exp Biol Med, 208(1):386-92 1998 Mar

Soy is a unique dietary source of the isoflavones, genistein and daidzein. It has been part of the Southeast Asian diet for nearly five millenia, whereas consumption of soy in the United States and Western Europe has been limited to the 20th century. Heavy consumption of soy in Southeast Asian populations is associated with reduction in the rates of certain cancers and cardiovascular disease. Recent experimental evidence suggests that phytochemicals in soy are responsible for its beneficial effects, which may also include prevention of osteoporosis, a hereditary chronic nose bleed syndrome, and autoimmune diseases. Exposure of soy formula-fed infants to the potential estrogenizing effects of the isoflavones is limited by the first pass effect of the liver following the uptake of isoflavones from the gut. Several mechanisms of action of isoflavones have been proposed-both through estrogen-dependent and estrogen-independent pathways.




Antioxidant and antipromotional effects of the soybean isoflavone genistein.

Proc Soc Exp Biol Med, 208(1):124-30 1995 Jan

Antioxidant and antipromotional effects of the soybean isoflavone genistein have been studied in HL-60 cells and the mouse skin tumorigenesis model. Effects of structure-related flavone/isoflavones on hydrogen peroxide (H2O2) production by 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated HL-60 cells and superoxide anion (O2-) generation by xanthine/xanthine oxidase were compared. Of tested isoflavones, genistein is the most potent inhibitor among TPA-induced H2O2 formation by (dimethyl sulfoxide) DMSO-differentiated HL-60 cells, daidzein is second, and apigenin and biochanin A show little effect. In contrast, genistein, apigenin, and prunectin are equally potent in inhibiting O2- generation by xanthine/xanthine oxidase, with daidzein showing a moderate inhibitory effect and biochanin A exhibiting no effect. These results suggest that the antioxidant properties of isoflavones are structurally related and the hydroxy group at Position 4' is crucial in both systems. Dietary administration of 250 ppm genistein for 30 days significantly enhances the activities of antioxidant enzymes in the skin and small intestine of mice. Further studies show that genistein significantly inhibits TPA-induced proto-oncogene expression (c-fos) in mouse skin in a dose-dependent manner. In a two-stage skin carcinogenesis study, low levels of genistein (1 and 5 mumol) significantly prolong tumor latency and decrease tumor multiplicity by approximately 50%. We conclude that genistein's antioxidant properties and antiproliferative effects may be responsible for its anticarcinogenic effect. Its high content in soybeans and relatively high bioavailability favor genistein as a promising candidate for the prevention of human cancers.




Soy isoflavones improve systemic arterial compliance but not plasma lipids in menopausal and perimenopausal women.

Arterioscler Thromb Vasc Biol, 208(1):3392-8 1997 Dec

The possibility that the heightened cardiovascular risk associated with the menopause, which is said to be ameliorated by soybeans, can be reduced with soy isoflavones was tested in 21 women. Although several were perimenopausal, all have been included. A placebo-controlled crossover trial tested the effects of 80-mg daily isoflavones (45 mg genistein) over 5- to 10-week periods. Systemic arterial compliance (arterial elasticity), which declined with age in this group, improved 26% (P < .001) compared with placebo. Arterial pressure and plasma lipids were unaffected. The vasodilatory capacity of the microcirculation was measured in nine women; high acetylcholine-mediated dilation in the forearm vasculature was similar with active and placebo treatments. LDL oxidizability measured in vitro was unchanged. Thus, one important measure of arterial health, systemic arterial compliance, was significantly improved in perimenopausal and menopausal women taking soy isoflavones to about the same extent as is achieved with conventional hormone replacement therapy.




Synergistic action of quercetin and genistein in human ovarian carcinoma cells.

Oncol Res, 27(1):597-602 1997

Ovarian carcinoma is the fourth most common cause of cancer death in women and there has been a steady increase in the age-adjusted cancer death rates in the past 25 years in the US. However, patients who become cisplatin resistant respond poorly to available cytotoxic agents; therefore, discovering novel targets for ovarian carcinoma is vital. Quercetin, an anticancer agent, arrests the cell cycle at G1 and S phase boundary. Genistein, a plant flavonoid, attacks the cell cycle at G2 and/or early M phases in most carcinoma cells. Quercetin and genistein block the phosphatidylinositol conversion to IP3 signal transduction pathway mainly by inhibiting 1-phosphatidylinositol 4-kinase (PI kinase, EC 2.7.1.67) and 1-phosphatidylinositol 4-phosphate 5-kinase (PIP kinase, EC 2.7.1.68), respectively. Because each drug attacks a different phase of the cell cycle and reduces IP3 concentration by attacking different signal transduction enzymes, we tested the hypothesis that the two drugs might be synergistic in human carcinoma cells. In human ovarian carcinoma OVCAR-5 cells in growth inhibition assay, the IC50S for quercetin and genistein were (mean +/- SE) 66 +/- 3.0 and 32 +/- 2.5 microM; in clonogenic assays they were 15 +/- 1.2 and 5 +/- 0.5 microM, respectively. When quercetin was added to the cultures of OVCAR-5 cells followed 8 h later by genistein, synergism was observed in growth inhibition and clonogenic assays. The synergistic action of quercetin and genistein may be of interest in clinical treatment of human ovarian carcinoma.




Effect of structurally related flavones/isoflavones on hydrogen peroxide production and oxidative DNA damage in phorbol ester-stimulated HL-60 cells.

Nutr Cancer, 208(1):77-82 1997

We have examined the antioxidant properties of structurally related flavones/isoflavones in 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated HL-60 cells. In the presence of 1.3% dimethyl sulfoxide in the medium for seven days, promyelocytic HL-60 cells were differentiated into neutrophil-like cells possessing phagocytic properties and the capacity to generate H2O2 on TPA stimulation. The effects of five selected flavones/isoflavones on the formation of H2O2 and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were examined in TPA-stimulated HL-60 cells. The results indicated that genistein was the most potent inhibitor of H2O2 production by TPA-stimulated HL-60 cells, followed by apigenin and daidzein, whereas prunectin and biochanin A exhibited no effect. This inhibitory effect correlates well with the scavenging capacity of H2O2 by these flavones/isoflavones in an in vitro system. The formation of 8-OHdG in cellular DNA of HL-60 cells was induced by TPA and further enhanced by the addition of FeCl2 to the medium. Most flavones/isoflavones significantly inhibited TPA + FeCl2-induced 8-OHdG formation in HL-60 cells, with genistein being the most potent quencher. The inhibition of H2O2 production and 8-OHdG formation by these structurally related flavones/isoflavones may contribute to their chemopreventive potentials against human cancers.




Genistein inhibits both estrogen and growth factor-stimulated proliferation of human breast cancer cells.

Cell Growth Differ, 27(1):1345-51 1996 Oct

Genistein is a naturally occurring dietary protein tyrosine kinase (PTK) inhibitor that is hypothesized to be responsible for the lower rate of breast cancer observed in Asian women consuming soy. Although genistein is a potent in vitro PTK inhibitor, its mechanism of action in vivo is not known. In vivo, breast cancer growth is regulated by estrogens and peptide growth factors, such as epidermal growth factor (EGF), the receptor of which has intrinsic PTK activity. Therefore, genistein may block mammary epithelial cell growth by interfering with signal transduction events stimulated by estradiol or growth factors. The effect of genistein, related isoflavones, and other tyrosine kinase inhibitors on fetal bovine serum-, estradiol-, and EGF-stimulated cell growth and signal transduction pathways was examined in five human breast cancer cell lines. Genistein inhibited the growth of these cells by each of the growth stimuli with IC50 values ranging from 2.6 to over 20 micrograms/ml. Growth inhibition by genistein was cytostatic and reversible at IC50 concentrations. Related isoflavones were less potent growth inhibitors than genistein, whereas the synthetic PTK inhibitor tyrphostin A25 was an equally potent growth inhibitor. The mechanism of genistein growth inhibition in human breast cancer cells did not depend on the presence of functional estrogen receptor signaling pathways or on inhibition of EGF-receptor PTK activity. Furthermore, genistein (< or = 20 micrograms/ml) did not decrease constitutive or EGF-induced tyrosine phosphorylation as determined by Western blotting with antiphosphotyrosine antibodies. These data suggest that although genistein inhibits the growth of breast cancer cells in culture, it does so without gross inhibition of PTK activity.




Estrogenic and antiproliferative properties of genistein and other flavonoids in human breast cancer cells in vitro.

Nutr Cancer, 27(1):31-40 1997

Experimental and epidemiologic studies support the view that soyfoods prevent cancer as well as diseases and symptoms associated with estrogen deficiency. Recent research suggests that the isoflavonoid genistein, a phytoestrogen found in abundance in soyfoods, may be one of the principal molecular components responsible for these health benefits. In this study we investigated the effects of a broad physiologically relevant concentration range of genistein on estrogen receptor (ER) binding, induction of the estrogen-regulated antigen pS2, and cell proliferation rate in ER(+) and ER(-) human breast cancer cells grown in vitro. Dose response to genistein was compared with that of estradiol, tamoxifen, and several other structurally similar iso- and bioflavonoids (e.g., equol, kaempferol, and quercetin). Our results revealed that genistein has potent estrogen agonist and cell growth-inhibitory actions over a physiologically achievable concentration range (10 nM-20 microM). Other flavonoids over the same concentration range were good estrogen agonists and poor cell growth inhibitors (equol) or poor estrogen agonists and potent growth inhibitors (kaempferol and quercetin). The growth-inhibitory actions of flavonoids were distinctly different from those of triphenyl antiestrogens like tamoxifen. In summary, our results reveal that genistein is unique among the flavonoids tested, in that it has potent estrogen agonist and cell growth-inhibitory actions over a physiologically relevant concentration range.




Estrogen and progestin bioactivity of foods, herbs, and spices.

Proc Soc Exp Biol Med, 217(3):369-78 1998 Mar

In this study we report on the content and bioactivity of plant (phyto) estrogens and progestins in various foods, herbs, and spices, before and after human consumption. Over 150 herbs traditionally used by herbalists for treating a variety of health problems were extracted and tested for their relative capacity to compete with estradiol and progesterone binding to intracellular receptors for progesterone (PR) and estradiol (ER) in intact human breast cancer cells. The six highest ER-binding herbs that are commonly consumed were soy, licorice, red clover, thyme, tumeric, hops, and verbena. The six highest PR-binding herbs and spices commonly consumed were oregano, verbena, tumeric, thyme, red clover and damiana. Some of the herbs and spices found to contain high phytoestrogens and phytoprogestins were further tested for bioactivity based on their ability to regulate cell growth rate in ER (+) and ER (-) breast cancer cell lines and to induce or inhibit the synthesis of alkaline phosphatase, an end product of progesterone action, in PR (+) cells. In general, we found that ER-binding herbal extracts were agonists, much like estradiol, whereas PR-binding extracts, were neutral or antagonists. The bioavailability of phytoestrogens and phytoprogestins in vivo were studied by quantitating the ER-binding and PR-binding capacity of saliva following consumption of soy milk, exogenous progesterone, medroxyprogesterone acetate, or wild mexican yam products containing diosgenin. Soy milk caused a dramatic increase in saliva ER-binding components without a concomitant rise in estradiol. Consumption of PR-binding herbs increased the progestin activity of saliva, but there were marked differences in bioactivity. In summary, we have demonstrated that many of the commonly consumed foods, herbs, and spices contain phytoestrogens and phytoprogestins that act as agonists and antagonists in vivo.




Genistein, a dietary ingested isoflavonoid, inhibits cell proliferation and in vitro angiogenesis.

J Nutr, 27(1):790S-797S 1995 Mar

Consumption of a plant-based diet can prevent the development and progression of chronic diseases that are associated with extensive neovascularization. To determine whether prevention might be associated with dietary derived angiogenesis inhibitors, we have fractionated urine of healthy human subjects consuming a plant-based diet and examined the fractions for their abilities to inhibit the proliferation of vascular endothelial cells. One of the most potent fractions contained several isoflavonoids, which we identified by gas chromatography-mass spectrometry and subsequently synthesized. Of all synthetic compounds, the isoflavonoid genistein was the most potent and inhibited endothelial cell proliferation and in vitro angiogenesis at half maximal concentrations of 5 and 150 mumol/L, respectively. Moreover, genistein inhibited the proliferation of various tumor cells. Genistein excretion in urine of subjects consuming a plant-based diet is in the micromolar range, which is 30-fold higher than that of subjects consuming a traditional Western diet. The high concentrations of genistein in urine of vegetarians and our present results suggest that genistein may contribute to the preventive effect of plant-based diet on chronic diseases, including solid tumors, by inhibiting neovascularization and tumor cell proliferation. Thus genistein may have important applications in the treatment of solid tumors and angiogenic diseases.




Natural and synthetic isoflavones in the prevention and treatment of chronic diseases.

Calcif Tissue Int, 208(1):S5-8 1997

The evidence that natural isoflavones protect against several chronic diseases is both observational and experimental. In humans, epidemiologic findings clearly show a higher incidence of some common types of cancer (i.e., breast, prostate, and colon) and of coronary heart diseases in Western populations exposed to limited amounts of soybean isoflavones (i.e., genistein, daidzein) in the diet. Further evidence for cancer and cardiac protection and antiatherogenic effects resulting from soybean isoflavones administration has been noted in various experimental animal models. Isoflavones may also prevent postmenopausal bone loss and osteoporosis. In fact, genistein has been reported to be as active as estrogens in maintaining bone mass in ovariectomized rats. Moreover, the synthetic isoflavone derivative ipriflavone is able to reduce bone loss in various types of animal models of experimental osteoporosis providing a rationale on its use in the prevention and treatment of postmenopausal and senile osteoporosis in humans. The mechanism through which isoflavones may exert the above-mentioned effects seems to depend, at least in part, on their mixed estrogen agonist-antagonist properties. An alternative hypothetical mechanism could derive from other biochemical actions of isoflavones such as inhibition of enzymatic activity, in particular protein kinases, or activation of an "orphan" receptor distinct from the estrogen type I receptor.




A comparative survey of leguminous plants as sources of the isoflavones, genistein and daidzein: implications for human nutrition and health.

J Altern Complement Med, 208(1):7-12 1997 Spring

Over 80 taxa of mostly agriculturally important legumes were surveyed as sources of the metabolites, genistein and daidzein. Remarkably high concentrations (over 2 g.kg-1 dry weight) of the anticancer metabolite, genistein, were found in the leaves of Psoralea corylifolia (Indian bread root). All other legumes, with the exception of fermented soybean miso, had genistein levels < 400 mg.kg-1 dry weight. Concentrations of over 1 g.kg-1 dry weight and 0.95 g.kg-1 dry weight of the anticancer metabolite, daidzein, were found in the stems of the fava bean (Vicia faba) and roots of kudzu vine (Pueraria lobata), respectively. From this survey, our results indicate that the legumes, lupine (Lupinus spp.), fava bean, (Vicia faba), soybeans (Glycine max), kudzu (Pueraria lobata), and psoralea (Psoralea corylifolia), are excellent food sources for both genistein and daidzein. Miso, a fermented soybean product, is also a rich source of both isoflavones.




Curcumin and genistein, plant natural products, show synergistic inhibitory effects on the growth of human breast cancer MCF-7 cells induced by estrogenic pesticides.

Biochem Biophys Res Commun, 233(3):692-6 1997 Apr 28

Curcumin and genistein are two natural products of plants obtained from Curcuma longa Linn (turmeric) and soybeans, respectively. Both compounds when present at micromolar concentrations are able to inhibit the growth of estrogen-positive human breast MCF-7 cells induced individually or by a mixture of the pesticides endosulfane, DDT and chlordane or 17-beta estradiol. When curcumin and genistein were added together to MCF-7 cells, a synergistic effect resulting in a total inhibition of the induction of MCF-7 cells by the highly estrogenic activity of endosulfane/chlordane/DDT mixtures was noted. These data suggest that the combination of curcumin and genistein in the diet have the potential to reduce the proliferation of estrogen-positive cells by mixtures of pesticides or 17-beta estradiol. Since it is difficult to remove pesticides completely from the environment or the diet and since both turmeric and soybeans are not toxic to humans, their inclusion in the diet in order to prevent hormone related cancers deserves consideration.




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

Biochem Biophys Res Commun, 179(1):661-7 1991 Aug 30

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).