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Researches of Phytoestrogens

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Soyfoods and soybean phyto-estrogens (Isoflavones) as possible alternatives to hormone replacement therapy (HRT)

Author: M. Messina * Nutrition Matters, Inc. Port Townsend, WA 98368, USA

Soya is now widely investigated for its role in chronic disease prevention. Early interest in this field was fueled by the lower rates of coronary heart disease (CHD) and breast and prostate cancer in Asia. Numerous in vitro, animal, and clinical studies now provide a solid basis for continued investigation. In addition to cancer and CHD, there are data suggesting soya may reduce the risk of osteoporosis and help to alleviate menopausal symptoms. Consequently, soya is viewed as a possible alternative to hormone replacement therapy (HRT).

Focus on soya is due largely to the high concentra- tions of isoflavones in soybeans. isoflavones are diphe- nolic compounds and are a subclass of the more ubiquitous flavonoids. The primary isoflavones in soy- beans are genistein and daidzein. isoflavone content varies among soybean varieties but is approximately 1±4 mg/g. Average daily isoflavone intake in Asia is approxi- mately 10±40 mg. In subjects consuming approximately 100 mg of isoflavones from soyfoods, serum isoflavone levels as high as 6 umol have been achieved.

Isoflavones are weakly oestrogenic. Depending upon the assay employed isoflavones possess between 1x10(-4) and 1x10(-2) the activity of 17b-oestradiol on a molar basis. However, genistein binds with 5 to 20 times more affinity to the oestrogen receptor (ER)b than ERa. The greater binding affinity of isoflavones to ERb than ERa suggests that isoflavones may be tissue selective in their effects. Furthermore, some data suggest isoflavones can function as anti-oestrogens in some situations. Consequently, some researchers consider isoflavones to be natural selective oestrogen receptor modulators (SERMs).

Although isoflavones are phyto-oestrogens, the physiological effects of isoflavones, especially genistein, are likely only partially related to direct interaction with or binding to ERs. This is evidenced by the finding that genistein inhibits the growth of a wide range of both hormone dependent and independent cancer cells in vitro - a result thought to be due to the ability of genistein to influence signal transduction pathways.

Published: 2000

Use of alternative therapies in menopause

Authors: Michelle P. Warren MD, Professor of Medicine and Obsterics and Gynecology, Department of Obstetrics and Gynecology, Columbia University, New York, USA
Center for Menopause, Hormonal Disorders and Women's Health, Columbia-Presbyterian Medical Center, New York, USA
Barbara Shortle MD, Assistant Professor of Obstetrics and Gynecology Center for Menopause, Hormonal Disorders and Women's Health, Columbia-Presbyterian Medical Center, New York, USA
Jennifer E. Dominguez, Research Assistant Department of Obstetrics and Gynecology, Columbia University, New York, USA

Objective: Hormone replacement therpy has traditionally been used to treat the accompanying symptoms of oestrogen deficiency in menopause. However, not all women can, or prefer to, receive this treatment and alternatives should be considered to reduce the increased risk of osteoporosis and heart disease in menopausal women. This chapter reviews the current literature on the efficacy of phyto-oestrogens in preventing cardiovascular disease, various cancers and osteoporosis, as well as treating the vasomotor and other menopause-related symptoms. Select herbal therapies, as well as selective oestrogen receptor modulators, are also considered.

Published: N/A
Keywords: breast neoplasms, cardiovascular diseases, colonic neoplasms, endometrial neoplams, herbs, isoflavones, lignans, menopause, osteoporosis, phyto-oestrogens, selective oestrogen receptor modulators, soy protein

Neurobehavioral effects of dietary soy phytoestrogens

Authors: Edwin D. Lephart,a,*, Timothy W. West,a, K. Scott Weber,a, Reuben W. Rhees,a, Kenneth D.R. Setchell,b, Herman Adlercreutz,c, Trent D. Lund,a
a. Neuroscience Center, 633 WIDB, Brigham Young University, Provo, UT 86402, USA
b. Clinical Mass Spectrometry, Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
c. Institute for Preventive Medicine, Nutrition, and Cancer, Folkha¨lsan Research, Center, and Division of Clinical Chemistry, University of Helsinki, Helsinki, Finland

Phytoestrogens, plant-derived nonsteroidal estrogens found in high abundance in most soy food products, have been studied for their potential beneficial effects against hormone-dependent cancers and age-related diseases. However, little is known about the influence of phytoestrogens on the brain or behavior. This brief review describes mainly our own studies in rodents that have examined the influence of dietary soy isoflavones on certain aspects of brain structure, learning, memory and anxiety along with the brain androgen-metabolizing enzyme, aromatase. These studies used a commercially available diet rich in phytoestrogens (Phyto-rich) vs. a custom diet relatively free of phytoestrogens (Phyto-free). The phytoestrogen content of each diet was determined by high-performance liquid chromatography analysis, circulating plasma phytoestrogen levels were quantified by gas chromatography mass spectroscopy and oncentrations of phytoestrogens in specific brain regions were measured by time-resolved fluoroimmunoassay (TR-FIA). Our studies showed that brain aromatase levels were not significantly altered by phytoestrogen diet treatments in perinatal, maternal or adult rats. However, volumes of the sexually dimorphic nucleus of the preoptic area (SDN-POA) were significantly affected by the Phyto-free diet treatment in male rats during adulthood, where SDN-POA volumes were smaller compared to Phyto-rich male values. Additionally, the Phyto-rich diet fed to adult male and female rats produced anxiolytic effects as assessed in the elevated plus maze vs. Phyto-free fed animals. Finally, when learning and memory parameters were examined in a radial arm maze testing visual–spatial memory (VSM), the diet treatments significantly changed the typical sexually dimorphic pattern of VSM. Specifically, adult Phyto-rich fed females outperformed Phyto-free fed females, while in males on the same diets, the opposite pattern of maze performance was observed. When female vs. male performance was compared, Phyto-rich females executed the VSM task in a manner similar to that of Phyto-free fed males, while Phytofree fed female’s VSM was comparable to Phyto-rich males. These results indicate that consumption of dietary phytoestrogens resulting in very high plasma isoflavone levels (in many cases over a relatively short interval of consumption in adulthood) can significantly alter sexually dimorphic brain regions, anxiety, learning and memory. The findings of these studies identify the biological actions of phytoestrogens, specifically isoflavones and their metabolites, found in animal soy-containing diets on brain and behavior and implicate the importance of phytoestrogens given the recognized significance of estrogens in brain and neural disorders, such as Alzheimer’s disease, especially in women.

Published: 26 October 2001
Keywords: Phytoestrogens; Radial arm maze; Elevated plus maze; Brain aromatase; Rat
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