Dietary soy phytoestrogen effects on brain structure and aromatase in Long-Evans rats

Neuron-Derived Estrogen-A Key Neuromodulator in Synaptic Function and Memory

In addition to being a steroid hormone, 17β-estradiol (E₂) is also a neurosteroid produced in neurons in various regions of the brain of many species, including humans. Neuron-derived E₂ (NDE₂) is synthesized from androgen precursors via the action of the biosynthetic enzyme aromatase, which is located at synapses and in presynaptic terminals in neurons in both the male and female brain. In this review, we discuss evidence supporting a key role for NDE₂ as a neuromodulator that regulates synaptic plasticity and memory. Evidence supporting an important neuromodulatory role of NDE₂ in the brain has come from studies using aromatase inhibitors, aromatase overexpression in neurons, global aromatase knockout mice, and the recent development of conditional forebrain neuron-specific knockout mice. Collectively, these studies demonstrate a key role of NDE₂ in the regulation of synapse and spine density, efficacy of excitatory synaptic transmission and long-term potentiation, and regulation of hippocampal-dependent recognition memory, spatial reference memory, and contextual fear memory. NDE₂ is suggested to achieve these effects through estrogen receptor-mediated regulation of rapid kinase signaling and CREB-BDNF signaling pathways, which regulate actin remodeling, as well as transcription, translation, and transport of synaptic proteins critical for synaptic plasticity and function.

Brain-derived estrogen and neural function

Although classically known as an endocrine signal produced by the ovary, 17β-estradiol (E₂) is also a neurosteroid produced in neurons and astrocytes in the brain of many different species. In this review, we provide a comprehensive overview of the localization, regulation, sex differences, and physiological/pathological roles of brain-derived E₂ (BDE₂). Much of what we know regarding the functional roles of BDE₂ has come from studies using specific inhibitors of the E₂ synthesis enzyme, aromatase, as well as the recent development of conditional forebrain neuron-specific and astrocyte-specific aromatase knockout mouse models. The evidence from these studies support a critical role for neuron-derived E₂ (NDE₂) in the regulation of synaptic plasticity, memory, socio-sexual behavior, sexual differentiation, reproduction, injury-induced reactive gliosis, and neuroprotection. Furthermore, we review evidence that astrocyte-derived E₂ (ADE₂) is induced following brain injury/ischemia, and plays a key role in reactive gliosis, neuroprotection, and cognitive preservation. Finally, we conclude by discussing the key controversies and challenges in this area, as well as potential future directions for the field.

Isoflavones derived from plant raw materials: bioavailability, anti-cancer, anti-aging potentials, and microbiome modulation

Isoflavones are secondary metabolites that represent the most abundant category of plant polyphenols. Dietary soy, kudzu, and red clover contain primarily genistein, daidzein, glycitein, puerarin, formononetin, and biochanin A. The structural similarity of these compounds to β-estradiol has demonstrated protection against age-related and hormone-dependent diseases in both genders. Demonstrative shreds of evidence confirmed the fundamental health benefits of the consumption of these isoflavones. These relevant activities are complex and largely driven by the source, active ingredients, dose, and administration period of the bioactive compounds. However, the preclinical and clinical studies of these compounds are greatly variable, controversial, and still with no consensus due to the non-standardized research protocols. In addition, absorption, distribution, metabolism, and excretion studies, and the safety profile of isoflavones have been far limited. This highlights a major gap in understanding the potentially critical role of these isoflavones as prospective replacement therapy. Our general review exclusively focuses attention on the crucial role of isoflavones derived from these plant materials and critically highlights their bioavailability, possible anticancer, antiaging potentials, and microbiome modulation. Despite their fundamental health benefits, plant isoflavones reveal prospective therapeutic effects that worth further standardized analysis.

Genistein during Development Alters Differentially the Expression of POMC in Male and Female Rats

Phytoestrogens are considered beneficial for health, but some studies have shown that they may cause adverse effects. This study investigated the effects of genistein administration during the second week of life on energy metabolism and on the circuits regulating food intake. Two different genistein doses, 10 or 50 µg/g, were administered to male and female rats from postnatal day (P) 6 to P13. Physiological parameters, such as body weight and caloric intake, were then analyzed at P90. Moreover, proopiomelanocortin (POMC) expression in the arcuate nucleus (Arc) and orexin expression in the dorsomedial hypothalamus (DMH), perifornical area (PF) and lateral hypothalamus (LH) were studied. Our results showed a delay in the emergence of sex differences in the body weight in the groups with higher genistein doses. Furthermore, a significant decrease in the number of POMC-immunoreactive (POMC-ir) cells in the Arc in the two groups of females treated with genistein was observed. In contrast, no alteration in orexin expression was detected in any of the structures analyzed in either males or females. In conclusion, genistein can modulate estradiol's programming actions on the hypothalamic feeding circuits differentially in male and female rats during development.

The effects of different dietary protein sources on live weight, sperm quality and the histology of the testes and accessory glands in male rats

This study was aimed at determining the effects of corn and wheat gluten, used as dietary protein sources, on live weight gain, sperm quality and the histology of the testes and accessory glands in male rats. For this purpose, 20-day-old 24 male Wistar albino rats were randomly assigned to three groups. Group 1 (Control), Group 2 and Group 3 were fed on a basal ration supplemented with high levels of soybean meal, corn gluten and wheat gluten, respectively, as a protein source. At the end of the study, when compared to Group 1, live weight values were determined to have increased in Group 3 and to have decreased in Group 2 (p < .05). Furthermore, sperm density, sperm motility, the dead/ live sperm ratio and testes weight were determined to have significantly decreased in Group 2, in comparison to Groups 1 and 3 (p < .05). The percentages of abnormal spermatozoon, and head, acrosome, mid-piece and tail abnormalities were high in Group 2 (p < .05). Histological examination demonstrated that, in Group 2, the diameter of the Tubulus Seminiferous Contortus (TSC) and the size of the Tubular Epithelial Cells (TE) were small, and the tubular and anatomical structure of the testes were shrunken and altered. Group 2 also presented with connective tissue increase and alveolar lumen enlargement in the prostate gland, and with connective tissue thickening, muscle tissue increase and secretory capacity decrease in the seminal vesicle (p < .05). Moreover, in Group 2, the Gl. Bulbourethral (Cowper's gland) presented with a decreased size and dilatations in the mucous structures. In a result, based on the findings obtained in this study, it is suggested that high levels of dietary corn gluten adversely affect live weight, sperm quality, and the testes and accessory glands.

Sexual hormones regulate the redox status and mitochondrial function in the brain. Pathological implications

Compared to other organs, the brain is especially exposed to oxidative stress. In general, brains from young females tend to present lower oxidative damage in comparison to their male counterparts. This has been attributed to higher antioxidant defenses and a better mitochondrial function in females, which has been linked to neuroprotection in this group. However, these differences usually disappear with aging, and the incidence of brain pathologies increases in aged females. Sexual hormones, which suffer a decrease with normal aging, have been proposed as the key factors involved in these gender differences. Here, we provide an overview of redox status and mitochondrial function regulation by sexual hormones and their influence in normal brain aging. Furthermore, we discuss how sexual hormones, as well as phytoestrogens, may play an important role in the development and progression of several brain pathologies, including neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, stroke or brain cancer.

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Sex hormones are reduced with aging, especially in females, affecting redox balance.

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Normal aging is associated to a worse redox homeostasis in the brain.

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Young females show better mitochondrial function and higher antioxidant defenses.

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Development of brain pathologies is influenced by sex hormones and phytoestrogens.

Dietary phytoestrogens modulate aggression and activity in social behavior circuits of male mice

Phytoestrogens comprise biologically active constituents of human and animal diet that can impact on systemic and local estrogen functions in the brain. Here we report on the importance of dietary phytoestrogens for maintaining activity in a brain circuit controlling aggressive and social behavior of male mice. After six weeks of low-phytoestrogen chronic diet (diadzein plus genistein <20 μg/g) a reduction of intermale aggression and altered territorial marking behavior could be observed, compared to littermates on a standard soy-bean based diet (300 μg/g). Further, mice on low-phyto diet displayed a decrease in sociability and a reduced preference for social odors, indicating a general disturbance of social behavior. Underlying circuits were investigated by analysing the induction of the activity marker c-Fos upon social encounter. Low-phyto diet led to a markedly reduced c-Fos induction in the medial as well as the cortical amygdala, the lateral septum, medial preoptic area and bed nucleus of the stria terminalis. No difference between groups was observed in the olfactory bulb. Together our data suggest that dietary phytoestrogens critically modulate social behavior circuits in the male mouse brain.

Mini-review: Epigenetic mechanisms that promote transgenerational actions of endocrine disrupting chemicals: Applications to behavioral neuroendocrinology

It is our hope this mini-review will stimulate discussion and new research. Here we briefly examine the literature on transgenerational actions of endocrine disrupting chemicals (EDCs) on brain and behavior and their underlying epigenetic mechanisms including: DNA methylation, histone modifications, and non-coding RNAs. We stress that epigenetic modifications need to be examined in a synergistic manner, as they act together in situ on chromatin to change transcription. Next we highlight recent work from one of our laboratories (VGC). The data provide new evidence that the sperm genome is poised for transcription. In developing sperm, gene enhancers and promoters are accessible for transcription and these activating motifs are also found in preimplantation embryos. Thus, DNA modifications associated with transcription factors during fertilization, in primordial germ cells (PGCs), and/or during germ cell maturation may be passed to offspring. We discuss the implications of this model to EDC exposures and speculate on whether natural variation in hormone levels during fertilization and PGC migration may impart transgenerational effects on brain and behavior. Lastly we discuss how this mechanism could apply to neural sexual differentiation.

Depletion of dietary phytoestrogens reduces hippocampal plasticity and contextual fear memory stability in adult male mouse

Introduction: Phytoestrogens are non-steroidal estrogen analogues and are found primarily in soy products. They have received increasing attention as dietary supplements for estrogen deficiency and as modulators of endogenous estrogen functions, including cognition and emotion. In addition to modifying the levels of circulating sex hormones, phytoestrogens also exert direct effects on estrogen and androgen receptors in the brain and thus effectively modulate the neural circuit functions.Objective: The aim of this study was to investigate the long-term effects of low phytoestrogen intake (∼6 weeks) on the hippocampal plasticity and hippocampus-dependent memory formation in the adult C57BL/6 male mice.Methods and Results: In comparison to mice on a diet with normal phytoestrogen content, mice on low phytoestrogen diet showed a significant reduction in the phosphorylation of NR2B subunit, a molecular correlate of plasticity in the Schaffer collateral-CA1 synapse. We observed a profound decrease in long-term potentiation (LTP) in the ventral hippocampus, whereas no effect on plasticity was evident in its dorsal portion. Furthermore, we demonstrated that acute perfusion of slices with an estrogen analogue equol, an isoflovane metabolized from daidzein produced by the bacterial flora in the gut, was able to rescue the observed LTP deficit. Examining potential behavioral correlates of the plasticity attenuation, we found that mice on phytoestrogen-free diet display decreased contextual fear memory at remote but not at recent time points after training.Conclusions: Our data suggests that nutritional phytoestrogens have profound effects on the plasticity in the ventral hippocampus and ventral hippocampus-dependent memory.

Gut microbiota derived metabolites in cardiovascular health and disease

Trillions of microbes inhabit the human gut, not only providing nutrients and energy to the host from the ingested food, but also producing metabolic bioactive signaling molecules to maintain health and elicit disease, such as cardiovascular disease (CVD). CVD is the leading cause of mortality worldwide. In this review, we presented gut microbiota derived metabolites involved in cardiovascular health and disease, including trimethylamine-N-oxide (TMAO), uremic toxins, short chain fatty acids (SCFAs), phytoestrogens, anthocyanins, bile acids and lipopolysaccharide. These gut microbiota derived metabolites play critical roles in maintaining a healthy cardiovascular function, and if dysregulated, potentially causally linked to CVD. A better understanding of the function and dynamics of gut microbiota derived metabolites holds great promise toward mechanistic predicative CVD biomarker discoveries and precise interventions.

Selective regulation of neurosteroid biosynthesis under ketamine-induced apoptosis of cortical neurons in vitro

Numerous studies have suggested that ketamine administration can induce neuroapoptosis in primary cultured cortical neurons. Neurosteroids modulate neuronal function and serve important roles in the central nervous system, however the role of neurosteroids in neuroapoptosis induced by ketamine remains to be elucidated. The present study aimed to explore whether neurosteroidogenesis was a pivotal mechanism for neuroprotection against ketamine-induced neuroapoptosis, and whether it may be selectively regulated under ketamine-induced neuroapoptosis conditions in primary cultured cortical neurons. To study this hypothesis, the effect of ketamine exposure on neurosteroidogenesis in primary cultured cortical neurons was investigated. Cholesterol, a substrate involved in the synthesis of neurosteroids, was added to the culture medium, and neurosteroids were quantified using high-performance liquid chromatography-tandem mass spectrometry analysis. The data demonstrated that cholesterol blocked ketamine-induced neuroapoptosis by promoting the synthesis of various neurosteroids, and the pathway of neurosteroid testosterone conversion into estradiol was inhibited by ketamine exposure. These data suggest that endogenous neurosteroids biosynthesis is critical for neuroprotection against ketamine-induced neuroapoptosis and inhibiting the biosynthesis of neuroprotective-neurosteroid estradiol is of notable importance for ketamine-induced neuroapoptosis.

Transcriptional regulation of glutamic acid decarboxylase in the male mouse amygdala by dietary phyto-oestrogens

Phyto-oestrogens are biologically active components of many human and laboratory animal diets. In the present study, we investigated, in adult male mice with C57BL/6 genetic background, the effects of a reduced phyto-oestrogens intake on anxiety-related behaviour and associated gene expression in the amygdala. After 6 weeks on a low-phyto-oestrogen diet (< 20 μg/g cumulative phyto-oestrogen content), animals showed reduced centre exploration in an open-field task compared to their littermates on a soybean-based standard diet (300 μg/g). Freezing behaviour in an auditory fear memory task, in contrast, was not affected. We hypothesised that this mildly increased anxiety may involve changes in the function of GABAergic local circuit neurones in the amygdala. Using GAD67(+/GFP) mice, we could demonstrate reduced transcription of the GAD67 gene in the lateral and basolateral amygdala under the low-phyto-oestrogen diet. Analysis of mRNA levels in microdissected samples confirmed this regulation and demonstrated concomitant changes in expression of the second glutamic acid decarboxylase (GAD) isoform, GAD65, as well as the anxiolytic neuropeptide Y. These molecular and behavioural alterations occurred without apparent changes in circulating oestrogens or testosterone levels. Our data suggest that expression regulation of interneurone-specific gene products in the amygdala may provide a mechanism for the control of anxiety-related behaviour through dietary phyto-oestrogens.

Neuroprotective effects of daidzein on focal cerebral ischemia injury in rats

Daidzein, a plant extract, has antioxidant activity. It is hypothesized, in this study, that daidzein exhibits neuroprotective effects on cerebral ischemia. Rat models of middle cerebral artery occlusion were intraperitoneally administered daidzein. Biochemical and immunohistochemical tests showed that superoxide dismutase and nuclear respiratory factor 1 expression levels in the brain tissue decreased after ischemia and they increased obviously after daidzein administration; malondialdehyde level and apoptosis-related cysteine peptidase caspase-3 and caspase-9 immunoreactivity in the brain tissue increased after ischemia and they decreased obviously after daidzein administration. Hematoxylin-eosin staining and luxol fast blue staining results showed that intraperitoneal administration of daidzein markedly alleviated neuronal damage in the ischemic brain tissue. These findings suggest that daidzein exhibits neuroprotective effects on ischemic brain tissue by decreasing oxygen free radical production, which validates the aforementioned hypothesis.

Changes of growth hormone-releasing hormone and somatostatin neurons in the rat hypothalamus induced by genistein: a stereological study

OBJECTIVES

Genistein is a plant-derived estrogenic isoflavone commonly found in dietary and therapeutic supplements, due to its potential health benefits. Growth hormone-releasing hormone (GHRH) and somatostatin (SS) are neurosecretory peptides synthesized in neurons of the hypothalamus and regulate the growth hormone secretion. Early reports indicate that estrogens have highly involved in the regulation of GHRH and SS secretions. Since little is known about the potential effects of genistein on GHRH and SS neurons, we exposed rats to genistein.

METHODS

Genistein were administered to adult rats in dose of 30 mg/kg, for 3 weeks. The estradiol-dipropionate treatment was used as the adequate controls to genistein. Using applied stereology on histological sections of hypothalamus, we obtained the quantitative information on arcuate (Arc) and periventricular (Pe) nucleus volume and volume density of GHRH neurons and SS neurons. Image analyses were used to obtain GHRH and SS contents in the median eminence (ME).

RESULTS

Administration of estradiol-dipropionate caused the increase of Arc and Pe nucleus volume, SS neuron volume density, GHRH and SS staining intensity in the ME, when compared with control. Genistein treatment increased: Arc nucleus volume and the volume density of GHRH neurons (by 26%) and SS neurons (1.5 fold), accompanied by higher GHRH and SS staining intensity in the ME, when compared to the orhidectomized group.

DISCUSSION

These results suggest that genistein has a significant effect on hypothalamic region, involved in the regulation of somatotropic system function, and could contribute to the understanding of genistein as substance that alter the hormonal balance.

Soy-based diet exacerbates seizures in mouse models of neurological disease

Seizures are a common phenotype in many neurological disorders including Alzheimer's disease, Down syndrome, and fragile X syndrome. Mouse models of these disorders overexpress amyloid-β protein precursor (AβPP) and amyloid-β (Aβ) and are highly susceptible to audiogenic-induced seizures (AGS). We observed decreased AGS in these mice fed a casein-based, purified diet (D07030301) as opposed to a standard soy protein-containing, non-purified diet (Purina 5015). Our objective in this manuscript was to determine if soy protein, and in particular soy isoflavones, in the Purina 5015 were contributing to the seizure phenotype. Wild running, AGS, and death rates were assessed in juvenile mice fed Purina 5015, D07030301, D07030301 containing soy protein, or D07030301 supplemented with individual isoflavones (750 mg/kg daidzein or genistein). A short treatment (3 days) with Purina 5015 induced wild running and AGS in Alzheimer's disease mice. A 3-day treatment with daidzein-supplemented diet, but not genistein, induced wild running in wild type mice. To understand the mechanism underlying daidzein activity, we assessed dendritic AβPP expression in primary, cultured, wild type neurons treated with daidzein or genistein. In vitro, daidzein significantly increased dendritic AβPP. Thus, the soy isoflavone daidzein recapitulated seizure induction in vivo and altered AβPP expression in vitro. These results have important implications for individuals on soy-based diets as well as for rodent model research.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.

NTP-CERHR expert panel report on the developmental toxicity of soy infant formula

Soy infant formula contains soy protein isolates and is fed to infants as a supplement to or replacement for human milk or cow milk. Soy protein isolates contains estrogenic isoflavones (phytoestrogens) that occur naturally in some legumes, especially soybeans. Phytoestrogens are nonsteroidal, estrogenic compounds. In plants, nearly all phytoestrogens are bound to sugar molecules and these phytoestrogen-sugar complexes are not generally considered hormonally active. Phytoestrogens are found in many food products in addition to soy infant formula, especially soy-based foods such as tofu, soy milk, and in some over-the-counter dietary supplements. Soy infant formula was selected for National Toxicology Program (NTP) evaluation because of (1) the availability of large number of developmental toxicity studies in laboratory animals exposed to the isoflavones found in soy infant formula (namely, genistein) or other soy products, as well as few studies on human infants fed soy infant formula, (2) the availability of information on exposures in infants fed soy infant formula, and (3) public concern for effects on infant or child development. On October 2, 2008 (73 FR 57360), the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR) announced its intention to conduct an updated review of soy infant formula to complete a previous evaluation that was initiated in 2005. Both the current and previous evaluations relied on expert panels to assist the NTP in developing its conclusions on the potential developmental effects associated with the use of soy infant formula, presented in the NTP Brief on Soy Infant Formula. The initial expert panel met on March 15 to 17, 2006, to reach conclusions on the potential developmental and reproductive toxicities of soy infant formula and its predominant isoflavone constituent genistein. The expert panel reports were released for public comment on May 5, 2006 (71 FR 28368). On November 8, 2006 (71 FR 65537), CERHR staff released draft NTP Briefs on Genistein and Soy Formula that provided the NTP's interpretation of the potential for genistein and soy infant formula to cause adverse reproductive and/or developmental effects in exposed humans. However, CERHR did not complete these evaluations, finalize the briefs, or issue NTP Monographs on these substances based on this initial evaluation. Between 2006 and 2009, a substantial number of new publications related to human exposure or reproductive and/or developmental toxicity were published for these substances. Thus, CERHR determined that updated evaluations of genistein and soy infant formula were needed. However, the current evaluation focuses only on soy infant formula and the potential developmental toxicity of its major isoflavone components, e.g. genistein, daidzein (and estrogenic metabolite, equol), and glycitein. This updated evaluation does not include an assessment on the potential reproductive toxicity of genistein following exposures during adulthood as was carried out in the 2006 evaluation. CERHR narrowed the scope of the evaluation because the assessment of reproductive effects of genistein following exposure to adults was not considered relevant to the consideration of soy infant formula use in infants during the 2006 evaluation. To obtain updated information about soy infant formula for the CERHR evaluation, the PubMed (Medline) database was searched from February 2006 to August 2009 with genistein/genistin, daidzein/daidzin, glycitein/glycitin, equol, soy, and other relevant keywords. References were also identified from the bibliographies of published literature. The updated expert panel report represents the efforts of a 14-member panel of government and nongovernment scientists, and was prepared with assistance from NTP staff. The finalized report, released on January 15, 2010 (75 FR 2545), reflects consideration of public comments received on a draft report that was released on October 19, 2009, for public comment and discussions that occurred at a public meeting of the expert panel held December 16 to 18, 2009 (74 FR 53509). The finalized report presents conclusions on (1) the strength of scientific evidence that soy infant formula or its isoflavone constituents are developmental toxicants based on data from in vitro, animal, or human studies; (2) the extent of exposures in infants fed soy infant formula; (3) the assessment of the scientific evidence that adverse developmental health effects may be associated with such exposures; and (4) knowledge gaps that will help establish research and testing priorities to reduce uncertainties and increase confidence in future evaluations. The Expert Panel expressed minimal concern for adverse developmental effects in infants fed soy infant formula. This level of concern represents a "2" on the five-level scale of concern used by the NTP that ranges from negligible concern ("1") to serious concern ("5"). The Expert Panel Report on Soy Infant Formula was considered extensively by NTP staff in preparing the 2010 NTP Brief on Soy Infant Formula, which represents the NTP's opinion on the potential for exposure to soy infant formula to cause adverse developmental effects in humans. The NTP concurred with the expert panel that there is minimal concern for adverse effects on development in infants who consume soy infant formula. This conclusion was based on information about soy infant formula provided in the expert panel report, public comments received during the course of the expert panel evaluation, additional scientific information made available since the expert panel meeting, and peer reviewer critiques of the draft NTP Brief by the NTP Board of Scientific Counselors (BSC) on May 10, 2010 (Meeting materials are available at http://ntp.niehs.nih.gov/go/9741.). The BSC voted in favor of the minimal concern conclusion with 7 yes votes, 3 no votes, and 0 abstentions. One member thought that the conclusion should be negligible concern and two members thought that the level of concern should be higher than minimal concern. The NTP's response to the May 10, 2010 review ("peer-review report") is available on the NTP website at http://ntp.niehs.nih.gov/go/9741. The monograph includes the NTP Brief on Soy Infant Formula as well as the entire final Expert Panel Report on Soy Infant Formula. Public comments received as part of the NTP's evaluation of soy infant formula and other background materials are available at http://cerhr.niehs.nih.gov/evals/index.html.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Dietary genistein and equol (4′, 7 isoflavandiol) reduce oxidative stress and protect rats against focal cerebral ischemia

High soy diets reduce injury in rat models of focal cerebral ischemia and are proposed as alternatives to hormone replacement therapy for postmenopausal women. The present study tests the hypothesis that the major soy isoflavone genistein and the daidzein metabolite equol are neuroprotective in transient focal cerebral ischemia in male and ovariectomized (OVX) female rats by inhibiting oxidative stress. Genistein is the primary circulating soy isoflavone in humans, whereas equol is the primary circulating isoflavone in rats. Male and OVX female Sprague-Dawley rats were fed an isoflavone-reduced diet alone or supplemented with genistein (500 ppm) or equol (250 ppm) for 2 wk prior to 90-min transient middle cerebral artery occlusion followed by reperfusion under isoflurane anesthesia. Indices of oxidative stress were determined 24 h after reperfusion, and cerebral injury was evaluated 3 days after reperfusion. Genistein and equol significantly reduced infarct size in both sexes. Further studies in OVX female rats revealed that this neuroprotection was accompanied by a decrease in NAD(P)H oxidase activity and superoxide levels in the brain. In addition, equol reduced plasma thiobarbituric acid reactive substances, and neurological deficits up to 7 days after injury. There were no significant differences in cerebral blood flow among treatment groups. In conclusion, dietary soy isoflavones are neuroprotective in transient focal cerebral ischemia in male and OVX female rats. These isoflavones may protect the brain via increases in endogenous antioxidant mechanisms and reduced oxidative stress.

Lack of an effect of high dose isoflavones in men with prostate cancer undergoing androgen deprivation therapy

PURPOSE

The profound hypogonadism due to androgen deprivation therapy for prostate cancer results in complications such as sexual dysfunction, poor quality of life, vasomotor symptoms and altered cognition. Since estrogen is associated with cardiovascular risks, phytoestrogens are being increasingly evaluated as a potential treatment for these adverse effects. We evaluated the effects of high dose isoflavones, equivalent to that consumed by Asian populations, on the aforementioned consequences of androgen deprivation therapy.

MATERIALS AND METHODS

A total of 33 men undergoing androgen deprivation therapy for prostate cancer were enrolled in this randomized, double-blind, placebo controlled, 12-week pilot trial. Participants were randomly assigned to receive 20 gm soy protein containing 160 mg total isoflavones (17) vs taste matched placebo, that is 20 gm whole milk protein (16). The study was performed at a tertiary care center in the United States.

RESULTS

At baseline the groups were well matched in demographic parameters, sleep quality, cognition and overall quality of life. However, men in the isoflavone group had a higher baseline prevalence of hot flashes and poor intercourse satisfaction compared to those on placebo. At 12 weeks there were no significant differences between the 2 groups in any outcome measure.

CONCLUSIONS

This pilot study of high dose isoflavones in androgen deprived men showed no significant improvement in cognition, vasomotor symptoms or any other aspect of quality of life measures compared to placebo. Future studies should use variable doses of isoflavones for a longer period before ruling out beneficial isoflavone effects in this population.

Timing of supplementation of selenium and isoflavones determines prostate cancer risk factor reduction in rats

Background

High dietary intake of selenium or isoflavones reduces risk factors for prostate cancer. We tested whether combined supplementation of these two dietary components would reduce prostate cancer risk factors in rats more than supplementation of each component individually.

Methods

Male Noble rat pups were exposed from conception to diets containing an adequate (0.33–0.45 mg/kg diet) or high (3.33–3.45 mg/kg) concentration of selenium as Se-methylselenocysteine and a low (10 mg/kg) or high (600 mg/kg) level of isoflavones in a 2 × 2 factorial design. Pups consumed their respective diets until sacrifice at 35, 100, or 200 days. Male Noble rat breeders, whose exposure to the diets began after puberty, were sacrificed at 336 days. Rats were weighed biweekly. Blood was collected at the time of sacrifice and body fat and prostates were dissected and weighed. Serum levels of leptin, IGF-1, and testosterone were determined using ELISA kits. Serum levels of isoflavones were assayed by GC/MS. Liver activity of selenium-dependent glutathione peroxidase 1 was measured as an indicator of selenium status.

Results

Serum isoflavone concentrations were nearly 100-fold higher at 35 days of age (1187.1 vs. 14.4 ng/mL, mean ± SD) in pups fed the high vs. low isoflavone diets, and remained so at 100 and 200 days, and in breeders. There were no dietary differences in liver glutathione peroxidase activity in pups or breeders. High isoflavone intake significantly (p = 0.001–0.047) reduced body weight in rat pups from 35 days onward, but not in breeders. Body fat and leptin were likewise significantly reduced by high isoflavones in pups while effects in breeders were less pronounced but still significant. High intake of Se and isoflavones each decreased serum IGF-1 in pups at 100 and 200 days, but not in breeders. No consistent dietary effects were observed on serum testosterone or relative weights of prostates. In pups, the combination of high isoflavones and high selenium produced the lowest weight gain, the lowest serum leptin, and the lowest serum IGF-1 concentrations of all four diets.

Conclusion

Combined intake of high selenium and high isoflavones may achieve greater chemopreventive effects than either compound individually. The timing of supplementation may determine the significance of its effects.

Rat models of caloric intake and activity: relationships to animal physiology and human health

Every rodent experiment is based on important parameters concerning the levels of caloric intake and physical activity. In many cases, these decisions are not made consciously, but are based on traditional models. For experimental models directed at the study of caloric intake and activity, the selection of parameters is usually aimed at modeling human conditions, the ultimate goal of which is to gain insight into the pathophysiology of the disease process in man. In each model, it is important to understand the influence of diet, exercise, and genetic background on physiology and the development of disease states. Along the continuum of energy intake from caloric restriction to high-fat feeding, and of energy output from total inactivity to forced exercise, a number of models are used to study different disease states. In this paper, we will evaluate the influence of the quantity and composition of diet and exercise in several animal models, and will discuss how each model can be applied to various human conditions. This review will be limited to traditional models using the rat as the experimental animal, and although it is not an exhaustive list, the models presented are those most commonly represented in the literature. We will also review the mechanisms by which each affects rat physiology, and will compare these to the analogous mechanisms in the modeled human disease state. We hope that the information presented here will help researchers make choices among the available models and will encourage discussion on the interpretation and extrapolation of results obtained from traditional and novel rodent experiments on diet, exercise, and chronic disease.

Regulatory behavior and skin temperature in mid-aged male rats on three different isoflavone-containing diets

Soy isoflavones, the most abundant phytoestrogens, are known as endocrine modulators and appear to be an effective treatment in some women during perimenopause when symptoms such as hot flashes may be reduced. This study examined the effects of dietary soy isoflavones on regulatory behaviors such as body weight, food and water intake, and skin tail temperature by feeding male Long-Evans rats one of the three standard chows (Phyto-free, Phyto-200, and Phyto-600) containing approximately 10-15 ppm, 200 ppm, and 600 ppm of isoflavones, respectively. In an apparent dose-dependent manner, body weight was decreased as a function of increasing isoflavone levels in the diets. The average skin tail temperature of Phyto-600-fed rats (25.5 degrees C) was significantly lower than Phyto-free (27.5 degrees C) values by approximately 2 degrees C. The rats on the Phyto-200 diet (26.6 degrees C) displayed a temperature in between the Phyto-free and Phyto-600 values. Similar to the body weight results, skin tail temperature was decreased in an apparent dose-dependent manner as a function of increasing isoflavone concentrations in the diets. These results suggest that consumption of soy isoflavones alters regulatory behaviors (such as body weight and food and water intake) and skin temperature regulation that may help explain, in part, the beneficial effects of soy isoflavones on obesity and hot flashes in humans.

Effects of chronic exposure to soy meal containing diet or soy derived isoflavones supplement on semen production and reproductive system of male rabbits

Soy and derivative diets deliver large doses of isoflavones to human and animals throughout their lifespan, including gestation. Epidemiologic and experimental data suggest that the consumption of soybean containing foods may protect against cardiovascular disease and decrease breast, prostate and endometrial cancer risk. Based on animal and in vitro studies, however, concerns have been raised that consumption of isoflavones may cause potential adverse effects on the reproductive tract and behavior. The aim of this study was to investigate the effects of chronic consumption of a soy meal containing diet or soy isoflavones supplement on the morphology of reproductive organs, semen quality, age that males reached puberty, and sexual behavior of male rabbits. With this purpose, 16 female rabbits were randomly assigned to receive: (1) a soy- and alfalfa-free diet; (2) a soy- and alfalfa-free diet supplemented with 5mg/kg body wt./day of soy isoflavones; (3) a soy- and alfalfa-free diet supplemented with 20mg/kg body wt./day of soy isoflavones; (4) a diet containing 18% of soy meal, throughout the gestation and lactation. After weaning, male offspring received the same diet, which was given to the respective mother. The age that males reached puberty, semen characteristics and sexual behavior were evaluated in these animals. At 33 weeks of age, the reproductive organs were submitted to histological evaluation. Rabbits, which received large amounts of isoflavones (20mg/kg body wt./day) had a lesser food intake, body weight and semen volume. Spermatogenesis, morphology of male genital organs and sexual behavior did not differ significantly from the control group. We conclude that chronic dietary treatment with soy based diet or soy isoflavones have no adverse effects on the observed reproductive patterns of male rabbits.

AVPV neurons containing estrogen receptor-beta in adult male rats are influenced by soy isoflavones

BACKGROUND

Isoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. It is known that 17beta-estradiol induces apoptosis in anteroventral periventricular nucleus (AVPV) in rat brain. Also, there is evidence that consumption of soy isoflavones reduces the volume of AVPV in male rats. Therefore, in this study, we examined the influence of dietary soy isoflavones on apoptosis in AVPV of 150 day-old male rats fed either a soy isoflavone-free diet (Phyto-free) or a soy isoflavone-rich diet (Phyto-600).

RESULTS

The occurrence of apoptosis in AVPV was examined by TUNEL staining. The incidence of apoptosis was about 10 times higher in the Phyto-600 group (33.1 +/- 1.7%) than in the Phyto-free group (3.6 +/- 1.0%). Furthermore, these apoptotic cells were identified as neurons by dual immunofluorescent staining of GFAP and NeuN as markers of astrocytes and neurons, respectively. Then the dopaminergic neurons in AVPV were detected by immunohistochemistry staining of tyrosine hydroxylase (TH). No significant difference in the number of TH neurons was observed between the diet treatment groups. When estrogen receptor (ER) alpha and beta were examined by immunohistochemistry, we observed a 22% reduction of ERbeta-positive cell numbers in AVPV with consumption of soy isoflavones, whereas no significant change in ERalpha-positive cell numbers was detected. Furthermore, almost all the apoptotic cells were ERbeta-immunoreactive (ir), but not ERalpha-ir. Last, subcutaneous injections of equol (a major isoflavone metabolite) that accounts for approximately 70-90% of the total circulating plasma isoflavone levels did not alter the volume of AVPV in adult male rats.

CONCLUSION

In summary, these findings provide direct evidence that consumption of soy isoflavones, but not the exposure to equol, influences the loss of ERbeta-containing neurons in male AVPV.

Effects of neonatal resveratrol exposure on adult male and female reproductive physiology and behavior

Resveratrol (RES) is a phytoestrogen that has the ability to bind to estrogen receptors (ERs) and evoke biological effects that parallel those exerted by endogenous and synthetic estrogens. We have shown in previous studies that adult female rats acutely exposed to RES exhibit estrous cycle irregularity, ovarian hypertrophy, and alterations in sociosexual behavior. The present experiment characterizes the prolonged effects of maternal RES exposure throughout the lactational period on subsequent behavior, reproductive tissues, and brain morphology of the adult offspring. During adulthood, female offspring exposed to RES throughout nursing exhibited reduced body weight and increased ovarian weight, but exhibited normal estrous cyclicity and sociosexual behavior, without changes in the volume of the sexually dimorphic nucleus of the preoptic area or the anteroventral periventricular nucleus of the hypothalamus. During adulthood, males exposed to RES throughout nursing exhibited decreased body weight and plasma testosterone concentration, increased testicular weight, and reduced sociosexual behavior. These males also had significantly smaller sexually dimorphic nucleus of the preoptic area volumes and larger anteroventral periventricular nucleus volumes compared to male controls. These data suggest that postnatal exposure to RES may affect estrogenic activity in specific peripheral tissues (e.g., the gonads), while inducing antiestrogenic effects in the brain. Thus, the present study supports recent in vitro and in vivo findings that RES differs from most other phytoestrogens by acting as a possible mixed ER agonist/antagonist, depending on the tissue-specific availability of ER subtypes that are preferentially localized in specific brain regions and throughout the reproductive tract. More importantly these data indicate that maternal consumption of phytoestrogens during lactation can have lasting effects on the offspring that may not become apparent until they reach adulthood.

Physiologically-based pharmacokinetic modeling of genistein in rats, Part I: Model development

Genistein is a phytoestrogen-a plant-derived compound that binds to and activates the estrogen receptor-occurring at high levels in soy beans and food products, leading to widespread human exposure. The numerous scientific publications available describing genistein's dosimetry, mechanisms of action, and identified or putative health effects in both experimental animals and humans make it ideal for examination as an example of endocrine-active compound (EAC). We developed a physiologically-based pharmacokinetic (PBPK) model to quantify the internal, target-tissue dosimetry of genistein in adult rats. Complexities of the model include enterohepatic circulation, binding of both genistein and its conjugates to plasma proteins, and the multiple compartments used to describe transport through the bile duct and gastrointestinal tract. Other aspects of the model are simple perfusion-limited transport to the tissue groups and first-order rates of metabolism, uptake, and excretion. We describe here the model structure and initial calibration of the model by fitting to a large data set for Wistar rats. The model structure can be readily extrapolated to describe genistein dosimetry in humans or modified to describe the dosimetry of other phytoestrogens and phenolic EACs. The model does a fair job of capturing the pharmacokinetics. Although it does not describe the interindividual variability and we have not identified a single set of parameters that provide a good fit to the data for both oral and intravenous exposures, we believe it provides a good initial attempt at PBPK modeling for genistein, which can serve as a template for other phytoestrogens and in the design of future experiments and research that can be used to fill data gaps and better estimate model parameters.

Influences of dietary soy isoflavones on metabolism but not nociception and stress hormone responses in ovariectomized female rats

BACKGROUND

Isoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. Few studies have examined the nociception and stress hormone responses after consumption of soy isoflavones.

METHODS

In this study, ovariectomized (OVX) female Long-Evans rats were fed either an isoflavone-rich diet (Phyto-600) or an isoflavone-free diet (Phyto-free). We examined the effects of soy isoflavones on metabolism by measuring body weights, food/water intake, adipose tissue weights as well as serum leptin levels. Also, circulating isoflavone levels were quantified. During chemically induced estrous, nociceptive thresholds were recorded. Then, the animals were subjected to a stressor and stress hormone levels were quantified.

RESULTS

Body weights were significantly lower in Phyto-600 fed rats compared to Phyto-free values within one week and during long-term consumption of soy isoflavones. Correspondingly, Phyto-600 fed animals displayed significantly less adipose deposition and lower serum leptin levels than Phyto-free values. However, rats on the Phyto-600 diet displayed greater food/water intake compared to Phyto-free levels. No changes in thermal pain threshold or stress hormone levels (ACTH and corticosterone) were observed after activation of the hypothalamic-pituitary-adrenal (HPA) stress axis.

CONCLUSION

In summary, these data show that consumption of soy isoflavones 1) increases metabolism, demonstrated by significantly decreased body weights, adipose tissue deposition and leptin levels, but 2) does not alter nociception or stress hormone responses, as indexed by thermal pain threshold, serum corticosterone and ACTH levels in chemically-induced estrous OVX rats.

Behavioral effects of endocrine-disrupting substances: phytoestrogens

A major source of endocrine-disrupting substances, usually not considered in laboratory animal experiments, is the diet used in research investigations. Soy represents the main protein source in almost all natural-ingredient commercially available formulated diets. Soy-derived isoflavones are the most abundant and in many ways the most studied phytoestrogens, and phytoestrogens (isoflavones) are known endocrine disruptors. Research is reviewed that identifies the physiological and behavioral endocrine-disrupting effects of dietary phytoestrogens (isoflavones) in animal diets, including most of the isoflavones, which are in a glycoside form and biologically inactive, and those in the gastrointestinal tract, which are biologically active. The isoflavones genistein and daidzein have similar molecular weights and structural characteristics to that of 17-beta estradiol, which may enable them to exert estrogenic and antiestrogenic properties are described and characterized. Daidzein can be further metabolized to the potent and abundant molecule equol, which in rodents is produced in very large amounts and represents the major circulating metabolite among all biologically active isoflavones. Equol has the unique and important ability to specifically bind 5 alpha-dihydro-testosterone, and to act in turn to inhibit the action of this potent androgen. The specific influence of dietary soy phytoestrogens on consumptive, learning and memory, and anxiety-related behaviors is identified. Regulatory behaviors such as food and water intake, adipose deposition and leptin, and insulin levels affected by dietary isoflavones are also discussed.

Phytoestrogens derived from red clover: an alternative to estrogen replacement therapy?

The benefits of plant extracts from soy and red clover as alternatives to conventional hormone replacement therapy (HRT) have been debated in the past. Here, an attempt has been made to summarize the biochemical and pharmacological data in the light of clinical aspects. Red clover and soy extracts contain isoflavones, which have a high affinity to estrogen receptor alpha (ERalpha), estrogen receptor beta (ERbeta), progesterone receptor (PR) and androgen receptor (AR). The higher affinity to ERbeta compared to ERalpha has been used as an explanation why red clover extracts function as food additives to treat menopausal disorders and may reduce risk of breast cancer. Biochemical analysis shows that these representatives of phytoestrogens have multiple actions beside selective estrogen receptor modulator (SERM)-activity. They act as selective estrogen enzyme modulators (SEEMs), have antioxidant activity and interact with transcription factors such as NF-kappaB. Furthermore, it is indicated that they have protective effects on osteoporosis and the cardiovascular system. Currently 40-50mg of isoflavones (biochanin A, daidzein, formononetin and genistein) are recommended as daily dose. This recommendation is based on the daily intake of phytoestrogens in a traditional Japanese diet.

Effects of dietary phytoestrogens on core body temperature during the estrous cycle and pregnancy

Phytoestrogens have received increased investigative attention due to their potential protective effects in connection to age-related diseases and hormone-dependent cancers. Phytoestrogens appear to be an effective treatment during perimenopause where symptoms, such as hot flashes are reduced. However, little is known about the influence of phytoestrogens on core body temperature during various hormonal conditions. This study examined the effects of dietary phytoestrogens on core body temperature during estrous cycles or pregnancy by feeding Long-Evans rats either a diet rich in phytoestrogens (Phyto-600) versus a diet relatively low in phytoestrogens (Phyto-free). Independent of treatments, body temperature was highest at proestrus and declined during estrus and diestrus. Moreover, the consumption of the Phyto-600 diet moderately decreased body temperature during proestrus, estrus and diestrus versus Phyto-free-fed animals. During pregnancy, independent of treatments, core body temperature decreased as a function of increasing gestational length. Phyto-600-fed rats displayed significantly decreased body temperatures (by approximately 0.5 degrees C) from gestation days 6 to 19, compared to Phyto-free values. The results from this study indicate that consumption of dietary phytoestrogens alters the neuroendocrine mechanism of core body temperature regulation that may help explain, in part, the beneficial effects of phytoestrogens for hot flashes.

Phytoestrogens: hormonal action and brain plasticity

Because of their protective effects in age-related diseases and hormone-dependent cancers, the use of phytoestrogens (isoflavones) as 'natural' remedies has gained prominence. Isoflavones are estrogen mimics that bind estrogen receptors and act like natural selective estrogen receptors modulators. However, limited data exists regarding the influence of soy-derived dietary isoflavones in brain. This brief review will address these topics and examine the influence of dietary isoflavones on sexually dimorphic hypothalamic nuclei. We have observed that altering the isoflavone content within diet significantly affects both the sexually dimorphic nucleus of the preoptic area (a structure that is larger in males than in females) and the anteroventral periventricular nucleus (a structure that is larger in females than in males). Specifically, when animals were switched from phytoestrogen-rich to a phytoestrogen-free diet the volume of the sexually dimorphic nucleus of the preoptic area was decreased in males (no alterations were detected in females). Conversely, when the anteroventral periventricular nucleus was examined, volume changes were recorded in males and females opposite to the patterns observed for the sexually dimorphic nucleus of the preoptic area. Given the practical limitations of examining the effects of dietary phytoestrogens in the human brain, it is important to establish comparative data sets to elucidate phytoestrogen's hormone action and potentially its beneficial brain health effects.

Estrogens and phytoestrogens: brain plasticity of sexually dimorphic brain volumes

Sexually dimorphic brain volumes (sexually dimorphic nucleus of the preoptic area (SDN-POA) and anteroventral periventricular (AVPV) nucleus) are influenced by estrogens. Phytoestrogens, derived from plants (especially soy products), are molecules structurally and functionally similar to estradiol. The purpose of this study was to examine: the consumption of phytoestrogen (using a phytoestrogen-rich (Phyto-600) versus a phytoestrogen-free (Phyto-free)) diets from conception to adulthood (or changing the diets during adulthood) and characterizing (a) circulating plasma phytoestrogen levels, (b) testosterone levels in males, (c) sexually dimorphic brain volumes (i.e. the SDN-POA and AVPV) and (d) the presence of apoptotic cells in these brain structures in Long-Evans rats. Phyto-600 fed animals displayed total serum phytoestrogens levels 37-fold higher compared to Phyto-free values. Circulating testosterone levels were not significantly altered by the diets. Female SDN-POA volumes were not altered by the diets. Whereas, males fed a Phyto-free diet displayed decreased SDN-POA volumes compared to male Phyto-600 values. Females fed the Phyto-600 diet displayed larger AVPV volumes compared to males on the same diet or females on the Phyto-free diet. Males fed the Phyto-free diet had the largest AVPV values compared to Phyto-600 fed males. When the SDN-POA region was examined in lifelong Phyto-free fed males, apoptotic cells were present versus males fed the Phyto-600 diet and in the AVPV region the opposite results were obtained. In summary, consumption of dietary phytoestrogens (estrogen mimics) can alter hormone-sensitive hypothalamic brain volumes in rodents during adulthood.

Time-resolved fluoroimmunoassay for equol in plasma and urine

We present a method for the determination of the isoflavan equol in plasma and urine. This estrogenic isoflavan, which is formed by the action of the intestinal microflora, may have higher biological activity than its precursor daidzein. High urinary excretion of equol has been suggested to be associated with a reduction in breast cancer risk. The method is based on time-resolved fluoroimmunoassay, using a europium chelate as a label. After synthesis of 4'-O-carboxymethylequol the compound is coupled to bovine serum albumin (BSA), then used as antigen to immunize rabbits. The tracer with the europium chelate is synthesized using the same 4'-O-derivative of equol. After enzymatic hydrolysis (urine) or enzymatic hydrolysis and ether extraction (plasma) the immunoassay is carried out. The antiserum cross-reacted to variable extent with some isoflavonoids. For the plasma method the cross-reactivity does not seem to influence the results, which were highly specific. The overestimation of the values using the urine method (164%) compared to the results obtained by a gas chromatography-mass spectrometry (GC-MS) method is probably due to some influence of the matrix on the signal, and interference of structurally related compounds. It is suggested that plasma assays are used but if urine samples are measured a formula has to be used to correct the values making them comparable to the GC-MS results. The correlation coefficients between the time-resolved fluoroimmunoassay (TR-FIA) methods and GC-MS methods were high; r-values for the plasma and urine method, were 0.98 and 0.91, respectively. The intra-assay coefficient of variation (CV%) for the TR-FIA plasma and urine results at three different concentrations vary between 5.5-6.5 and 3.4-6.9, respectively. The inter-assay CV% varies between 5.4-9.7 and 7.4-7.7, respectively. The working ranges of the plasma and urine assay are 1.27-512 and 1.9-512nmol/l, respectively.

Dietary soy phytoestrogens effects on retinal thickness in rats

Naturally occurring estrogen-like molecules in plants (phytoestrogens), present via soy, in animal diets are known to alter brain morphology and reproductive endocrine parameters. This study characterized dietary phytoestrogens' effect on retinal thickness in male and female Long-Evans rats. Experiment 1a and 1b: upon arrival (50 day-old) animals received either a phytoestrogen-rich diet (containing 600 microg phytoestrogen/g diet; referred to as Phyto-600) or a diet low in phytoestrogens (Phyto-free). Males remained on these diets until 140 days of age (females until 160 days of age). In both sexes a significant (but opposite) diet difference in retinal thickness was identified. Male Phyto-600 and female Phyto-free animals had significantly greater retinal thickness compared to Phyto-free males and Phyto-600 females, respectively. Experiment 2: male or female rats were raised from conception on either the Phyto-600 or Phyto-free diet until sacrifice at 75 days of age. Consistent with experiment 1, males exposed to the Phyto-600 diet lifelong had significantly greater retinal thickness than lifelong fed Phyto-free males (no significant differences were identified in females). These data suggest that phytoestrogens influence rat retinal characteristics in a sexually dimorphic manner (more robust effect in males vs. females) and that this influence can occur even in adulthood.

Fitoestrogênios: posicionamento do Departamento de Endocrinologia Feminina da Sociedade Brasileira de Endocrinologia e Metabologia (SBEM)

Para avaliar a utilidade dos fitoestrogênios (FE) na terapia de reposição hormonal da menopausa (TRHM), o Departamento de Endocrinologia Feminina da SBEM reuniu um grupo de especialistas para fazer uma revisão bibliográfica e selecionar trabalhos nos quais a metodologia adotada demonstrasse rigor científico. Os FE têm ações estrogênicas e antiestrogênicas, predominantemente sobre os receptores de estrogênios (E) beta, com potência estrogênica muito inferior à do estradiol. O conteúdo de FE nas suas fontes vegetais é variável, dependendo da forma de cultivo, safra, armazenamento e industrialização. Também a conversão dos precursores em fitormônios ativos no organismo humano tem grande variabilidade individual. A maior parte das pesquisas com FE é realizada in vitro ou com animais de laboratório, nem sempre podendo ser extrapoladas para humanos. Com relação à síndrome do climatério, alguns estudos sugerem discreta melhora dos fogachos, sem modificação do ressecamento vaginal ou das alterações do humor. No metabolismo lipídico, alimentação rica em soja, mas não isoflavonas isoladamente, promove redução do colesterol total, do LDL-col e dos triglicerídeos, mas não elevam o HDL-col, como os E, e podem causar aumento da lipoproteína (a), que os E contribuem para diminuir. Embora alguns estudos de curta duração sugiram aumento da densidade mineral óssea com uso de isoflavonas, não há demonstração de redução de fraturas. Conclui-se que não há evidências convincentes que justifiquem o uso de FE ou alimentação rica em soja como alternativa para a TRHM.

Neurobehavioral effects of dietary soy phytoestrogens

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 concentrations 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 Phyto-free 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.

Visual spatial memory is enhanced in female rats (but inhibited in males) by dietary soy phytoestrogens

BACKGROUND

In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined.

RESULTS

Female rats receiving lifelong exposure to a high-phytoestrogen containing diet (Phyto-600) acquired the maze faster than females fed a phytoestrogen-free diet (Phyto-free); in males the opposite diet effect was identified. In a separate experiment, at 80 days-of-age, animals fed the Phyto-600 diet lifelong either remained on the Phyto-600 or were changed to the Phyto-free diet until 120 days-of-age. Following the diet change Phyto-600 females outperformed females switched to the Phyto-free diet, while in males the opposite diet effect was identified.Furthermore, males fed the Phyto-600 diet had significantly higher phytoestrogen concentrations in a number of brain regions (frontal cortex, amygdala & cerebellum); in frontal cortex, expression of CALB (a neuroprotective calcium-binding protein) decreased while COX-2 (an inducible inflammatory factor prevalent in Alzheimer's disease) increased.

CONCLUSIONS

Results suggest that dietary phytoestrogens significantly sex-reversed the normal sexually dimorphic expression of VSM. Specifically, in tasks requiring the use of reference, but not working, memory, VSM was enhanced in females fed the Phyto-600 diet, whereas, in males VSM was inhibited by the same diet. These findings suggest that dietary soy derived phytoestrogens can influence learning and memory and alter the expression of proteins involved in neural protection and inflammation in rats.