Isoflavones and postmenopausal women: a critical review

Phytoestrogens in postmenopause: the state of the art from a chemical, pharmacological and regulatory perspective

Phytoestrogens represent a diverse group of non-steroidal natural products, which seem to have some oestrogenic effects and are often marketed as food supplements. Population exposed to phytoestrogens is potentially increasing, in part because an unfavourable risk-benefit profile of Hormone Replacement Therapy (HRT) for prolonged treatments (e.g., osteoporosis prevention) highlighted by the publication of the Women Health Initiative (WHI) trial in 2002, but also because many post-menopausal women often perceived phytoestrogens in food supplements as a safer alternative than HRT. Despite of increasing preclinical and clinical studies in the past decade, appealing evidence is still lacking to support the overall positive risk-benefit profile of phytoestrogens. Their status as food supplements seems to discourage studies to obtain new evidence, and the chance to buy them by user's initiative make it difficult to survey their prevalence and pattern of use. The aim of the present review is to: (a) outline the clinical scenario underlying the increased interest on phytoestrogens, by overviewing the evolution of the evidence on HRT and its main therapeutic goals (e.g., menopausal symptoms relief, chemoprevention, osteoporosis prevention); (b) address the chemical and pharmacological features (e.g. chemical structure, botanical sources, mechanism of action) of the main compounds (e.g., isoflavones, lignans, coumestans); (c) describe the clinical evidence on potential therapeutic applications; (d) put available evidence on their riskbenefit profile in a regulatory perspective, in light of the recent regulation on health claims of food supplements.

Reduced mammary tumor progression in a transgenic mouse model fed an isoflavone-poor soy protein concentrate

Dietary exposure to soy has been associated with reduced breast cancer incidence. Soy isoflavones and protein components, such as protease inhibitors and the lunasin peptide, have been indicated as potential agents reducing carcinogenesis. In this study, the effect of soy-based diets was evaluated in a transgenic mouse model of breast carcinoma, overexpressing the neu oncogene. Neu female mice were fed for 20 wk a soy- and isoflavone-free diet (IFD), 4RF21 laboratory mouse diet, soy-based, thus isoflavone-rich (STD), or AIN-76-based semisynthetic diets with a soy protein isolate (SPI) or an isoflavone-poor soy protein concentrate (IPSP) as protein source. Mice were then sacrificed and tumors removed. Mammary tumor weights were not different in SPI versus IFD and STD fed mice. In contrast, mice fed IPSP showed reduced tumor progression versus IFD and STD groups (p < 0.05). Moreover, IPSP fed mice showed lower bromo-2'-deoxyuridine (BrdU) incorporation into breast tumor cells compared to STD and SPI fed animals (p < 0.02). Lung metastases were detected in 80% of IFD fed mice, in 70% of mice fed STD and SPI, and only in 50% of the IPSP fed animals. These results indicate that a diet containing an isoflavone-poor soy protein concentrate may inhibit breast tumor progression and metastasis development.

Dietary genistein negates the inhibitory effect of letrozole on the growth of aromatase-expressing estrogen-dependent human breast cancer cells (MCF-7Ca) in vivo

Genistein (GEN), a soy isoflavone, stimulates growth of estrogen-dependent human tumor cells (MCF-7) in a preclinical mouse model for postmenopausal breast cancer. Antiestrogens and aromatase inhibitors are frontline therapies for estrogen-dependent breast cancer. We have demonstrated that dietary GEN can negate the inhibitory effect of tamoxifen. In this study, we evaluated the interaction of dietary GEN (at 250-1000 p.p.m. in the American Institute of Nutrition 93 growth diet) and an aromatase inhibitor, letrozole (LET), on the growth of tumors in an aromatase-expressing breast cancer xenograft model (MCF-7Ca) in the presence and absence of the substrate androstenedione (AD). Dietary GEN (250 and 500 p.p.m.) or implanted AD stimulated MCF-7Ca tumor growth. Implanted LET inhibited AD-stimulated MCF-7Ca tumor growth. In the presence of AD and LET, dietary GEN (250, 500 and 1000 p.p.m.) reversed the inhibitory effect of LET in a dose-dependent manner. Uterine wet weight, plasma estradiol (E(2)) levels (enzyme-linked immunosorbent assay) and total plasma GEN and LET levels (liquid chromatography-electrospray/tandem mass spectrometry) were measured. Ki-67 (cellular proliferation), aromatase and pS2 protein expression in tumors were evaluated using immunohistochemical (IHC) analysis. In conclusion, dietary GEN increased the growth of MCF-7Ca tumors implanted in ovariectomized mice and could also negate the inhibitory effect of LET on MCF-7Ca tumor growth. These findings are significant because tumors, which express aromatase and synthesize estrogen, are good candidates for aromatase therapy dietary and GEN can reverse the inhibitory effect of LET on tumor growth and adversely impact breast cancer therapy. Caution is warranted for consumption of dietary GEN by postmenopausal women with estrogen-dependent breast cancer taking LET treatment.

Effects of chronic genistein treatment in mammary gland, uterus, and vagina

BACKGROUND

The isoflavone genistein (GEN) is found in soy (Glycine max) and red clover (Trifolium pratense). The estrogenic activity of GEN is known, and it is widely advertised as a phytoestrogen useful in alleviating climacteric complaints and other postmenopausal disorders. Knowledge of effects of long-term administration of GEN in laboratory animals is scarce, and effects in the uterus and mammary gland after long-term administration have not been studied. The uterus and mammary gland are known to be negatively influenced by estrogens used in hormone therapy.

OBJECTIVES

We administered two doses of GEN [mean daily uptake 5.4 (low) or 54 mg/kg (high) body weight (bw)] orally over a period of 3 months to ovariectomized (ovx) rats and compared the effects with a treatment with two doses of 17beta-estradiol [E(2); 0.17 (low) or 0.7 mg/kg bw (high)]. Mammary glands, vaginae, and uteri were investigated morphologically and immunohistochemically. We quantified the expression of proliferating cell nuclear antigen (PCNA) and progesterone receptor (PR) in the mammary gland.

RESULTS

In rats treated with either of the E(2) doses or the high GEN dose, we found increased uterine weight, and histologic analysis showed estrogen-induced features in the uteri. In vaginae, either E(2) dose or GEN high induced hyperplastic epithelium compared with the atrophic controls. In the mammary gland, E(2) (either dose) or GEN increased proliferation and PR expression. Serum levels of luteinizing hormone were decreased by E(2) (both doses) but not by GEN.

CONCLUSIONS

In summary, E(2) and GEN share many effects in the studied organs, particularly in the vagina, uterus, and mammary gland but not in the hypothalamo/pituitary unit.

Menopause: evidence-based practice

Menopause is a physiologic transition and is assuming an increasing importance as the demographic bulge moves through this phase. The transition takes place over several years. It is characterized by depletion of the ovarian follicles, decreasing inhibin leading to increases in follicle-stimulating hormone and loss of the menstrual cycle, accompanied by decreased estradiol production and typical symptoms. The role of hormone therapy in menopause has shifted from preventive use to a limited role in symptom management, for which it remains the most effective intervention. There is good evidence from observational and randomized trials of an increased risk of breast cancer in women on estrogen plus a progestin, compared with those on estrogen alone. There are insufficient data to be able to determine if there are clinically important differences between various progestins and progesterone with respect to breast cancer risk, nor between different regimens. Even relatively short-term exposure to unopposed estrogen will increase the risk of atypical endometrial hyperplasia or cancer; women who have their uterus should be using a progestational agent. Lifestyle changes at menopause are important and effective for preventive health. Recent evidence suggests that the discordance between epidemiologic studies with respect to cardiovascular outcomes and the Women's Health Initiative randomized controlled trial (WHI RCT) data might be attributable in large part to the older age of women enrolled in the WHI.

Effects of isoflavones (soy phyto-estrogens) on serum lipids: a meta-analysis of randomized controlled trials

Objectives

To determine the effects of isoflavones (soy phyto-estrogens) on serum total cholesterol (TC), low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL) and triglyceride (TG).

Methods

We searched electronic databases and included randomized trials with isoflavones interventions in the forms of tablets, isolated soy protein or soy diets. Review Manager 4.2 was used to calculate the pooled risk differences with fixed effects model.

Results

Seventeen studies (21 comparisons) with 853 subjects were included in this meta-analysis. Isoflavones tablets had insignificant effects on serum TC, 0.01 mmol/L (95% CI: -0.17 to 0.18, heterogeneity p = 1.0); LDL, 0.00 mmol/L (95% CI: -0.14 to 0.15, heterogeneity p = 0.9); HDL, 0.01 mmol/L (95% CI: -0.05 to 0.06, heterogeneity p = 1.0); and triglyceride, 0.03 mmol/L (95% CI: -0.06 to 0.12, heterogeneity p = 0.9). Isoflavones interventions in the forms of isolated soy protein (ISP), soy diets or soy protein capsule were heterogeneous to combine.

Conclusions

Isoflavones tablets, isolated or mixtures with up to 150 mg per day, seemed to have no overall statistical and clinical benefits on serum lipids. Isoflavones interventions in the forms of soy proteins may need further investigations to resolve whether synergistic effects are necessary with other soy components.