Effects of dietary isoflavone aglycones on the reproductive tract of male and female mice

Functional hypogonadism among patients with obesity, diabetes, and metabolic syndrome

Testosterone deficiency, defined as low total testosterone combined with physical, cognitive, and sexual signs and/or symptoms, is a common finding in adult men. Functional hypogonadism (FH) is defined as borderline low testosterone (T) secondary to aging and/or comorbid conditions such as diabetes, obesity, and/or metabolic syndrome. The relationship between FH and metabolic disorders is multifactorial and bidirectional, and associated with a disruption of the hypothalamic-pituitary-gonadal axis. Resolution of FH requires the correct diagnosis and treatment of the underlying condition(s) with lifestyle modifications considered first-line therapy. Normalization of T levels through dietary modifications such as caloric restriction and restructuring of macronutrients have recently been explored. Exercise and sleep quality have been associated with T levels, and patients should be encouraged to practice resistance training and sleep seven to nine hours per night. Supplementation with vitamin D and Trigonella foenum-graecum may also be considered when optimizing T levels. Ultimately, treatment of FH requires a multidisciplinary approach and personalized patient care.

Estrogenic Pastures: A Source of Endocrine Disruption in Sheep Reproduction

Phytoestrogens can impact on reproductive health due to their structural similarity to estradiol. Initially identified in sheep consuming estrogenic pasture, phytoestrogens are known to influence reproductive capacity in numerous species. Estrogenic pastures continue to persist in sheep production systems, yet there has been little headway in our understanding of the underlying mechanisms that link phytoestrogens with compromised reproduction in sheep. Here we review the known and postulated actions of phytoestrogens on reproduction, with particular focus on competitive binding with nuclear and non-nuclear estrogen receptors, modifications to the epigenome, and the downstream impacts on normal physiological function. The review examines the evidence that phytoestrogens cause reproductive dysfunction in both the sexes, and that outcomes depend on the developmental period when an individual is exposed to phytoestrogen.

Relevance of the Isoflavone Absorption and Testicular Function: A Systematic Review of Preclinical Evidence

Isoflavone is a phytoestrogen found in different types of food that can act as endocrine disrupters leading to testicular dysfunction. Currently, fragmented data on the action of this compound in the testicles make it difficult to assess its effects to define a safe dose. Thus, we systematically reviewed the preclinical evidence of the impact of isoflavone on testicular function. We also determined which form (aglycones or glycosylated) was the most used, which allowed us to understand the main biological processes involved in testicular function after isoflavone exposure. This systematic review was carried out according to the PRISMA guidelines using a structured search on the biomedical databases MEDLINE (PubMed), Scopus, and Web of Science, recovering and analyzing 22 original studies. The bias analysis and the quality of the studies were assessed by the criteria described in the risk of bias tool developed by SYRCLE (Systematic Review Centre for Laboratory Animal Experimentation). The aglycones and glycosylated isoflavones proved to be harmful to the reproductive health, and the glycosylates at doses of 50, 100, 146, 200, 300, 500, and 600 mg/kg, in addition to 190 and 1000 mg/L, appear to be even more harmful. The main testicular pathologies resulting from the use of isoflavones are associated with Leydig cells resulting from changes in molecular functions and cellular components. The most used isoflavone to evaluate testicular changes was the genistein/daidzein conjugate. The consumption of high doses of isoflavones promotes changes in the functioning of Leydig cells, inducing testicular changes and leading to infertility in murine models.

Leucaena leucocephala extract has estrogenic and antiestrogenic actions on female rat reproduction

Leucaena feed has been reported to cause disruptive effects on livestock reproduction, such as low calving percentages in cows, abortion in female goats and pigs, dead fetuses and fetal resorption in pregnant rats. In this study, the effects of Leucaena on different female reproductive variables were analyzed in two different reproductive conditions: gonadally intact and ovariectomized (OVX) female rats. Leucaena (LEU) was administered to females in both experimental conditions for 30 consecutive days. The effects of the legume extract were compared with those of Daidzein (DAI), a phytoestrogen, and of the female hormone estradiol (E₂). In intact females, LEU disrupted the estrous cycle and female sexual behavior, decreased the number of follicles and corpora lutea, increased uterine and vaginal epithelium in proestrus and diestrus periods, increased uterine and vaginal relative weights during diestrus, and decreased serum progesterone during proestrus. All these effects were similar to those of DAI but lower than E₂-induced effects. In OVX females, LEU decreased body weight, induced lordosis, stimulated vaginal epithelium cornification, increased vaginal weight, and augmented vaginal epithelium thickness. Again, these effects were similar to the effects of DAI and lower than the effects observed with E₂. These results indicate that, in gonadally intact females, LEU can produce antiestrogenic effects in sexual behavior but estrogenic effects on uterine and vaginal weight and epithelia, without modifying serum levels of E₂. In OVX females, in total absence of endogenous E₂, LEU induced estrogenic effects on vaginal weight and epithelia, as well as on sexual behavior.

Effects of Soy in Laboratory Rodent Diets on the Basal, Affective, and Cognitive Behavior of C57BL/6 Mice

Soy is one of the most common sources of protein in many commercial formulas for laboratory rodent diets. Soy contains isoflavones, which are estrogenic. Therefore, soy-containing animal diets might influence estrogen-regulated systems, including basal behavioral domains, as well as affective behavior and cognition. Furthermore, the isoflavone content of soy varies, potentially unpredictably confounding behavioral results. Therefore researchers are increasingly considering completely avoiding dietary soy to circumvent this problem. Several animal studies have investigated the effects of soy free diets but produced inconsistent results. In addition, most of these previous studies were performed in outbred rat or mouse strains. In the current study, we assessed whether a soy-free diet altered locomotion, exploration, nesting, anxiety-related behaviors, learning, and memory in C57BL/6 mice, the most common inbred strain used in biomedical research. The parameters evaluated address measures of basic health, natural behavior, and affective state that also are landmarks for animal welfare. We found minor differences between feeding groups but no indications of altered welfare. We therefore suggest that a soy-free diet can be used as a standard diet to prevent undesirable side effects of isoflavones and to further optimize diet standardization, quality assurance, and ultimately increase the reproducibility of experiments.

Effects of phyto-oestrogen quercetin on productive performance, hormones, reproductive organs and apoptotic genes in laying hens

Quercetin, a polyphenolic flavonoid with diverse biological activities including anti-inflammatory and antiviral, inhibits lipid peroxidation, prevents oxidative injury and cell death. The purpose of the research was to investigate the effect of quercetin on productive performance, reproductive organs, hormones and apoptotic genes in laying hens between 37 and 45 weeks of age, because of the structure and oestrogenic activities similar to 17β-oestradiol. The trial was conducted using 240 Hessian laying hens (37 weeks old), housed in wire cages with two hens in each cage. These hens were randomly allotted to four treatments with six replicates, 10 hens in each replicate and fed with diets containing quercetin as 0, 0.2, 0.4 and 0.6 g/kg feed for 8 weeks. The results showed that dietary quercetin significantly increased (p < .05) the laying rate and was higher in group supplemented with 0.4 g/kg, and feed-egg ratio was decreased (p < .05) by quercetin. Dietary quercetin has no effect (p > .05) on average egg weight and average daily feed intake. Compared with control, secretion of hormones, oestradiol (E₂ )_, progesterone (P4), follicle-stimulating hormone (FSH), luteinizing hormone (LH), insulin-like growth factors-1 (IGF-1) and growth hormone (GH), was found to be significantly higher (p < .05) in quercetin-supplemented groups. Also ovary index, uterus index and oviduct index were not significantly influenced (p > .05) by quercetin, whereas magnum index, isthmus index, magnum length, isthmus length and follicle numbers were significantly increased (p < .05) with quercetin supplementation. Additionally, expression of apoptotic genes was significantly (p < .05) up-regulated or down-regulated by quercetin. These results indicated that quercetin improved productive performance, and its mechanism may be due to the oestrogen-like activities of quercetin.

Equol inhibits growth, induces atresia, and inhibits steroidogenesis of mouse antral follicles in vitro

Equol is a non-steroidal estrogen metabolite produced by microbial conversion of daidzein, a major soy isoflavone, in the gut of some humans and many animal species. Isoflavones and their metabolites can affect endogenous estradiol production, action, and metabolism, potentially influencing ovarian follicle function. However, no studies have examined the effects of equol on intact ovarian antral follicles, which are responsible for sex steroid synthesis and further development into ovulatory follicles. Thus, the present study tested the hypothesis that equol inhibits antral follicle growth, increases follicle atresia, and inhibits steroidogenesis in the adult mouse ovary. To test this hypothesis, antral follicles isolated from adult CD-1 mice were cultured with vehicle control (dimethyl sulfoxide; DMSO) or equol (600 nM, 6 μM, 36 μM, and 100 μM) for 48 and 96 h. Every 24h, follicle diameters were measured to monitor growth. At 48 and 96 h, the culture medium was subjected to measurement of hormone levels, and the cultured follicles were subjected to gene expression analysis. Additionally, follicles were histologically evaluated for signs of atresia after 96 h of culture. The results indicate that equol (100 μM) inhibited follicle growth, altered the mRNA levels of bcl2-associated X protein and B cell leukemia/lymphoma 2, and induced follicle atresia. Further, equol decreased the levels of estradiol, testosterone, androstenedione, and progesterone, and it decreased mRNA levels of cholesterol side-chain cleavage, steroid 17-α-hydroxalase, and aromatase. Collectively, these data indicate that equol inhibits growth, increases atresia, and inhibits steroidogenesis of cultured mouse antral follicles.

Cysteine Prevents Menopausal Syndromes in Ovariectomized Mouse

Cysteine (Cys) is well known to be involved in oxidation-reduction reactions, serving as a source of sulfides in the body. Amino acids are known to improve menopausal symptoms and significantly reduce morbidity. This study aims to find an unrevealed effect of Cys with estrogenic and osteogenic actions. Ovariectomized (OVX) mice were treated with Cys daily for 8 weeks. Estrogen-related and osteoporosis-related factors were analyzed in the vagina, serum, and tibia. Cys was treated in estrogen receptor (ER)-positive human osteoblast-like MG-63 cells and ER-positive human breast cancer Michigan Cancer Foundation-7 (MCF-7) cells. Cysteine administration ameliorated overweightness of the body and vaginal atrophy in the OVX mice. Cysteine increased the levels of alkaline phosphatase (ALP) and 17β-estradiol in the serum of the OVX mice and improved the bone mineral density in the OVX mice. In MG-63 cells, Cys increased the proliferation, ERβ messenger RNA (mRNA) expression, and estrogen response element (ERE) activity. Cysteine increased the ALP activity and the phosphorylation of extracellular signal-regulated kinase. In MCF-7 cells, Cys also increased the proliferation, ERβ mRNA expression, and ERE activity. Taken together, these results demonstrated that Cys has estrogenic and osteogenic activities in OVX mice, MG-63 cells, and MCF-7 cells. The novel insights gained here strongly imply the potential use of Cys as a new agent for postmenopausal women.

Scientific and Regulatory Policy Committee (SRPC) Points to Consider: Histopathology Evaluation of the Pubertal Development and Thyroid Function Assay (OPPTS 890.1450, OPPTS 890.1500) in Rats to Screen for Endocrine Disruptors

The U.S. Environmental Protection Agency Endocrine Disruptor Screening Program (EDSP) is a multitiered approach to determine the potential for environmental chemicals to alter the endocrine system. The Pubertal Development and Thyroid Function in Intact Juvenile/Peripubertal Female and Male Rats (OPPTS 890.1450, 890.1500) are 2 of the 9 EDSP tier 1 test Guidelines, which assess upstream mechanistic pathways along with downstream morphological end points including histological evaluation of the kidneys, thyroid, and select male/female reproductive tissues (ovaries, uterus, testes, and epididymides). These assays are part of a battery of in vivo and in vitro screens used for initial detection of test article endocrine activity. In this Points to Consider article, we describe tissue processing, evaluation, and nomenclature to aid in standardization of assay results across laboratories. Pubertal assay end points addressed include organ weights, estrous cyclicity, clinical pathology, hormonal assays, and histological evaluation. Potential treatment-related findings that may indicate endocrine disruption are reviewed. Additional tissues that may be useful in assessment of endocrine disruption (vagina, mammary glands, and liver) are discussed. This Points to Consider article is intended to provide information for evaluating peripubertal tissues within the context of individual assay end points, the overall pubertal assay, and tier I assays of the EDSP program.

Endogenous and exogenous equol are antiestrogenic in reproductive tissues of apolipoprotein e-null mice

Equol is an isoflavone (IF) metabolite produced by intestinal microbiota in a subset of people consuming dietary soy. Equol producers may show different responses to soy foods and phenotypes related to cancer risk. Here, we assessed the effects of soy IF, endogenous microbial equol production, and dietary racemic equol in a 3 × 2 × 2 factorial experiment using gnotobiotic apoE-null mice (n = 9-11/group/sex). At age 3-6 wk, equol-producing microbiota were introduced to one-half of the colony (n = 122). At age 6 wk, mice were randomized to receive a diet that contained 1 of 3 protein sources: casein and lactalbumin, alcohol-washed soy protein (low IF), and intact soy protein (high IF), with total IF amounts of 0, 42, and 566 mg/kg diet, respectively. One-half of each diet group also received racemic equol (291 mg/kg diet). After 16 wk of dietary treatment, serum isoflavonoid profiles varied with sex, soy IF amount, and intestinal microbiota status. There were no treatment effects on tissues of male mice. In females, reproductive tissue phenotypes differed by equol-producing ability (i.e., microbiota status) but not dietary equol or IF content. Equol producers had lower uterine weight, vaginal epithelial thickness, total uterine area, endometrial area, and endometrial luminal epithelial height compared with nonproducers (P < 0.05 for all), with an association between microbiota status and estrous cycle (P > chi-square = 0.03). Exogenous equol reduced expression of progesterone receptor (PGR) and the proliferation marker Ki67 (P < 0.0001) in vaginal epithelium and endometrium; for endogenous equol, only PGR was reduced (P < 0.0005). Our findings indicate that equol diminishes estrogen-dependent tissue responses in apoE-null mice.

The role of soy isoflavones in menopausal health: report of The North American Menopause Society/Wulf H. Utian Translational Science Symposium in Chicago, IL (October 2010)

OBJECTIVES

If and to what extent soy protein, soy isoflavones, and their metabolites, including S(--)-equol, have beneficial effects on women's health is currently unclear. The North American Menopause Society (NAMS)/Utian Translational Science Symposium on Soy and Soy Isoflavones convened October 9-10, 2010, to clarify basic and clinical research findings as they relate to the risk and benefits of soy products for peri- and postmenopausal women.

METHODS

A working group of faculty and panelists composed of clinical and research experts in the fields of women's health and botanicals met during a 2-day translational symposium to cover the latest evidence-based science on isoflavones as they affect menopausal symptoms, breast and endometrial cancer, atherosclerosis, bone loss, and cognition. Full descriptions of the bioavailability and pharmacokinetics of isoflavones were also presented. Subspecialty groups then broke off with the goal of translating the information into a report for general medical practice and identifying further research areas. All faculty and panelists reviewed the final report, which was then approved by the NAMS Board of Trustees.

RESULTS

From the hundreds of studies reviewed in this report, there are mixed results of the effects on midlife women. Soy-based isoflavones are modestly effective in relieving menopausal symptoms; supplements providing higher proportions of genistein or increased in S(--)-equol may provide more benefits. Soy food consumption is associated with lower risk of breast and endometrial cancer in observational studies. The efficacy of isoflavones on bone has not been proven, and the clinical picture of whether soy has cardiovascular benefits is still evolving. Preliminary findings on cognitive benefit from isoflavone therapy support a "critical window" hypothesis wherein younger postmenopausal women derive more than older women.

CONCLUSIONS

Several areas for further research have been identified on soy and midlife women. More clinical studies are needed that compare outcomes among women whose intestinal bacteria have the ability to convert daidzein to equol (equol producers) with those that lack that ability (equol nonproducers) in order to determine if equol producers derive greater benefits from soy supplementation. Larger studies are needed in younger postmenopausal women, and more research is needed to understand the modes of use of soy isoflavone supplements in women. The interrelations of other dietary components on soy isoflavones consumed as a part of diet or by supplement on equol production also require further study, as do potential interactions with prescription and over-the-counter medications. And finally, greater standardization and documentation of clinical trial data of soy are needed.

Circulating isoflavonoid levels in CD-1 mice: effect of oral versus subcutaneous delivery and frequency of administration

The CD-1 mouse is a commonly used animal model to understand the biological effects of early-life exposure to soy isoflavones in infants. Most studies using CD-1 mice have administered isoflavones by daily subcutaneous injection, while infants receive oral feeds every few hours. The study objectives were to compare the total serum levels of genistein (GEN), daidzein (DAI) and the DAI metabolites equol and O-desmethyl-angolensin (O-DMA), after subcutaneous injection and oral dosing and to determine if frequency of oral administration results in different circulating levels of isoflavones using the CD-1 mouse model. From postnatal days 1 to 5, pups randomly received corn oil or soy isoflavones (total daily dose, 0.010 mg DAI+0.025 mg GEN) by subcutaneous injection once a day, orally once a day or orally every 4 hours. On postnatal day 5, 1 h posttreatment, mice were killed and serum was collected. Mice treated with soy isoflavones had higher (P<.05) serum GEN (female: 1895-3391 ng/ml and male: 483-578 ng/ml) and DAI (female: 850-1580 ng/ml and male: 248-322 ng/ml) concentrations versus control (5-20 ng/ml) mice, regardless of route or frequency of administration, and were similar among dosing strategies. Total serum concentrations of GEN and DAI were higher (P<.05) among females (GEN: 2714 ± 393 ng/ml and DAI: 1205 ± 164 ng/ml) than males (GEN: 521 ± 439 ng/ml and DAI: 288 ± 184 ng/ml) across treatment groups. Serum equol and O-DMA concentrations were negligible (<3 ng/ml) across groups. In conclusion, different routes of delivery and frequency of administration resulted in similar total serum levels of GEN, DAI¸ equol or O-DMA.

The soybean concentrated extract proliferates the vagina of adult rats

OBJECTIVE

The aim of this study was to evaluate changes induced on the vagina of ovariectomized rats after treatment with soybean concentrated extract or conjugated equine estrogens and the association of both drugs.

METHODS

We conducted an experimental study with 50 ovariectomized rats that were randomly divided into five equal groups of 10 animals: GI received vehicle, GII received soybean concentrated extract 46 mg/kg per day, GIII received soybean concentrated extract 120 mg/kg per day, GIV received conjugated equine estrogens 50 μg/kg per day, and GV received conjugated equine estrogens 50 μg/kg and soybean concentrated extract 46 mg/kg per day. The substances were administered by gavage during 21 consecutive days. After that, the animals were killed under anesthesia and the vagina was removed for histological and immunohistochemical analysis. Data were initially submitted to analysis of variance. Whenever a significant difference was detected, the study was complemented with the Tukey-Kramer test for multiple comparisons.

RESULTS

GII did not show any differences on the vaginal epithelium or collagen compared with GI. GIII presented an increase in vaginal epithelium and collagen amount. GIV had the highest amount of collagen and the signals of vaginal proliferation. GV did not show any additional effect compared with GIV.

CONCLUSIONS

Our data suggest that a high dose of isoflavone-rich soy extract may have positive effects on the vaginal structures of ovariectomized rats, but this action is less than that of estrogen treatment on vaginal thickness. In addition, soy extract may not block the estrogen effect on vaginal tissue.

Genistein inhibits osteolytic bone metastasis and enhances bone mineral in nude mice

In this study, the effective activity of genistein on osteolytic bone metastasis and bone mineral was investigated. Female BALB/c-nu/nu mice were injected with estrogen receptor-negative human breast cancer cells, MDA-MB-231, into left cardiac ventricle to form osteolytic bone metastases, and administered genistein subcutaneously after radiologically small but defined osteolytic metastases had been observed (protocol 1), simultaneously with cancer cells inoculation (protocol 2) and prophylactically 7 days before inoculation of cancer cells (protocol 3). In all protocols, genistein (10mg/kg/day) markedly reduced the number and volume of osteolytic bone metastases assessed by radiography and the number of osteoclasts. Furthermore, histomorphometrical analysis revealed that genistein markedly increased trabecular area (Tb.Ar%), trabecular thickness (Tb.Th) and trabecular number (Tb.N), and decreased trabecular separation (Tb.Sp). These results thus demonstrate that genistein could inhibit osteolytic bone metastases, suppress bone resorption, increase bone mass and improve bone microstructure in bone metastases of breast cancer.

Reliability of serum and urinary isoflavone estimates

Sporadic intake and short half-lives of serum or urinary biomarkers may make serum and urinary isoflavones quite unreliable indicators of longer-term dietary soy intake. In 26 participants in the Adventist Health Study-2 (AHS-2) we obtained two measures of fasting morning serum isoflavones, 1-2 years apart. In another 76 subjects we obtained an overnight urine sample and six 24-h dietary recalls over a period encompassing the time of the urine sample. Intraclass correlations (ICC) values for serum isoflavones were 0.11 (log(daidzein)) and 0.28 (log(genistein)). Assuming that the correlation (true dietary intake, true urinary excretion) <0.90, it is shown that this implies an ICC for urinary estimates that exceeds 0.56. As expected, the previous day's soy intake, and its timing, influenced the next morning's serum levels. These results suggest that fasting morning serum isoflavone estimates will provide a poor index of long-term soy intake, but that overnight urinary estimates perform much better.

Soy, phyto-oestrogens and male reproductive function: a review

There is growing interest in the possible health threat posed by the effects of endocrine disruptors on reproduction. Soy and soy-derived products contain isoflavones that mimic the actions of oestrogens and may exert adverse effects on male fertility. The purpose of this review was to examine the evidence regarding the potential detrimental effects of soy and phyto-oestrogens on male reproductive function and fertility in humans and animals. Overall, there are some indications that phyto-oestrogens, alone or in combination with other endocrine disruptors, may alter reproductive hormones, spermatogenesis, sperm capacitation and fertility. However, these results must be interpreted with care, as a result of the paucity of human studies and as numerous reports did not reveal any adverse effects on male reproductive physiology. Further investigation is needed before a firm conclusion can be drawn. In the meantime, caution would suggest that perinatal phyto-oestrogen exposure, such as that found in infants feeding on soy-based formula, should be avoided.

Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men

OBJECTIVE

To determine the effects of consumption of soy protein of varying isoflavone content on parameters of semen quality in healthy young men.

DESIGN

Randomized crossover intervention.

SETTING

University campus.

PATIENT(S)

Healthy adult men (age 27.5 ± 5.67 years, body mass index 25.4 ± 3.14 kg/m(2)).

INTERVENTION(S)

Milk protein isolate (MPI), low-isoflavone soy protein isolate (low-iso SPI; 1.64 ± 0.19 mg isoflavones/day, expressed as aglycone equivalents), and high-isoflavone soy protein isolate (high-iso SPI; 61.7 ± 7.35 mg isoflavones/day, expressed as aglycone equivalents) for 57 days each separated by 28-day washout periods.

MAIN OUTCOME MEASURE(S)

Urinary isoflavones were measured from 24-hour urine samples collected on days 54-56 of each treatment period. Semen quality parameters (semen volume, sperm concentration, sperm count, sperm percent motility, total motile sperm count, sperm morphology) were measured from semen samples collected on days 1 and 57 of each treatment period.

RESULT(S)

Urinary isoflavones were significantly higher after consumption of high-iso SPI compared with the low-iso SPI and MPI. Semen parameters, including semen volume, sperm concentration, sperm count, sperm percent motility, total motile sperm count, and sperm morphology, were not significantly affected by consumption of either low- or high-iso SPI compared with MPI.

CONCLUSION(S)

Consumption of soy protein of low or high isoflavone content does not adversely affect semen quality in a sample of healthy adult men.

Effects of dietary meals containing different levels of phytoestrogens on reproductive function in Bilgoraj ganders

The aim of this study was to investigate how long-term feeding of ganders with diets containing different levels of phytoestrogens affects the morphometry of testes, plasma steroid levels, sperm parameters and reproductive performance. Male Bilgoraj geese were fed diets containing grass meal (with low phytoestrogen levels) and those containing alfalfa meal and soybean meal (with higher levels of phytoestrogens). Testes were obtained from ganders at the peak of mating and the ongoing laying period as well as at the beginning of photorefractoriness. The morphometric parameters were measured in frozen testicular sections. Blood was collected monthly from December to June, and plasma testosterone, androstenedione and corticosterone concentrations were determined. During the mating season, semen was collected and its quantity and quality were investigated. In the flocks (ganders with geese) reproductive output was noted. Seasonal changes were observed in the morphology of testes and in plasma testosterone, androstenedione and corticosterone concentrations in ganders. The feeding of ganders with dietary meals containing higher levels of phytoestrogens did not affect the plasma steroid contents or the majority of the morphometric parameters of testes, except for the height of the seminiferous epithelium, which was lowered. Moreover, diets with higher levels of phytoestrogens decreased the volume of ejaculates and the percentage of normal spermatozoa. However, these changes were not reflected in the fertilisation rates.

Effects of isoflavone supplements vs. soy foods on blood concentrations of genistein and daidzein in adults

The objective of this investigation was to examine the pharmacokinetics of isoflavone concentrations over a 24-h period among healthy adults consuming either soy foods or soy isoflavone tablets at different doses. This randomized, cross-over trial was conducted with 12 generally healthy adults. The three phases of the intervention included isoflavone tablets at (1) 144 mg/day or (2) 288 mg/day and (3) soy foods designed to provide a calculated 96 mg isoflavones/day (doses in aglycone equivalents). Doses were spread out over three meals per day. After 6 days on each study phase, plasma isoflavone concentrations were determined on the seventh day at 0, 4, 8, 10, 12 and 24 h. Average levels of total isoflavone concentrations at 8, 10 and 12 h were >4 micromol/L for the soy food phase and for the higher dose tablet phase. Genistein concentrations were higher overall in the soy food vs. both the lower and the higher dose supplement phases of the study (P<.05). When comparing plasma concentrations for the two doses of tablets, saturation appeared more evident for genistein than for daidzein at the higher dose level. In conclusion, we observed important differences in the pharmacokinetics of genistein and daidzein contrasting the sources and doses of isoflavones when administered three times daily, including a possible advantage for increasing serum concentrations of isoflavones from consuming soy foods relative to isoflavone supplements.

Soy isoflavones, estrogen therapy, and breast cancer risk: analysis and commentary

There has been considerable investigation of the potential for soyfoods to reduce risk of cancer, and in particular cancer of the breast. Most interest in this relationship is because soyfoods are essentially a unique dietary source of isoflavones, compounds which bind to estrogen receptors and exhibit weak estrogen-like effects under certain experimental conditions. In recent years the relationship between soyfoods and breast cancer has become controversial because of concerns – based mostly on in vitro and rodent data – that isoflavones may stimulate the growth of existing estrogen-sensitive breast tumors. This controversy carries considerable public health significance because of the increasing popularity of soyfoods and the commercial availability of isoflavone supplements. In this analysis and commentary we attempt to outline current concerns regarding the estrogen-like effects of isoflavones in the breast focusing primarily on the clinical trial data and place these concerns in the context of recent evidence regarding estrogen therapy use in postmenopausal women. Overall, there is little clinical evidence to suggest that isoflavones will increase breast cancer risk in healthy women or worsen the prognosis of breast cancer patients. Although relatively limited research has been conducted, and the clinical trials often involved small numbers of subjects, there is no evidence that isoflavone intake increases breast tissue density in pre- or postmenopausal women or increases breast cell proliferation in postmenopausal women with or without a history of breast cancer. The epidemiologic data are generally consistent with the clinical data, showing no indication of increased risk. Furthermore, these clinical and epidemiologic data are consistent with what appears to be a low overall breast cancer risk associated with pharmacologic unopposed estrogen exposure in postmenopausal women. While more research is required to definitively allay concerns, the existing data should provide some degree of assurance that isoflavone exposure at levels consistent with historical Asian soyfood intake does not result in adverse stimulatory effects on breast tissue.

Oral antibiotics decrease urinary isoflavonoid excretion in children after soy consumption

How oral antibiotics (OABX) alter isoflavones (IFLs) in soy-consuming children is unknown. We evaluated OABX effects on urinary IFL excretion rates (UIERs) in 17 children, ages 4 to 17 yr, who provided 2 urine collections in pairs of a baseline urine and an overnight urine collection after consuming a body-weight-adjusted dose of soy nuts. The first collection was during OABX treatment for a bacterial infection and the second when healthy and off antibiotics. IFL food levels and UIERs were measured for nonmetabolites (NM), namely, daidzein, genistein (GE), and glycitein, and the metabolites (M) dihydrodaidzein, dihydrogenistein, equol, and O-desmethylangolensin (DMA), by liquid chromatography mass spectrometry. Urinary IFLs were hypothesized to change after OABX due to intestinal microflora alterations. A total of 11 children completed the study correctly. During OABX use, UIER (nmol/h/kg) for GE (6.4 +/- 1.0 vs. 10.1 +/- 1.6), all NM (27.5 +/- 4.8 vs. 36.2 +/- 4.7), and total IFLs (all NM + all M; 29.4 +/- 5.0 vs. 38.8 +/- 4.8) was reduced (P < 0.05) vs. when healthy. In contrast, a trend toward more DMA production during OABX was observed (1.2 +/- 0.6 vs. 0.4 +/- 0.3, P = 0.13). The reduction in urinary IFL appearance could be due to the changes of intestinal bacteria by OABX and/or due to processes related to the infection.

Effect of two types of soy milk and dairy milk on plasma lipids in hypercholesterolemic adults: a randomized trial

OBJECTIVE

To compare the effects of two commercially available soy milks (one made using whole soy beans, the other using soy protein isolate) with low-fat dairy milk on plasma lipid, insulin, and glucose responses.

DESIGN

Randomized clinical trial, cross-over design.

SUBJECTS

Participants were 30-65 years of age, n = 28, with pre-study LDL-cholesterol (LDL-C) concentrations of 160-220 mg/dL, not on lipid lowering medications, and with an overall Framingham risk score of <or=10%.

INTERVENTION

Participants were required to consume sufficient milk to provide 25 g protein/d from each source. The protocol included three 4-week treatment phases, each separated from the next by a wash-out period of >or=4 weeks.

RESULTS

Mean LDL-C concentration at the end of each phase (+/- SD) was 161 +/- 20, 161 +/- 26 and 170 +/- 24 mg/dL for the whole bean soy milk, the soy protein isolate milk, and the dairy milk, respectively (p = 0.9 between soy milks, p = 0.02 for each soy milk vs. dairy milk). No significant differences by type of milk were observed for HDL-cholesterol, triacylglycerols, insulin, or glucose.

CONCLUSION

A 25 g dose of daily soy protein from soy milk led to a modest 5% lowering of LDL-C relative to dairy milk among adults with elevated LDL-C. The effect did not differ by type of soy milk and neither soy milk significantly affected other lipid variables, insulin or glucose.

Inhibition of estrogen action by 2-phenylchromone as AhR agonist in MCF-7 cells

Large amounts of phytoestrogen, a group of estrogen derived from plant sources, are taken from the diet by Asians, but a sign of feminization has not been fully recognized. In this study, we found that some flavonoids inhibited an effect on estrogen action without estrogen receptor (ER) binding. Considering the report that dioxin, an aryl hydrocarbon receptor (AhR) agonist, disrupts the transcriptional activity of ER without binding to the ER, 14 flavonoids were examined for the transcriptional activity of AhR by the yeast reporter assay (AhR). Among them, 2-phenylchromone (flavone, FLA) showed the highest activity. FLA increased the expression of CYP1A1 mRNA, and inhibited the expression of progesterone receptor and pS2 mRNA in MCF-7 cells via non-ER-mediated pathway. Further studies showed that FLA had agonist activity for AhR and enhanced the proteosome-dependent degradation of ERalpha protein. Thus, FLA inhibited the estrogen action without binding to the ER by acting as a competitive agonist for AhR, which meaning that there can be anti-estrogenic flavonoids such as FLA as well as estrogenic ones such as isoflavones.

Isoflavones from soya foods are more bioavailable in children than adults

The purpose of the present study was to determine whether children experience a higher systemic exposure to isoflavonoids when consuming a body weight-adjusted dose of soya compared with adults. Forty study participants were recruited from a local Waldorf school, including twenty-one children and nineteen adults. Participants collected a baseline urine sample and ate immediately thereafter a body weight-adjusted dose of soya nuts (15 g/54.4 kg equivalent to 0.615 (SD 0.036) mg total isoflavones/kg) followed by a 12 h urine collection. Nineteen children and eighteen adults completed the protocol correctly (fourteen child-parent pairs). Children, compared with adults, showed a statistically significant (P < 0.05 by unpaired t test) higher urinary isoflavone excretion rate for daidzein (+39%), genistein (+44%), all non-metabolites (daidzein + genistein + glycitein; +41%) and total isoflavonoids (+32%). Isoflavones are more bioavailable in children v. adults. Urine is an excellent medium to determine systemic isoflavone exposure in children due to its non-invasiveness and high compliance, in particular when collected overnight; it also allows evaluation of completeness of specimen collection.

Bone mass and soy isoflavones in socially housed, premenopausal macaques

BACKGROUND

Soy consumption is associated with a lower incidence of hip fracture in Asian than in Western women, an effect often attributed to estrogen-like compounds (isoflavones) in soy. It is not known whether premenopausal soy exposure initiated in adulthood can increase bone mass and thereby reduce fracture risk.

OBJECTIVE

We aimed to determine whether a high-isoflavone soy diet influences bone mass in soy-naïve, premenopausal cynomolgus monkeys (Macaca fascicularis).

DESIGN

Ninety-four skeletally mature females were randomly assigned to consume diets whose protein content came from either high-isoflavone soy or casein and lactalbumin. Animals were socially housed. Bone mass and circulating isoflavone concentrations were measured at baseline and 19 and 31 mo after the start of treatment; bone biomarkers were measured at baseline and 31 mo.

RESULTS

There were no significant differences at any timepoint in whole-body bone mineral content between casein-fed (112.5 +/- 2.1, 119.2 +/- 1.9, and 120.7 +/- 2.1 g) and soy-fed (117.2 +/- 2.1, 122.4 +/- 2.0, and 125.4 +/- 2.3 g; P=0.12) monkeys. Similar results were seen for spinal bone mineral density (casein-fed: 0.46 +/- 0.01, 0.50 +/- 0.01, and 0.52 +/- 0.01 g/cm(2); soy-fed: 0.47 +/- 0.01, 0.51 +/- 0.01, and 0.52 +/- 0.01 g/cm(2); P=0.30) and bone biomarker measurements-bone-specific alkaline phosphatase (soy-fed: 82.3 +/- 4.1 and 63.2 +/- 3.4 ng/mL; casein-fed: 94.1 +/- 4.5 and 61.7 +/- 4.3 ng/mL; P=0.22) and C-terminal crosslink of type 1 collagen (soy-fed: 0.944 +/- 0.06 and 0.89 +/- 0.08 nmol/L; casein-fed: 0.97 +/- 0.07 and 0.78 +/- 0.06 nmol/L; P=0.20).

CONCLUSION

A soy diet high in isoflavones does not significantly affect bone characteristics in initially soy-naïve premenopausal monkeys.

Estrogenic environmental endocrine-disrupting chemical effects on reproductive neuroendocrine function and dysfunction across the life cycle

Endocrine disrupting chemicals (EDCs) are natural or synthetic compounds that interfere with the normal function of an organism's endocrine system. Many EDCs are resistant to biodegradation, due to their structural stability, and persist in the environment. The focus of this review is on natural and artificial EDCs that act through estrogenic mechanisms to affect reproductive neuroendocrine systems. This endocrine axis comprises the hypothalamic gonadotropin-releasing hormone (GnRH), pituitary gonadotropins, and gonadal steroid hormones, including estrogens. Although it is not surprising that EDCs that mimic or antagonize estrogen receptors may exert actions upon reproductive targets, the mechanisms for these effects are complex and involve all three levels of the hypothalamic-pituitary-gonadal (HPG) system. Nevertheless, considerable evidence links exposure to estrogenic environmental EDCs with neuroendocrine reproductive deficits in wildlife and in humans. The effects of an EDC are variable across the life cycle of an animal, and are particularly potent when exposure occurs during fetal and early postnatal development. As a consequence, abnormal sexual differentiation, disrupted reproductive function, or inappropriate sexual behavior may be detected later in life. This review will cover the effects of two representative classes of estrogenic EDCs, phytoestrogens and polychlorinated biphenyls (PCBs), on neuroendocrine reproductive function, from molecules to behavior, across the vertebrate life cycle. Finally, we identify the gaps of knowledge in this field and suggest future directions for study.

Dietary daidzein and puerarin do not affect pituitary LH expression but exert uterotropic effects in ovariectomized rats

OBJECTIVE

To investigate the potency of LH suppression, as an indirect measure of alleviation of postmenopausal vasomotor symptoms, as well as the uterotropic effects of two isoflavones: daidzein and puerarin in an ovariectomized (ovx) rat model and compare them with the effects of 17beta-estradiol benzoate (E2B).

DESIGN

Eighty female Sprague-Dawley rats were ovx and divided into six different treatment groups and one control group (11-12 animals per group). Daidzein, puerarin and E2B were added to the soy free rodent chow in low and high doses (250 mg and 1000 mg per kg, 600 mg and 3000 mg per kg and 4.3 mg and 17.3 mg per kg, respectively). After 3 months of treatment, animals were sacrificed and using real time RT-PCR, pituitary LHbeta and uterine IGF-1, PR and C3 mRNA levels were measured. Additionally serum LH levels were measured in a radioimmunoassay.

RESULTS

Both of our tested isoflavones at low and high doses had no effect on the expression of the pituitary LH at the mRNA and protein level. Only E2B at both doses significantly decreased pituitary LHbeta gene expression and serum LH levels. Daidzein and puerarin at high dose increased significantly uterine weights. Uterine IGF-1 gene expression was only upregulated in puerarin high group. Uterine PR mRNA levels were higher in animals fed with low dose daidzein and high dose puerarin. Uterine C3 gene expression was upregulated in animals fed with daidzein and puerarin at high doses. Although statistically significant, all these effects were however very discrete compared to those of E2B at low and high doses.

CONCLUSION

We speculate that due to the lack of LH suppressing effects in our model, it is very unlikely for daidzein and puerarin to alleviate vasomotor symptoms in postmenopausal women. In contrast, due to their uterotropic effects, high dose consumption of commercially available preparations containing daidzein or puerarin may expose women with an intact uterus to the risk of endometrial hyperplasia.

Isoflavones in breastfed infants after mothers consume soy

BACKGROUND

The bioavailability of isoflavones in children after soy exposure is uncertain.

OBJECTIVE

We aimed to compare isoflavone patterns in infants exposed to isoflavone-containing breast milk (BF), in tofu-fed (TF) infants, and in mothers consuming a soy beverage.

DESIGN

Eighteen nursing mothers who were not feeding soy foods to their infants consumed one daily serving of a soy protein beverage for 2-4 d and collected their own milk and urine and infant urine. Plasma was collected from infants if venous blood draws were ordered by pediatricians. Blood and urine were collected from additional children after they consumed tofu. Isoflavones were measured by liquid chromatography-mass spectrometry.

RESULTS

In 7 subjects, isoflavone values increased significantly from baseline after mothers ate soy: in maternal urine (x +/- SEM) from 18.4 +/- 13.0 to 135.1 +/- 26.0 nmol/mg creatinine, in breast milk from 5.1 +/- 2.2 to 70.7 +/- 19.2 nmol/L, and in infant urine from 29.8 +/- 11.6 to 111.6 +/- 18.9 nmol/mg creatinine. The mean isoflavone concentration in plasma obtained from 11 BF infants was 19.7 +/- 13.2 nmol/L. TF infants had much higher mean isoflavone values (urine, 229 +/- 129 nmol/mg creatinine; plasma, 1049 +/- 403 nmol/L). Statistically significant correlations were observed between the types of fluids investigated within mothers, between mothers and infants, and within infants. Urinary isoflavone excretion per hour adjusted for dose per body weight was 81% lower for BF infants and 24% higher for TF infants than for their mothers after eating soy.

CONCLUSIONS

More isoflavones appear in children than in adults after adjustment for isoflavone intake. Systemic isoflavone exposure in infants can be determined by urinary analysis.

Urinary isoflavonoid excretion and soy consumption in three generations of Japanese women in Hawaii

OBJECTIVE

To explore soy intake and urinary isoflavonoid excretion within several generations of American-Japanese women based on the hypothesis that earlier generations excrete higher levels of urinary isoflavonoids, in particular the metabolite equol, than later generations.

SUBJECTS

A convenience sample of 43 women from 19 families aged 18-78 years, all of whom reported at least 50% Japanese ancestry.

INTERVENTIONS

Each woman collected overnight urine samples at baseline and after consuming one serving of soymilk, both samples were analyzed for the isoflavonoids daidzein, genistein and equol using liquid chromatography-mass spectrometry.

RESULTS

Median isoflavone intakes during the last year were 7.2 mg/day for the first generation, 7.3 mg/day for the second generation and 6.3 mg/day for the third generation (P=0.36). At baseline, the median isoflavonoid excretion for the first generation was nonsignificantly higher than for later generations (190, 86 and 42 nmol/h; P=0.20) but after intervention, the median urinary isoflavonoid excretion was very similar for the three groups: 2465, 1895 and 2775 nmol/h (P=0.70). Following intervention, a nonsignificantly higher proportion of older than younger women (53 vs 32 and 33%; P=0.41) excreted the metabolite equol. The respective median equol excretion rates by generation following intervention were 39.5, 4.2 and 3.5 nmol/h (P=0.04).

CONCLUSIONS

This small investigation among three generations of Japanese-Americans detected a higher equol production among older women after a soy challenge, but no difference in the excretion of total isoflavonoids after a standardized dose of soymilk was observed.

Dietary soy isoflavones inhibit estrogen effects in the postmenopausal breast

Soy isoflavones are promising dietary agents for prevention of breast cancer. Isoflavones bind estrogen receptors (ER) and may variably act as either estrogen agonists or antagonists depending on the estrogen environment. In this study, we used a postmenopausal primate model to evaluate interactive effects of dietary soy isoflavones and estrogen on risk markers for breast cancer. The experiment followed a randomized factorial design in which 31 ovariectomized adult female cynomolgus monkeys were divided into social groups of three to four animals each and rotated through eight different diets containing the human equivalent of 0, 60, 120, or 240 mg/d soy isoflavones with a dose of oral micronized 17beta-estradiol (E(2)) corresponding to either a low (0.09 mg/d) or a high (0.5 mg/d) postmenopausal estrogen environment. Treatment periods lasted 4 months with a 1-month washout period between diets. The highest isoflavone dose resulted in significantly lower breast proliferation and uterine size in the high-estrogen environment. These effects were accompanied by divergent changes in breast markers of ER activation in which pS2 expression was significantly lower and progesterone receptor expression was significantly higher following the 240 mg isoflavone dose. All isoflavone doses resulted in lower serum estrone and E(2) concentrations in the high-estrogen environment. In contrast, isoflavone treatment had no significant estrogen agonist effects and minimal antagonistic effects in the lower-estrogen environment. These findings show that in the presence of estrogen higher doses of dietary soy isoflavones may alter ER signaling and induce selective antagonistic effects in the breast.

Serum cholesterol efflux potential in postmenopausal women treated with isolated isoflavones

OBJECTIVE

Based on the low cardiovascular risk in Asian populations, phytoestrogens are believed to provide vascular benefits. To elucidate the mechanisms behind the possible cardiovascular effects of phytoestrogens, we evaluated reverse cholesterol transport by assessing the capacity of serum to promote cholesterol efflux in postmenopausal women treated with isolated isoflavones.

DESIGN

Thirty postmenopausal women were treated in a randomized, placebo-controlled, crossover trial with isoflavones or placebo for 3 months interrupted by a 2-month washout period. Serum samples were collected before and after each treatment period, and the cholesterol efflux potential was investigated by using H-cholesterol--labeled Fu5AH cells in culture.

RESULTS

Serum promoted 20.2% +/- 3.0% and 19.9% +/- 3.4% (mean +/- SD) cholesterol efflux after isoflavonoid treatment and after placebo treatment, respectively. Thus, the isoflavone treatment did not affect serum cholesterol efflux. We also studied separately women who produced high concentrations of the isoflavone metabolite equol into serum because some studies suggest that equol could exert favorable vascular effects. However, there was no difference in serum cholesterol efflux capacity between the equol producers (n = 15) and non-equol producers (n = 15).

CONCLUSIONS

In conclusion, isoflavone treatment did not affect serum cholesterol efflux potential in postmenopausal women. Based on our findings, isolated isoflavones do not provide vascular benefits by improving cholesterol efflux.

Soy protein containing isoflavones reduces the size of atherosclerotic plaques without affecting coronary artery reactivity in adult male monkeys

The cardiovascular effects of dietary soy on men or adult male experimental animals have received little attention. We determined the effects of long-term (31 mo) consumption of a commercially available soy protein concentrate containing experimentally varied concentrations of isoflavones on the development of atherosclerosis and vascular reactivity in adult male monkeys. The monkeys were fed atherogenic diets that differed only in the source of protein: Control (n = 30), casein and lactalbumin; low-isoflavone soy (n = 30), a mixture of unmodified soy protein isolate and isoflavone-depleted soy protein isolate containing 0.94 mg of isoflavones/g protein; and high-isoflavone soy (n = 31), unmodified soy protein isolate containing 1.88 mg of isoflavone/g protein. Plasma LDL cholesterol was reduced, whereas HDL cholesterol and apolipoprotein A-1 (P < 0.05) were increased in both groups that consumed soy protein. Atherosclerosis (mean plaque size in the coronary arteries) was reduced by approximately 34% (P < 0.05) in both groups fed soy protein. There were no effects of dietary soy on endothelium-dependent or -independent reactivity of coronary arteries. The results indicate that long-term consumption of soy protein containing a modest amount of isoflavones inhibits the early progression of coronary artery atherosclerosis without affecting endothelium-dependent or -independent arterial function.

Dietary soy protein and isoflavones have no significant effect on bone and a potentially negative effect on the uterus of sexually mature intact Sprague-Dawley female rats

OBJECTIVE

To evaluate the effect of dietary soy protein and isoflavones on bone and the reproductive tract in premenopausal rats.

DESIGN

Three-month-old intact Sprague-Dawley female rats (N = 50) were fed diets containing casein, soy protein, or casein with isoflavone extract for 12 weeks. The amount of casein, soy protein, and extract (per kilogram diet) in each group was: (1) 200 g casein (control); (2) 100 g casein plus 100 g soy protein (low soy); (3) 200 g soy protein (high soy); 4) 200 g casein plus 17.2g extract (low extract); and (5) 200 g casein plus 34.4 g extract (high extract). Diet consumption, body weight, uterine wet weight, urinary deoxypyridinoline concentration, and bone mineral density of the femur and lumbar vertebrae were measured. Femur rigidity was evaluated by histomorphometry. The uterus and vagina were studied histologically.

RESULTS

Rats in all treatment groups had lower body weights and lower deoxypyridinoline concentrations compared with controls, but none of the differences was statistically significant. There was no significant difference in femur and lumbar bone mineral density, uterine wet weights, or histomorphometry between the control and treatment groups. Histologically, uteri and vaginae were normal in all groups except that 1 of 10 rats in the high-soy group and 2 of 10 rats in the high-extract group showed extensive squamous metaplasia in the uterine gland.

CONCLUSION

These results suggest that dietary isolated soy protein and isoflavones have no effect on bone and the vagina during premenopausal period, but may have an adverse effect on the uterus.

Determinants for urinary and plasma isoflavones in humans after soy intake

Consumption of soy foods leads to a biphasic appearance pattern of isoflavones (IFLs) in blood and urine, with peaks appearing at 1-2 h and 4-8 h after intake, but its causes are not understood. IFLs were measured repeatedly from plasma and/or urine after intake of soy foods, IFL glucosides, or aglycons without or with a mildly or radically reduced gut flora as a result of oral antibiotic (AB) treatment, or this combined with mechanical bowel preparation (AB+MBP). The typical biphasic IFL pattern in blood and/or urine was observed when a soy protein drink without (control) or with AB treatment or when IFL glucosides or aglycons were consumed. Soy intake combined with AB+MBP or consumption of puerarin led to a shift of the second peak to much later times. The first peak was absent after puerarin intake. Total urinary IFL recovery was more than 50% lower in the first 24 h, but overall 61% higher after AB+MBP vs. the control. When the area under the curves for corresponding time intervals were compared, individual or total urinary IFL excretion rates were highly correlated with individual or total plasma IFL levels (r=0.85-0.91; P <0.001). At the same urinary excretion rate three times more genistein than daidzein remained in the circulation. We conclude that urinary IFL excretion rates reflect circulating IFL levels, with daidzein appearing less in blood and more in urine than genistein. The first and second IFL peaks are due to uptake in the small and large intestine, respectively. The latter is the major locus of uptake (90%) at usual dietary IFL doses (0.15-1.5 mmol/kg body weight). A reduced gut flora delayed IFL uptake but led overall to increased urinary recovery because of less bacterial degradation in the intestine.