Showing papers on "Isoflavones published in 1996"

Flavonoids—Chemistry, metabolism, cardioprotective effects, and dietary sources

Abstract: Flavonoids are a group of polyphenolic compounds, diverse in chemical structure and characteristics, found ubiquitously in plants. Therefore, flavonoids are part of the human diet. Over 4,000 different flavonoids have been identified within the major flavonoid classes which include flavonols, flavones, flavanones, catechins, anthocyanidins, isoflavones, dihydroflavonols, and chalcones. Flavonoids are absorbed from the gastrointestinal tracts of humans and animals and are excreted either unchanged or as flavonoid metabolites in the urine and feces. Flavonoids are potent antioxidants, free radical scavengers, and metal chelators and inhibit lipid peroxidation. The structural requirements for the antioxidant and free radical scavenging functions of flavonoids include a hydroxyl group in carbon position three, a double bond between carbon positions two and three, a carbonyl group in carbon position four, and polyhydroxylation of the A and B aromatic rings. Epidemiological studies show an inverse correlation between dietary flavonoid intake and mortality from coronary heart disease (CHD) which is explained in part by the inhibition of low density lipoprotein oxidation and reduced platelet aggregability. Dietary intake of flavonoids range between 23 mg/day estimated in The Netherlands and 170 mg/day estimated in the USA. Major dietary sources of flavonoids determined from studies and analyses conducted in The Netherlands include tea, onions, apples, and red wine. More research is needed for further elucidation of the mechanisms of flavonoid absorption, metabolism, biochemical action, and association with CHD.

Soybean isoflavones improve cardiovascular risk factors without affecting the reproductive system of peripubertal rhesus monkeys.

Abstract: Although the beneficial effects of dietary soybean protein compared with animal proteins on plasma lipids, lipoproteins and atherosclerosis have been known for about 50 years, it has been uncertain whether these effects are due to its amino acid concentrations or other components in soybeans. To assess the effect of soybean protein's alcohol-extractable components (including the isoflavonic phytoestrogens genistein and daidzein) on plasma lipid and lipoprotein concentrations and to establish its lack of effect on the reproductive system, we fed 27 peripubertal male and female rhesus monkeys moderately atherogenic diets in which the source of dietary protein was a soy isolate (20% by weight), either containing phytoestrogens (also termed isoflavones) or with the phytoestrogens removed by alcohol extraction. The study was a crossover design with each period lasting for 6 mo. The phytoestrogen-intact soy protein (compared with the alcohol-extracted soy protein) had favorable effects on plasma lipid and lipoprotein concentrations, specifically by significantly reducing LDL+VLDL cholesterol concentrations in both males and females (approximately 30-40% lower), significantly increasing high density lipoprotein cholesterol (HDLC) concentrations for females (approximately 15% higher) and significantly lowering total plasma cholesterol (TPC):HDLC ratios (approximately 20% lower for males and 50% lower for females). The phytoestrogens had no adverse effects on the reproductive systems of either the males or females, as evaluated by reproductive hormone concentrations and organ weights at necropsy. Thus, the isoflavones in soy protein improve cardiovascular disease risk factors without apparent deleterious effects on the reproductive system of peripubertal rhesus monkeys.

Mass Balance Study of Isoflavones during Soybean Processing

Abstract: The effects of processing techniques on the distribution of isoflavones were investigated by manufacturing tempeh, soymilk, tofu, and protein isolate. The manufacturing steps causing significant losses (p < 0.05) of isoflavones were as follows: soaking (12%) and heat processing (49%) in tempeh production; coagulation (44%) in tofu processing; and alkaline extraction (53%) in soy protein isolate production. In the production of tempeh, soymilk, and tofu, malonyldaidzin and malonylgenistin decreased after soaking and cooking. Concomitantly, acetyldaidzin and acetylgenistin were generated during heat processing. After fermentation, daidzein and genistein concentrations increased in tempeh, apparently as a result of fungal enzymatic hydrolysis. In protein isolate processing, alkaline extraction caused the generation of daidzein and genistein, probably through alkaline hydrolysis. Keywords: Isoflavones; mass balance; soy protein isolate; tempeh; soymilk; tofu

Daidzein and genistein concentrations in human milk after soy consumption

Abstract: Soy isoflavones were quantified from human milk by a fast, precise, and selective HPLC method after enzymatic hydrolysis of conjugated isoflavones and extraction with ethyl acetate. Isoflavone aglycones and their mammalian metabolites equol and O-desmethylangolensin were separated selectively and identified by absorbance patterns, fluorometric and electrochemical detection, gas chromatography-mass spectrometric analysis after trimethylsilylation, and with internal and external authentic standards. HPLC injections of 20 microL of human milk showed detection limits of 1-3 pmol for all analytes by using diode-array detection. The detection limit could be improved by as much as 1000-fold by extended concentration through partitioning with ethyl acetate, by using electrochemical detection, by increasing the injection volumes, or by combining these techniques. We used the proposed method to monitor isoflavone concentrations in human milk and in human urine after challenge with 5, 10, and 20 g of roasted soybeans in the diet. Implications of the results for the potential of isoflavones to prevent cancer in newborn infants exposed to these agents are discussed.

Soy Isoflavonoids and Cancer Prevention

Abstract: The isoflavonoids in soy, genistein and daidzein, have been proposed to contribute an important part of the anti-cancer effect of soy. Although there have been many interesting studies on the effects of isoflavones on biochemical targets in tissue culture experiments, in most cases the concentrations used by investigators have exceeded 10 μM. However, based on simple pharmacokinetic calculations involving daily intake of isoflavones, absorption from the gut, distribution to peripheral tissues, and excretion, it is unlikely that blood isoflavone concentrations even in high soy consumers could be greater than 1–5 μM. Experiments designed to evaluate these pharmacological principles were carried out in anesthetized rats with indwelling biliary catheters and in human volunteers consuming soy beverages. The data from these experiments indicate that genistein is efficiently absorbed from the gut, taken up by the liver and excreted in the bile as its 7-O-β-glucuronide. Re-infused genistein 7-O-β-glucuronide was also well absorbed from the gut, although this occurred in the distal small intestine. In human subjects fed a soy beverage for a period of two weeks, plasma levels of genistein and daidzein, determined by HPLC-mass spectrometry, ranged from 0.55–0.86 μM, mostly as glucuronide and sulfate conjugates. In summary, genistein is well absorbed from the small intestine and undergoes an enterohepatic circulation. Although the plasma genistein levels achievable with soy food feeding are unlikely to be sufficient to inhibit the growth of mature, established breast cancer cells by chemotherapeutic-like mechanisms, these levels are sufficient to regulate the proliferation of epithelial cells in the breast and thereby may cause a chemopreventive effect.

Inhibition of N-methyl-N-nitrosourea-induced mammary tumors in rats by the soybean isoflavones.

Abstract: Soy-based diets, rich in the isoflavones genistein and daidzein, are thought to protect against breast and prostate cancer. We used the N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis animal model to test the effectiveness of these two isoflavones as chemopreventive agents. Each isoflavone was injected daily into 35-day-old rats for six months while we monitored the animals' body weight and mammary tumor appearance. Genistein was effective in reducing tumor multiplicity, but it reduced tumor incidence only marginally. Daidzein was less effective in reducing both tumor incidence and multiplicity. To investigate genistein's mechanism of action, we determined the topoisomerase II (topo II) activity and detected the phosphotyrosine-containing peptides in the extracts of mammary tissues isolated from control and isoflavone-treated animals. Mammary tumors contained over 60-fold higher topo II enzymatic activity than the mammary glands. Similarly, more tyrosine phosphopeptides were detectable in mammary tumors than in mammary glands. Tissue samples from genistein treated animals contained similar topo II and protein tyrosine kinase (PTK) activities as the control group. These data suggest that mammary tumorigenesis is accompanied by an extensive increase in topo II and PTK activities. The mechanism of chemoprevention by genistein. however, is independent of topo II or PTK inhibition.

The role of metabolism in mammary epithelial cell growth inhibition by the isoflavones genistein and biochanin A

Abstract: The basis for the differential sensitivity of cultured normal human mammary epithelial (HME) cells and a transformed human breast cancer MCF-7 cell line to growth inhibition by the isoflavone genistein and its 4'-methyl ether derivative, biochanin A, was examined. In HME cells genistein is 5-fold more potent as a growth inhibitor than biochanin A, whereas in MCF-7 cells biochanin A and genistein are equally potent as growth inhibitors. Based on its properties as an in vitro protein tyrosine kinase (PTK) inhibitor, biochanin A would be expected to be a less potent growth inhibitor than genistein. To determine whether isoflavone metabolism could account for the observed differences in growth inhibition, metabolism experiments were conducted with HME and MCF-7 cells using [4- 14 C]genistein and [4- 14 C]biochanin A. MCF-7 cells extensively metabolized both isoflavones, producing two genistein metabolites with molecular weights of 350 and 380 and three biochanin A metabolites with molecular weights of 270, 350 and 380. In contrast, significant genistein or biochanin A metabolism was not observed in HME cells. Using mass spectrometry and nuclear magnetic resonance analysis, metabolite 350 from genistein and biochanin A experiments was identified as genistein 7-sulfate ; biochanin A metabolite 270 was identified as genistein. Metabolite 380 was not unequivocally identified, but appeared to be a hydroxylated and methylated form of genistein sulfate. In MCF-7 cells, genistein 7-sulfate and metabolite 380 were detected primarily in the cell media fraction, suggesting that once formed these polar metabolites were excreted from the cells. These data show that isoflavone metabolism by transformed breast epithelial cells modulates the growth inhibitory effects of genistein and biochanin A. In MCF-7 cells, genistein metabolism was correlated with a decrease in growth inhibition, whereas biochanin A metabolism was associated with an increase in growth inhibition.

Altered kinetics and extent of urinary daidzein and genistein excretion in women during chronic soya exposure

Abstract: Soybean consumption may be protective for breast cancer, possibly due in part to the presence of the isoflavones daidzein and genistein, which are weakly estrogenic. The metabolism and disposition of these phytoestrogens during chronic soya exposure were studied on a metabolic unit. Six healthy 22‐ to 29‐year‐old women consumed an unrestricted hospital diet for most of the study and ingested 12 oz of soymilk with each meal for one month. At two‐week intervals, excretion of isoflavones in urine was studied, during which time the subjects consumed a constant basal diet for three to four days, ingested the full daily 36‐oz portion of soymilk within 30 minutes each day for one to two days, and collected urine continuously. Urinary recovery of genistein [initially 23.9 ± 17.3% (SD) of ingested genistin + genistein], daidzein (initially 66.2 ± 23.5% of ingested daidzin + daidzein), and equol (initially 28% of the ingested precursors daidzin + daidzein in 1 subject and <1% in 5 subjects) decreased progr...

A Diet High in Wheat Fiber Decreases the Bioavailability of Soybean Isoflavones in a Single Meal Fed to Women

Abstract: The absorption of some dietary components may be inhibited by dietary fiber. To study the effect of dietary fiber on the bioavailability of Isoflavones, seven healthy women were randomly assigned in a crossover design to a control diet containing 15 g dietary fiber or a wheat fiber-supplemented diet containing 40 g dietary fiber, both fed with a single dose of 0.9 mg isoflavones/kg body weight from tofu or texturized vegetable protein (TVP). The fiber-rich diet produced 55% lower plasma genistein at 24 h after soy dosing (P < 0.05) and reduced total urinary genistein by 20% (P < 0.03). Urinary daidzein was not significantly related to fiber intake. Highly insoluble, dietary wheat fiber reduced the absorption of genistein probably by its bulking effect and hydrophobic binding to this compound. Urinary genistein was greater by 23% after tofu than after TVP consumption (P < 0.02), but the percentage of ingested genistein recovered in urine was not affected by soy product intake. The higher urinary genistein after tofu consumption compared with TVP was apparently due to differences in amount of genistein between these soy foods, not the different forms of genistein present in these two soy food products.

Chemotactic Preferences and Strain Variation in the Response of Phytophthora sojae Zoospores to Host Isoflavones.

Abstract: The zoospores of Phytophthora sojae are chemotactically attracted to the isoflavones genistein and daidzein that are released by soybean roots In this study we have examined the response of P sojae zoospores to a wide range of compounds having some structural similarity to genistein and daidzein, including isoflavones, flavones, chalcones, stilbenes, benzoins, benzoates, benzophenones, acetophenones, and coumarins Of 59 compounds examined, 43 elicited some response A comparison of the chemotactic responses elicited by the various compounds revealed a primary role for the phenolic 4(prm1)- and 7-hydroxyl groups on the isoflavone structure A few compounds acted as repellents, notably methylated flavones with a hydrophobic B ring The chemotactic response to many of the analogs was markedly different among different strains of P sojae

Supercritical Carbon Dioxide Extraction of Daidzein and Genistein from Soybean Products

Abstract: The extractibility of isoflavones by supercritical carbon dioxide was studied by extracting synthetically produced daidzein (1), genistein (2), formononetin (3) and biochanin A (4). Supercritical fluid carbon dioxide (SFCO2) modified with 20% ethanol at 50° and 600 atmospheres pressure extracted nearly 93% of these isoflavones in 60 min. Daidzein and genistein were extracted by SFCO2 and quantified by high performance liquid chromatography in the extracts of soybean food products, miso, tofu, soy meal and soy flour; the amounts of 1 and 2 (expressed in μg/g dry weight) in these foods were found to be 42, 61; 20, 20; 40, 8 and 10, 5, respectively. This is the first report of supercritical carbon dioxide extraction of 1 and 2 from soy products.

Process for isolating phytoestrogens from plant protein

Abstract: The present invention relates generally to a method of isolating phytoestrogens isoflavones from plant material. More specifically, this invention is directed to a method of using ion exchange technology to isolate phytoestrogens from plant protein isolates and to the phytoestrogen so isolated.

Minor Dietary Factors in Relation to Coronary Heart Disease Flavonoids, Isoflavones and Boron

Abstract: Flavonoids are potent inhibitors of the oxidative modification of low-density lipoprotein (LDL), and foods containing these compounds have been shown to be negatively associated with coronary heart disease (CHD). Flavonoids reduce the formation of free radicals and protect or regenerate other antioxidants; or alternatively, they chelate divalent metal ions. Isoflavones may act in a manner similar to estrogen in that they lower LDL and in this way confer protection against CHD. Less is known about other minor dietary constituents, such as boron, which is widespread in fruits and vegetables. Boron may have an impact on CHD by inducing small increases in the concentration of plasma estrogen.

Genetic status of p53 and induction of apoptosis by radiation or isoflavones in human gastric carcinoma cell lines.

Abstract: We have shown previously that various human cancer cell lines undergo morphological changes and internucleosomal DNA fragmentation characteristic of apoptosis after exposure to ionizing radiation or isoflavones. Here, we assessed the role of p53 gene in cell cycle and apoptosis following treatment of 11 gastric carcinoma cell lines with gamma-rays, genistein, biochanin A, or daidzein. Cell survival was measured by trypan blue staining, and apoptosis was assessed by fluorochrome staining. The rate of cell survival and apoptosis of the cells by gamma-irradiation or isoflavones did not correlate with p53 gene abnormalities. Flow cytometric measurement of DNA content demonstrated that while gamma-irradiation and genistein induced G(2) arrest, biochanin A and daidzein blocked the cell cycle of all carcinoma cells at G(1) phase. At multiple time points following irradiation, G(2) arrest was observed at 12-16 h in the wild-type and mutant p53 cell lines. Induction of p53 and p21 proteins was not observed in wild-type p53 lines after exposure to gamma-irradiation or isoflavones by Western blotting. Moreover, transfection of the wild-type p53 gene into MKN-1 cells failed to induce G(1) arrest by gamma-irradiation and genistein. Based on these results, we hypothesize that gastric cancer cells may possess a signal pathway which is different from the usual mechanisms of the p53-mediated DNA damage response in normal or hematopoietic tumor cells.

Physiological Function of Isoflavones and Their Genetic and Environmental Variations in Soybean

Abstract: Soyfoods have potential roles in the prevention and treatment of chronic diseases, most notably cancer, osteoporosis, and heart disease. There is evidence that carcinogenesis are supressed by isolated soybean derived products in vivo such as a protease inhibitor, phytic acid, saponins and isoflavones. It is believed that supplementation of human diets with soybean products markedly reduces human cancer mortality rates. Especially, recent papers recognize the potential benefit of soybean isoflavone components for reducing the risk of various cancers. Isoflavones exhibit a multitude of medicinal effects that influence cell growth and regulation, which may have potential value in the prevention and treatment of cancer. In addition to potential biological effects, soybean isoflavones have the important physiological functions such as the induction of Bradyrizobium japonicum nod genes and the responses of soybean tissues to infection by Phytophthora megasperma as well as biochemical activities such as antifungal and antibacterial actions. Genistin, daidzin, glycitin and their aglycone (genistein, daidzein, glycitein) are the principal isoflavones found in soybean. Malonyl and acetyl forms have also been detected but they are thermally unstable and are usually transformed during the processing in glucoside form. Most soy products, with the exception of soy sauce, alcohol-extracted soy protein concentrate, and soy protein isolate, have total isoflavone concentrations similar to those in the whole soybean. Soybean-containing diets inhibit mammary tumorigenesis in animal models of breast cancer, therefore, it is possible that dietary isoflavones are an important factor accounting for the lower incidence and mortality from breast cancer. Of the total soybean seed isoflavones, were located in cotyledons, with the remainder in the hypocotyls. The hypocotyls had a higher concentrations of isoflavones on a weight basis compared with cotyledons. Isoflavone contents were influenced by genetics, crop years, and growth locations. The effect of crop year had a greater impact on the isoflavone contents than that of location. The climate condition might be the attribution factor to variation in isoflavone contents. Also, while the isoflavone content of cotyledons exhibited large variations in response to high temperature during seed development, hypocotyls showed high concentration in isoflavone content. So, it is concluded that one of the factors affecting isoflavone content in soybean seeds is temperature during seed development. High temperature, especially in maturity stage, causes lower isoflavone content in soybean seed. It is also suggested that there may exist a different mechanism to maintain isoflavone contents between cotyledon and seed hypocotyls. In a conclusion, soy foods may be able to have a significant beneficial impact on public health.

Some Flavones and Isoflavones as Inhibitors of Human Placental 17β‐Hydroxysteroid Dehydrogenase In‐vitro

Abstract: Oestrogen-dependent breast cancers are considered to produce oestradiol in the breast through the initial action of a sulphatase on the oestrone sulphate reservoir, followed by reduction of the oestrone formed by a 17β-hydroxysteroid dehydrogenase. The low rate of incidence of the disease in the Far East has been related to a high dietary intake of soya products containing flavones and isoflavones. We have found that the flavones chrysin (IC50 60-5 μM), apigenin (18-3 μM) and naringenin (19-9 μM), and the isoflavones genistein (195 μM), biochanin A (47-6 μM) and daidzein are potent inhibitors of human placental 17 β-hydroxy steroid dehydrogenase.