Re: phytoestrogen 한약재의 질병치료 효과..

[문형철]

Br J Pharmacol

. 2016 Oct 20;174(11):1263–1280. doi: 10.1111/bph.13622

The potential health effects of dietary phytoestrogens

Ivonne M C M Rietjens 1,✉, Jochem Louisse 1, Karsten Beekmann 1

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PMCID: PMC5429336  PMID: 27723080

Abstract

Phytoestrogens are plant‐derived dietary compounds with structural similarity to 17‐β‐oestradiol (E2), the primary female sex hormone. This structural similarity to E2 enables phytoestrogens to cause (anti)oestrogenic effects by binding to the oestrogen receptors. The aim of the present review is to present a state‐of‐the‐art overview of the potential health effects of dietary phytoestrogens. Various beneficial health effects have been ascribed to phytoestrogens, such as a lowered risk of menopausal symptoms like hot flushes and osteoporosis, lowered risks of cardiovascular disease, obesity, metabolic syndrome and type 2 diabetes, brain function disorders, breast cancer, prostate cancer, bowel cancer and other cancers. In contrast to these beneficial health claims, the (anti)oestrogenic properties of phytoestrogens have also raised concerns since they might act as endocrine disruptors, indicating a potential to cause adverse health effects. The literature overview presented in this paper illustrates that several potential health benefits of phytoestrogens have been reported but that, given the data on potential adverse health effects, the current evidence on these beneficial health effects is not so obvious that they clearly outweigh the possible health risks. Furthermore, the data currently available are not sufficient to support a more refined (semi) quantitative risk–benefit analysis. This implies that a definite conclusion on possible beneficial health effects of phytoestrogens cannot be made.

초록

식물성 에스트로겐은 식물에서 추출한 식이성 화합물로, 

여성 호르몬의 주성분인 17-β-에스트라디올(E2)과 구조적으로 유사합니다. 

이러한 E2와의 구조적 유사성 덕분에 식물성 에스트로겐은 

에스트로겐 수용체에 결합하여 

(항)에스트로겐 효과를 일으킬 수 있습니다. 

이 글의 목적은 

식이성 식물성 에스트로겐이 건강에 미치는 

잠재적 영향에 대한 최신 정보를 제공하는 것입니다. 

식물성 에스트로겐은 

안면 홍조와 골다공증 같은 갱년기 증상 위험 감소, 심혈관 질환, 비만, 

대사증후군, 제2형 당뇨병 위험 감소, 뇌 기능 장애, 유방암, 전립선암, 대장암, 기타 암과 같은 

다양한 유익한 건강 효과를 가져다준다고 알려져 있습니다. 

이러한 유익한 건강 효과와 달리, 

식물성 에스트로겐의 (항)에스트로겐 특성은 

내분비 교란 물질로 작용하여 건강에 악영향을 미칠 수 있다는 우려를 불러일으켰습니다. 

--> truth reflex

질문 : 위 문장은 옳지 않다 yes

이 논문에서 제시된 문헌 개요는 

식물성 에스트로겐의 잠재적인 건강상의 이점이 여러 가지 보고되었음을 보여줍니다. 

그러나 잠재적인 건강상의 부작용에 대한 데이터를 고려할 때, 이러한 유익한 건강상의 효과에 대한 현재의 증거는 건강상의 위험 가능성을 분명히 능가할 만큼 명확하지 않습니다. 게다가, 현재 이용 가능한 데이터는 보다 세분화된 (반) 정량적 위험-편익 분석을 뒷받침하기에 충분하지 않습니다. 

이것은 식물성 에스트로겐의 건강에 대한 유익한 영향에 대한 명확한 결론을 내릴 수 없다는 것을 의미합니다.

Linked Articles

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc

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AbbreviationsARE/EpRE

antioxidant/electrophile response element

E2

17‐β‐oestradiol

EFSA

European Food Safety Authority

ERα

oestrogen receptor α

ERβ

oestrogen receptor β

ERs

oestrogen receptors (NRA3A)

GPER

G protein‐coupled oestrogen receptor

PPAR

peroxisome proliferator activated receptor (NR1C)

TPO

thyroid peroxidase (EC number 1.11.1.8)

Tables of Links

TARGETS

GPCRs a	Nuclear hormone receptors c
GPER	ERα
Enzymes b	ERβ
AMPK	PPARγ
Thyroid peroxidase (TPO)	PPARa

LIGANDS

17‐β‐oestradiol (E2)

Insulin

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These Tables list key protein targets and ligands in this article which are hyperlinked to corresponding entries in http://www.guidetopharmacology.org, the common portal for data from the IUPHAR/BPS Guide to PHARMACOLOGY (Southan et al., 2016) and are permanently archived in the Concise Guide to PHARMACOLOGY 2015/16 (a,b,cAlexander et al., 2015a,b,c).

Introduction

Phytoestrogens are plant‐derived dietary compounds, found in a wide variety of foods, especially in soy. They represent a diverse group of naturally occurring chemicals with structural similarity to 17‐β‐oestradiol (E2), the primary female sex hormone. Because the lack of phytoestrogens in the diet does not result in deficiency syndromes and because the phytoestrogens do not participate in any essential biological function, phytoestrogens are not considered nutrients. Their structural similarity to E2 enables them to cause (anti)oestrogenic effects by binding to the oestrogen receptors (ERs). This was already noticed in the previous century in Western Australia where sheep grazing on isoflavone‐rich red clover fields showed fertility problems (Bennetts et al., 1946; Stafford, 1997; Scherr et al., 2009). It has been hypothesized that plants use phytoestrogens as part of their natural defence to control female fertility to prevent overpopulation and overgrazing by herbivore animals (Hughes, 1988). In line with this, Setchell (Setchell, 1998) suggested that the fertility problems of zoo animals could be related to the presence of soy isoflavone phytoestrogens in the standard animal diet. Besides these adverse effects, various beneficial health effects have been ascribed to phytoestrogens, such as a lowered risk of menopausal symptoms like hot flushes and osteoporosis. As a result, phytoestrogens are present in a large number of dietary supplements and widely marketed as natural alternatives to oestrogen replacement therapy. In addition, phytoestrogen exposure has been related to lowered risks of cardiovascular disease, obesity, metabolic syndrome and type 2 diabetes, brain function disorders, breast cancer and other forms of cancer including prostate cancer, bowel cancer and other cancers (Hughes, 1988; Adlercreutz, 2002; Bhathena and Velasquez, 2002; Karahalil, 2005; Cederroth and Nef, 2009; Patisaul and Jefferson, 2010; Zhao and Mu, 2011; Jungbauer and Medjakovic, 2014).

In the last decades, soy isoflavones have received attention because of the so called ‘Japanese Phenomenon’ connected to a lower incidence of specific chronic diseases in the Japanese compared with the Western population due to a higher intake of soy foods from early life onwards (Watanabe et al., 2002; Korde et al., 2004; Korde et al., 2009). The fact that the preval‎ence of breast cancer in daughters of migrated Japanese Americans became similar to that of Caucasian Americans after changing their food habits is in line with this observation.

In contrast to these beneficial health claims, the (anti)oestrogenic properties of phytoestrogens have also raised concerns since they might act as endocrine disruptors, indicating a potential to cause adverse health effects. Altogether, the health benefits or risks of isoflavones and other phytoestrogens are still controversial (Wuttke et al., 2007; Andres et al., 2011; Rietjens et al., 2013), and the question of whether phytoestrogens are beneficial or harmful to human health remains unresolved.

Keeping that in mind, the aim of the present review is to present a state‐of‐the‐art overview of the potential health effects of dietary phytoestrogens. The paper presents an overview of the different phytoestrogens present in the diet and food supplements, their supposed mode(s) of action and recent evidence on their supposed beneficial effects.

To obtain an overview of the various health effects, we searched Web of Science, Scopus and PubMed for entries with the search terms ‘phytoestrogen(s)’, ‘review’, ‘meta‐analysis’ and the respective health effects in titles, abstracts and keywords.

소개

식물성 에스트로겐은

식물에서 추출한 식이성 화합물로,

다양한 식품, 특히 콩에서 발견됩니다.

이들은 자연적으로 발생하는 다양한 화학물질 그룹을 대표하며,

17-β-에스트라디올(E2)과 구조적으로 유사합니다.

식이에서 식물성 에스트로겐이 부족해도 결핍 증후군이 발생하지 않고,

식물성 에스트로겐이 필수적인 생물학적 기능에 관여하지 않기 때문에

식물성 에스트로겐은 영양소로 간주되지 않습니다.

그들의 구조적 유사성은 에스트로겐 수용체(ER)에 결합함으로써

에스트로겐(anti)에스트로겐 효과를 유발할 수 있게 합니다.

이것은 지난 세기에 서호주에서 이소플라본이 풍부한 붉은 클로버 밭에서 방목하던 양들이 생식 능력에 문제를 보인 것으로 이미 알려졌습니다(Bennetts et al., 1946; Stafford, 1997; Scherr et al., 2009). 식물들이 식물성 에스트로겐을 자연 방어의 일부로 사용하여 여성 생식력을 조절함으로써 초식 동물에 의한 인구 과잉과 과도한 방목을 방지한다는 가설이 있습니다(Hughes, 1988).

이와 관련하여, Setchell(Setchell, 1998)은 동물원의 동물들의 생식력 문제와 표준 동물 사료에 함유된 콩 이소플라본 식물성 에스트로겐의 존재가 관련이 있을 수 있다고 제안했습니다. 이러한 부작용 외에도 식물성 에스트로겐은 안면 홍조와 골다공증과 같은 갱년기 증상 위험 감소와 같은 다양한 유익한 건강 효과를 가져다준다고 알려져 있습니다.

그 결과, 식물성 에스트로겐은 많은 건강 보조 식품에 함유되어 있으며, 에스트로겐 대체 요법의 자연적인 대안으로 널리 판매되고 있습니다. 또한, 식물성 에스트로겐에 노출되면 심혈관 질환, 비만, 대사 증후군, 제2형 당뇨병, 뇌 기능 장애, 유방암, 전립선암, 대장암, 기타 암을 포함한 기타 형태의 암의 위험이 낮아지는 것으로 나타났습니다(Hughes, 1988년; Adlercreutz, 2002년; Bhathena와 Velasquez, 2002년; Karahalil, 2005년; Cederroth와 Nef, 2009년; Patisaul과 Jefferson, 2010년; Zhao와 Mu, 2011년; Jungbauer와 Medjakovic, 2014년).

지난 수십 년 동안,

일본인의 특정 만성 질환 발병률이 서양인에 비해 낮다는

이른바 '일본인 현상'과 관련하여,

유아기부터 대두 식품 섭취량이 많기 때문에

대두 이소플라본이 주목을 받았습니다(Watanabe et al., 2002; Korde et al., 2004; Korde et al., 2009).

일본계 미국인 이민자의 딸들이 식습관을 바꾼 후

유방암 발병률이 백인 미국인의 발병률과 비슷해진 사실은 이러한 관찰 결과와 일치합니다.

이러한 유익한 건강 효과와 달리, 식물성 에스트로겐의 (항)에스트로겐 특성은 내분비 교란 물질로 작용하여 건강에 악영향을 미칠 수 있다는 우려를 불러일으켰습니다. 이소플라본과 다른 식물성 에스트로겐의 건강상의 이점 또는 위험에 대한 논란은 여전히 진행 중입니다(Wuttke et al., 2007; Andres et al., 2011; Rietjens et al., 2013). 식물성 에스트로겐이 인체 건강에 유익한지 해로운지에 대한 질문은 아직 해결되지 않았습니다.

이를 염두에 두고, 이 리뷰의 목적은 식이성 식물성 에스트로겐이 건강에 미치는 잠재적 영향에 대한 최신 정보를 제공하는 것입니다. 이 논문은 식이성 식물성 에스트로겐과 식품 보조제에 존재하는 다양한 식물성 에스트로겐에 대한 개요, 예상되는 작용 방식, 그리고 예상되는 유익한 효과에 대한 최근의 증거를 제시합니다.

다양한 건강 영향에 대한 개요를 얻기 위해, Web of Science, Scopus, PubMed에서 'phytoestrogen(s)', 'review', 'meta‐analysis'라는 검색어를 제목, 초록, 키워드에 포함하는 항목을 검색했습니다.

Phytoestrogens in the diet

Figure 1 presents an overview of the major types of phytoestrogens known to be present in the diet and food supplements, also including their chemical structure compared with that of E2. The major groups of phytoestrogens present in our diet are isoflavones, prenylflavonoids, coumestans and lignans. The main isoflavones are genistein, daidzein, glycitein, formononetin and biochanin A, which are mainly found in soy, soy‐based food and legumes usually in their conjugated forms like genistin, daidzin, puerarin, glycitin, ononin and sissotrin. In countries in Asia where fermented soy products are part of the traditional diet, isoflavone intake levels may amount to about 15–50 mg isoflavones per day (Eisenbrand et al., 2007). In Western industrial countries, isoflavone intake has been reported to be less than 2 mg isoflavones per day (Eisenbrand et al., 2007), although it may be higher for menopausal women who take soy‐based preparations as an alternative to hormone replacement therapy. The dosages recommended by the manufacturers may vary with the product, and have been reported to amount to values between 20 and 80 mg isoflavones per day (Eisenbrand et al., 2007).

식단에 함유된 식물성 에스트로겐

그림 1은

식단과 식품 보조제에 함유된 것으로 알려진

주요 식물성 에스트로겐의 종류와 E2와 비교한 화학 구조를 보여줍니다.

식단에 함유된 주요 식물성 에스트로겐 그룹은

이소플라본, 프레닐플라보노이드, 쿠메스탄, 리그난입니다.

주요 이소플라본은

제니스테인, 다이제인, 글리시테인, 포르모노네틴, 바이오카닌 A로,

주로 콩과 콩을 기반으로 한 식품과 콩과식물에서 발견되며,

주로 제니스틴, 다이진, 푸에라린, 글리시틴, 오노닌, 시소트린과 같은 결합된 형태로 발견됩니다.

발효된 콩 제품이 전통적인 식단의 일부인 아시아 국가에서는

하루에 약 15-50mg의 이소플라본을 섭취할 수 있습니다(Eisenbrand et al., 2007).

서구 선진국에서는

하루에 2mg 미만의 이소플라본을 섭취하는 것으로 보고되고 있지만(Eisenbrand et al., 2007),

호르몬 대체 요법의 대안으로

콩 기반 제제를 복용하는 폐경기 여성에게는 더 많을 수 있습니다.

제조업체가 권장하는 복용량은 제품에 따라 다를 수 있으며,

하루에 20~80mg의 이소플라본을 섭취하는 것으로 보고되었습니다(Eisenbrand et al., 2007).

Figure 1.

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Chemical structures of E2 and the most common phytoestrogens.

Major prenylflavonoids are 6‐prenylnaringenin, 6‐geranylnaringenin, 8‐prenylnaringenin and isoxanthohumol, which can all be found in hops and beer (Stevens and Page, 2004; Dhooghe et al., 2010). Of the prenylflavonoids, 8‐prenylnaringenin (Figure 1) is the most potent phytoestrogen known. The main coumestans are coumestrol, 4′‐methoxycoumestrol, repensol and trifoliol (Figure 1). Food sources high in coumestans include split peas, pinto beans, lima beans, and especially, alfalfa and clover sprouts. Lignans that are classified as phytoestrogens are enterodiol and enterolactone (Figure 1), which are formed from lignan precursors by intestinal bacteria (Lampe, 2003). Lignan precursors include pinoresinol, lariciresinol, secoisolariciresinol, matairesinol and others (Figure 2). Lignan precursors are found in a wide variety of foods, including flaxseeds, whole grains, fruits and vegetables, sesame seeds and legumes and present a principal source of dietary phytoestrogens in the Western diet (de Kleijn et al., 2002; Valsta et al., 2003).

E2와 가장 일반적인 식물성 에스트로겐의 화학 구조.

주요 프렌닐플라보노이드는

6-프렌닐나링게닌, 6-게라닐나링게닌, 8-프렌닐나링게닌, 이속산토후몰이며,

이 모든 물질은 홉과 맥주에서 발견됩니다(Stevens and Page, 2004; Dhooghe et al., 2010).

프렌닐플라보노이드 중에서

8-프렌닐나링게닌(그림 1)은

알려진 식물성 에스트로겐 중 가장 강력한 에스트로겐입니다.

주요

쿠메스트란은

쿠메스트롤, 4'-메톡시쿠메스트롤, 레펜솔, 트리폴리올(그림 1)입니다.

쿠메스탄이 풍부한 식품에는

쪼개진 완두콩, 핀토 콩, 리마 콩, 그리고 특히 알팔파와 클로버 새싹이 있습니다.

식물성 에스트로겐으로 분류되는 리그난은

장내 세균에 의해 리그난 전구물질에서 형성되는

엔테로디올과 엔테로락톤(그림 1)입니다(Lampe, 2003).

리그난 전구체에는

피노레시놀, 라리시레시놀, 세코이솔라리시레시놀, 마타이레시놀 등이 포함됩니다(그림 2).

pinoresinol, lariciresinol, secoisolariciresinol, matairesinol and others

리그난 전구체는

아마씨, 통곡물, 과일과 채소, 참깨, 콩류 등 다양한 식품에 함유되어 있으며,

서양식 식단에서 식물성 에스트로겐의 주요 공급원입니다(de Kleijn et al., 2002; Valsta et al., 2003).

Figure 2.

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Chemical structures of some dietary lignan precursors.

Mode(s) of action: interaction with oestrogen receptors

The major mode of action by which phytoestogens may exert their possible health effects, is based on their structural similarity to E2 enabling them to cause (anti)oestrogenic effects by binding to the ER. Two main ERs, that is oestrogen receptor α (ERα) (NR3A1) and oestrogen receptor β (ERβ) (NR3A2), have been identified in rats, mice, primates and humans (Kuiper et al., 1996; Ogawa et al., 1998). These ER subtypes have different roles in gene regulation, cancer biology and therapy (Nilsson et al., 2001; Williams et al., 2008; Thomas and Gustafsson, 2011). ERα activation in breast and uterus has been shown to enhance cell proliferation, necessary for growth and tissue maintenance (Pearce and Jordan, 2004; Harris, 2007; Thomas and Gustafsson, 2011) but may also play a role in the unlimited growth of, in particular, ERα‐dependent breast tumours of which around 70% respond to anti‐oestrogen therapy with, for example, the antagonist tamoxifen (Ali and Coombes, 2000). ERβ has been shown to counteract the ERα‐mediated stimulation of cell proliferation (Bardin et al., 2004; Stossi et al., 2004; Strom et al., 2004; Sotoca et al., 2008b; Sotoca et al., 2008a; Thomas and Gustafsson, 2011). These opposite roles of ERα and ERβ in cellular responses to oestrogens have been illustrated by studies using the so‐called T47D–ERβ cell line, a breast cancer cell line with a constant level of ERα, and a tetracycline‐dependent adjustable expression‎ level of ERβ (Strom et al., 2004). When cells of this cell line express mainly ERα, genistein and E2 both appeared to induce a concentration‐dependent increase in proliferation. When ERβ expression‎ is induced, E2 and genistein no longer induce cell proliferation. These results support the conclusion that ERβ plays a role in counteracting ERα‐mediated cell proliferation.

Because ERα and ERβ have different roles in gene regulation, cell proliferation and related health effects, their varying ratio and relative level within tissues may influence the cellular response towards different phytoestrogens. As a result, a certain phytoestrogen may have different effects in, for example, the uterus, in which ERα is the major isoform (Pearce and Jordan, 2004), than in the prostate, in which ERβ is dominant (Enmark et al., 1997; Pearce and Jordan, 2004). These tissue‐specific effects may also result from differences in coactivators and corepressors activated upon activation of the two ERs in different tissues and/or the possible crosstalk of the ERs with other nuclear receptors (Wilson et al., 2004; Chang et al., 2008; Vanden Berghe and Haegeman, 2008; Evers et al., 2014a; Evers et al., 2014b). Furthermore, the actual mode of action of a phytoestrogen, either as an agonist or an antagonist, may also depend on the level of endogenous estrogens present (Barnes et al., 1995).

Using various in vitro models that have been developed for the detection of oestrogen activity, the relative oestrogenic potencies of a variety of phytoestrogens have been quantified. These in vitro assays include receptor binding studies (Kuiper et al., 1998; Gutendorf and Westendorf, 2001; Ikeda et al., 2002; De Angelis et al., 2005; Boue et al., 2011; Park et al., 2012; Djiogue et al., 2014; Liu et al., 2014), ERα and ERβ‐dependent reporter gene assays (Kuiper et al., 1998; Casanova et al., 1999; Dornstauder et al., 2001; Gutendorf and Westendorf, 2001; Ikeda et al., 2002; Rickard et al., 2003; De Angelis et al., 2005; Harris et al., 2005; Escande et al., 2006; ter Veld et al., 2006; Chrzan and Bradford, 2007; Sotoca et al., 2008b; Chu et al., 2009; Kwack et al., 2009; Takeuchi et al., 2009; Boue et al., 2011; Park et al., 2012; Djiogue et al., 2014; Liu et al., 2014; Tiosano et al., 2014; Islam et al., 2015) and cell proliferation assays using oestrogen‐sensitive human cell lines derived from three different female oestrogen‐sensitive tissues, including breast (MCF‐7/BOS and T47D), endometrial (ECC‐1) and ovarian (BG‐1) cells (Wang et al., 2012). Few studies also report on the oestrogenic effects of phytoestrogens in vivo in the so‐called uterotrophic assay (Ding et al., 2010; Wang et al., 2012).

For the present review, we performed a literature research on the binding affinity of E2 and phytoestrogens to ERα and ERβ (expressed as IC50 values from competitive binding assays) and the ERα‐ and ERβ‐mediated gene expression‎ induced by E2 and phytoestrogens (expressed as EC50 values from reporter gene assays). To obtain this overview, we searched Web of Science, Scopus and PubMed for entries with the search terms ‘phytoestrogen(s)’, ‘ERα’, ‘ERβ’, ‘binding affinity’ and/or ‘reporter gene’ in titles, abstracts and keywords. In Figure 3, the reported IC50 and EC50 values for ERα are plotted against the reported IC50 and EC50 values for ERβ. In Tables S1 and S2, the IC50 values and the EC50 values, respectively, and the references to the literature are presented.

작용 방식: 에스트로겐 수용체와의 상호 작용

식물성 에스트로겐이 건강에 미치는 영향을 발휘할 수 있는 주요 작용 방식은

E2와의 구조적 유사성을 바탕으로 하여,

ER에 결합함으로써 (항)에스트로겐 효과를 유발할 수 있도록 하는 것입니다.

쥐, 생쥐, 영장류, 인간에서 두 가지 주요 ER, 즉

에스트로겐 수용체 α(ERα)(NR3A1)와

에스트로겐 수용체 β(ERβ)(NR3A2)가 확인되었습니다(Kuiper et al., 1996; Ogawa et al., 1998).

이 ER 아형은 유전자 조절, 암 생물학 및 치료에서 다른 역할을 합니다(Nilsson et al., 2001; Williams et al., 2008; Thomas and Gustafsson, 2011). 유방과 자궁에서 ERα의 활성화는 성장과 조직 유지에 필요한 세포 증식을 촉진하는 것으로 나타났습니다(Pearce and Jordan, 2004; Harris, 2007; Thomas and Gustafsson, 2011). 그러나 특히 ERα 의존성 유방암의 무제한적인 성장에 영향을 미칠 수 있으며, 이 중 약 70%가 타목시펜(예: 길항제)과 같은 항에스트로겐 요법에 반응합니다(Ali and Coombes, 2000). ERβ는 ERα에 의한 세포 증식 자극을 억제하는 것으로 나타났습니다(Bardin et al., 2004; Stossi et al., 2004; Strom et al., 2004; Sotoca et al., 2008b; Sotoca et al., 2008a; Thomas and Gustafsson, 2011). 에스트로겐에 대한 세포 반응에서 ERα와 ERβ의 이러한 반대되는 역할은 일정한 수준의 ERα를 가진 유방암 세포주인 T47D-ERβ 세포주와 테트라사이클린 의존적 조절 가능한 발현 수준의 ERβ를 사용하는 연구에 의해 설명되었습니다(Strom et al., 2004). 이 세포주의 세포가 주로 ERα를 발현할 때, 제니스테인과 E2는 모두 농도 의존적으로 증식을 유도하는 것으로 나타났습니다. ERβ가 발현되면, E2와 제니스테인은 더 이상 세포 증식을 유도하지 않습니다. 이러한 결과는 ERβ가 ERα에 의한 세포 증식을 억제하는 역할을 한다는 결론을 뒷받침합니다.

ERα와 ERβ는 유전자 조절, 세포 증식, 관련 건강 영향에 있어서 서로 다른 역할을 하기 때문에, 조직 내에서의 다양한 비율과 상대적 수준이 다른 식물성 에스트로겐에 대한 세포 반응에 영향을 미칠 수 있습니다. 결과적으로, 특정 식물성 에스트로겐은 예를 들어, ERα가 주요 이소폼인 자궁(Pearce and Jordan, 2004)과 ERβ가 지배적인 전립선(Enmark et al., 1997; Pearce and Jordan, 2004)에서 다른 효과를 나타낼 수 있습니다. 이러한 조직 특이적 효과는 다른 조직에서 두 개의 ER이 활성화될 때 활성화되는 코액티베이터와 코어프레서의 차이 또는 다른 핵 수용체와의 ER의 교차 간섭으로 인해 발생할 수도 있습니다(Wilson et al., 2004; Chang et al., 2008; Vanden Berghe and Haegeman, 2008; Evers et al., 2014a; Evers et al., 2014b). 또한, 식물성 에스트로겐의 실제 작용 방식은 작용제 또는 길항제로서 존재하는 내인성 에스트로겐의 수준에 따라 달라질 수 있습니다(Barnes et al., 1995).

에스트로겐의 활성을 측정하기 위해 개발된 다양한 체외 모델을 사용하여 다양한 식물성 에스트로겐의 상대적 에스트로겐 활성을 정량화했습니다. 이러한 시험관 내 분석에는 수용체 결합 연구(Kuiper et al., 1998; Gutendorf and Westendorf, 2001; Ikeda et al., 2002; De Angelis et al., 2005; Boue et al., 2011; Park et al., 2012; Djiogue et al., 2014년; Liu 외, 2014년), ERα 및 ERβ 의존성 리포터 유전자 분석(Kuiper 외, 1998년; Casanova 외, 1999년; Dornstauder 외, 2001년; Gutendorf 및 Westendorf, 2001년; Ikeda 외, 2002년; Rickard 외, 2003년; De Angelis 외, 2005년; Harris 외, 2005년; Escande 외, 2006년; ter Veld 외, 2006년; Chrzan과 Bradford, 2007년; Sotoca 외, 2008b; Chu 외, 2009년; Kwack 외, 2009년; Takeuchi 외, 2009년; Boue 외, 2011년; Park 외, 2012년; Djiogue 외, 2014년; Liu 외, 2014년; Tiosano 외, 2014년; Islam 외, 2015년) 그리고 유방(MCF-7/BOS 및 T47D), 자궁 내막(ECC-1) 및 난소(BG-1) 세포를 포함한 세 가지 다른 여성 에스트로겐 민감성 조직에서 유래된 에스트로겐 민감성 인간 세포주를 이용한 세포 증식 분석(Wang et al., 2012). 소위 자궁 영양 작용 분석(Ding et al., 2010; Wang et al., 2012)에서 생체 내 식물성 에스트로겐의 에스트로겐 작용에 대한 연구도 거의 보고되지 않았습니다.

이번 검토를 위해, 우리는 E2와 식물성 에스트로겐이 ERα와 ERβ에 결합하는 친화도(경쟁 결합 분석에서 IC50 값으로 표시)와 E2와 식물성 에스트로겐에 의해 유도된 ERα와 ERβ 매개 유전자 발현(리포터 유전자 분석에서 EC50 값으로 표시)에 대한 문헌 조사를 수행했습니다. 이 개요를 얻기 위해, 웹 오브 사이언스(Web of Science), 스코퍼스(Scopus), 그리고 펍메드(PubMed)에서 제목, 초록, 키워드에 '식물성 에스트로겐(들)', '에스트로겐 수용체(ER)', '에스트로겐 수용체(ER) α', '에스트로겐 수용체(ER) β', '결합 친화도' 및/또는 '보고 유전자'라는 검색어를 포함한 항목을 검색했습니다. 그림 3에서, 에스트로겐 수용체(ER) α에 대한 보고된 IC50 및 EC50 값이 에스트로겐 수용체(ER) β에 대한 보고된 IC50 및 EC50 값에 대해 그래프로 표시되어 있습니다. 표 S1과 S2에는 각각 IC50 값과 EC50 값이 나와 있으며, 문헌에 대한 참고 자료가 제시되어 있습니다.

Figure 3.

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(A) Binding affinities to ERα and ERβ (expressed as IC50 values) and (B) effect concentrations in ERα and ERβ reporter gene assays (expressed as EC50 values) of E2 and phytoestrogens. In Tables S1 and S2, the IC50 and EC50 values, respectively, and the references to the literature are presented.

The overall trend emerging from this overview is that phytoestrogens are less potent oestrogens than E2 with higher IC50 and EC50 values for both receptors (Figure 3). Furthermore, the data show for most phytoestrogens that have been investigated, that the IC50 values are higher for ERα than for ERβ (Figure 3A), indicating a higher binding preference for the ERβ than for the ERα. Only for ferutinine, kievitone and for psoralidin the IC50 values are higher for ERβ than for ERα (Table S1), indicating a higher binding preference for the ERα for these phytoestrogens. A higher preference of ferutinine for ERα was also found in reporter gene studies, whereas for the majority of phytoestrogens tested in reporter gene systems, a preference for ERβ‐mediated gene expression‎ was observed (Figure 3B and Table S2). Most research on the binding of phytoestrogens to ERα and ERβ, and the activation of ERα‐ and ERβ‐mediated gene expression‎ has been conducted with the major soy isoflavones genistein and daidzein (Kuiper et al., 1998; Casanova et al., 1999; Dornstauder et al., 2001; Gutendorf and Westendorf, 2001; Rickard et al., 2003; Bovee et al., 2004; De Angelis et al., 2005; Harris et al., 2005; Escande et al., 2006; Chrzan and Bradford, 2007; Sotoca et al., 2008b; Chu et al., 2009; Takeuchi et al., 2009; Tiosano et al., 2014; Beekmann et al., 2015; Islam et al., 2015). Figure 4 presents an example of such a study with genistein as measured in the human osteosarcoma (U2OS) ERα or ERβ reporter cell lines, comparing the activity of genistein with that of E2 (Sotoca et al., 2008b). The data presented in Figure 4 reveal that for E2, physiological concentrations may be such that only ERα is activated since the EC50 value of E2 for activation of ERα is about 10‐fold lower than that for activation of ERβ. For the isoflavone genistein, the EC50 for ERβ activation is lower than that for ERα activation, indicating that concentrations that activate ERα will at the same time activate ERβ that will counteract the ERα‐mediated effects on cell proliferation (Strom et al., 2004; Sotoca et al., 2008a; Rietjens et al., 2013). This may result in different physiological effects induced by E2 than those induced by phytoestrogens.

이 개요에서 드러나는 전반적인 경향은 식물성 에스트로겐이 E2보다 효능이 낮고, 두 수용체 모두에 대해 IC50 및 EC50 값이 더 높다는 것입니다(그림 3). 또한, 조사된 대부분의 식물성 에스트로겐에 대한 데이터에 따르면, ERα보다 ERβ에 대한 IC50 값이 더 높습니다(그림 3A). 이는 ERβ에 대한 결합 선호도가 ERα보다 더 높음을 나타냅니다. 페루티닌, 키에비톤, 그리고 소랄리딘의 경우, ERα보다 ERβ에 대한 IC50 값이 더 높습니다(표 S1). 이는 이들 식물성 에스트로겐이 ERα에 더 많이 결합한다는 것을 의미합니다. ERα에 대한 페루티닌의 선호도가 더 높은 것도 리포터 유전자 연구에서 발견되었으며, 리포터 유전자 시스템에서 테스트된 대부분의 식물성 에스트로겐의 경우 ERβ 매개 유전자 발현에 대한 선호도가 관찰되었습니다(그림 3B 및 표 S2).

식물성 에스트로겐과 ERα 및 ERβ의 결합, 그리고 ERα 및 ERβ 매개 유전자 발현의 활성화에 대한 대부분의 연구는 주요 콩 이소플라본인 제니스테인(genistein)과 다이제인(daidzein)을 대상으로 수행되었습니다(Kuiper et al., 1998; Casanova et al., 1999; Dornstauder et al., 2001; Gutendorf and Westendorf, 2001년; Rickard 외, 2003년; Bovee 외, 2004년; De Angelis 외, 2005년; Harris 외, 2005년; Escande 외, 2006년; Chrzan과 Bradford, 2007년; Sotoca 외, 2008b; Chu 외, 2009년; Takeuchi 외, 2009년; Tiosano 외, 2014년; Beekmann 외, 2015년; Islam 외, 2015년). 그림 4는 인간 골육종(U2OS) ERα 또는 ERβ 리포터 세포주에서 측정된 제니스테인 연구의 예를 보여줍니다. 이 그림은 제니스테인의 활성을 E2의 활성과 비교합니다(Sotoca et al., 2008b). 그림 4에 제시된 데이터는 E2의 경우, ERα의 활성화에 대한 E2의 EC50 값이 ERβ의 활성화에 대한 값보다 약 10배 낮기 때문에 생리학적 농도가 ERα만 활성화될 수 있는 수준일 수 있음을 보여줍니다. 이소플라본 제니스테인(genistein)의 경우, ERβ 활성화에 대한 EC50이 ERα 활성화에 대한 EC50보다 낮습니다. 이는 ERα를 활성화하는 농도가 동시에 ERβ를 활성화하여 ERα가 세포 증식에 미치는 영향을 상쇄한다는 것을 의미합니다(Strom et al., 2004; Sotoca et al., 2008a; Rietjens et al., 2013). 이로 인해 E2에 의해 유발되는 생리적 효과와 식물성 에스트로겐에 의해 유발되는 생리적 효과가 달라질 수 있습니다.

Figure 4.

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Induction of oestrogen responsive element mediated luciferase activity in the ERα‐ and ERβ‐containing U2OS reporter cell lines by (A) E2 and (B) genistein. For further details, see Rietjens et al. (2013).

It is also of interest to note the possible role of G protein‐coupled oestrogen receptors (GPERs), since many of the phytoestrogens including the soy isoflavone genistein and possibly equol activate GPERs (Prossnitz and Barton, 2011). In cell lines of thyroid, ovarian, endometrial and breast cancers, stimulation of GPERs with oestrogens including genistein, activates a signalling pathway that promotes proliferation, although inhibition of proliferation has also been reported. In particular, genistein has been reported to stimulate growth of MCF‐7 cells through a GPER‐dependent mechanism (Prossnitz and Barton, 2011).

또한, 대두 이소플라본인 제니스테인(genistein)과 에쿠올(equol)을 포함한 많은 식물성 에스트로겐이 GPERs를 활성화시키기 때문에, G 단백질 결합 에스트로겐 수용체(G protein‐coupled oestrogen receptors, GPERs)의 가능한 역할에 주목하는 것도 흥미롭습니다(Prossnitz and Barton, 2011). 갑상선, 난소, 자궁 내막 및 유방암의 세포주에서 제니스테인(genistein)을 포함한 에스트로겐으로 GPER을 자극하면 증식을 촉진하는 신호 전달 경로를 활성화하지만, 증식 억제도 보고되었습니다. 특히 제니스테인은 GPER 의존적 메커니즘을 통해 MCF-7 세포의 성장을 촉진하는 것으로 보고되었습니다(Prossnitz and Barton, 2011).

Mode(s) of action: epigenetic effects

Another mode of action underlying the health effects of phytoestrogens may relate to epigenetic mechanisms. Various natural bioactive compounds have been shown to affect the epigenome, but for phytoestrogens, this has been mainly assessed for the soy isoflavone genistein, and to a lesser extent for the soy isoflavone daidzein and its microbial metabolite equol (Remely et al., 2015b). Especially for the reduction in cancer risk by the isoflavone genistein, a role for epigenetic changes resulting in alterations in the expression‎ of genes that regulate cell proliferation and differentiation has been reported (Dolinoy et al., 2006; Hilakivi‐Clarke et al., 2010). Genistein consumption is also among the factors that have been associated with epigenetic modifications in obesity (Remely et al., 2015a). Among these epigenetic changes were effects on DNA methylation, histone modification and microRNA regulation (Rietjens et al., 2013). Several studies have assessed the effects of genistein on DNA methylation.

Dolinoy et al. (2006) investigated, in the so‐called agouti mouse model, the effect of genistein on DNA methylation in the offspring exposed during gestation. Genistein induced CpG hypermethylation of six CpG sites upstream of the agouti gene, resulting in a shift of the coat colour distribution towards pseudoagouti (brown), and a decrease in the incidence of the onset of obesity in the offspring at adult age (Dolinoy et al., 2006). The authors speculated that this ability of genistein to increase DNA methylation might provide an explanation for the lower incidence of certain cancers in Asians as compared with Westerners (Qin et al., 2009). This observation could provide another explanation for the different outcomes reported when studying effects of phytoestrogens on breast cancer incidence. It could be that beneficial effects result from epigenetic modifications that occur early in life perhaps even through soy intake by the mother, but that these beneficial effects may not be observed when intake of soy isoflavones starts later in life, for example when using hormone replacement therapy. Also, adolescence may reflect a sensitive period for phytoestrogens, and phytoestrogen intake during adolescence may reduce breast cancer risk later in life (Lee et al., 2009; Anderson et al., 2013; Molzberger et al., 2013).

In in vitro studies, genistein has been shown to decrease the methylation of several tumour suppressor genes (Pudenz et al., 2014), which may be mediated by the inhibition of DNA methyl transferase (DNMT) activity (Singh et al., 2013). This may allow silenced tumour suppressor genes to be re‐expressed, indicating a potential beneficial effect of genistein. However, inhibition of DNMT may also lead to a reduced methylation of proto‐oncogenes, as has been shown for coumestrol, daidzein and equol (Lyn‐Cook et al., 1995; Koo et al., 2015), which may indicate a possible adverse effect. However, whether these findings from in vitro studies are relevant for the in vivo situation remains to be established, since genistein has been shown to cause an increase in DNA methylation upon exposure in vivo, such as in the agouti mouse model as mentioned above (Dolinoy et al., 2006) and in humans (Qin et al., 2009). This human study was a double‐blind, randomized trial with 34 healthy premenopausal women, who received 40 or 140 mg isoflavones (including genistein, daidzein and glycitein) a day for the duration of one menstrual cycle, followed by characterization of the methylation status of five cancer related genes known to be methylated in breast cancer (p16, RASSF1A, RARβ2, ER and CCND2) assessed in isolated breast tissue samples (Qin et al., 2009). The results obtained revealed a treatment‐related hypermethylation of the tumour suppressor genes RARβ2 and CCND2. The implications of these findings for human health are not clear yet, although this increase in methylation of tumour suppressor genes may indicate a possible adverse epigenetic change.

작용 방식: 후성유전학적 효과

식물성 에스트로겐의 건강 효과에 기초한 또 다른 작용 방식은

후성유전학적 메커니즘과 관련이 있을 수 있습니다.

다양한 천연 생체 활성 화합물이

후성유전체에 영향을 미치는 것으로 나타났지만,

식물성 에스트로겐의 경우 주로 대두 이소플라본 제니스테인, 그리고 그보다 적은 정도이지만

대두 이소플라본 다이제인과 그 미생물 대사 산물인 에쿠올에 대한 평가가 이루어졌습니다(Remely et al., 2015b).

특히

이소플라본 제니스테인(genistein)에 의한 암 위험 감소와 관련하여,

세포 증식과 분화를 조절하는 유전자의 발현을 변화시키는

후성적 변화의 역할이 보고되었습니다(Dolinoy et al., 2006; Hilakivi‐Clarke et al., 2010).

제니스테인 섭취는

비만과 관련된 후성유전적 변형과도 관련이 있는 요인 중 하나입니다(Remely et al., 2015a).

이러한 후성유전적 변화 중에는

DNA 메틸화, 히스톤 변형, 마이크로RNA 조절에 대한 영향이 있습니다(Rietjens et al., 2013).

여러 연구에서 제니스테인이 DNA 메틸화에 미치는 영향을 평가했습니다.

Dolinoy et al. (2006)은 소위 아구티 마우스 모델에서 임신 기간 동안 노출된 자손의 DNA 메틸화에 대한 제니스테인의 영향을 조사했습니다. 제니스테인(Genistein)은 아구티(agouti) 유전자 상류에 있는 6개의 CpG 부위의 CpG 과메틸화를 유도하여 털색 분포가 슈도아구티(갈색) 쪽으로 이동하고, 성인기에 비만이 되는 자손의 발생률이 감소하는 결과를 가져왔습니다(Dolinoy et al., 2006). 저자들은 제니스테인이 DNA 메틸화를 증가시키는 능력이 서양인에 비해 아시아인의 특정 암 발병률이 낮은 이유를 설명할 수 있을 것이라고 추측했습니다(Qin et al., 2009). 이 관찰은 유방암 발병률에 대한 식물성 에스트로겐의 영향을 연구할 때 보고된 다른 결과들에 대한 또 다른 설명을 제공할 수 있습니다. 어쩌면 어머니가 콩을 섭취함으로써 일찍부터 생기는 후성유전학적 변화로 인해 유익한 효과가 나타날 수 있지만, 호르몬 대체 요법을 사용하는 등 콩 이소플라본을 섭취하는 시기가 늦어지면 이러한 유익한 효과가 관찰되지 않을 수 있습니다. 또한, 청소년기는 식물성 에스트로겐에 민감한 시기일 수 있으며, 청소년기에 식물성 에스트로겐을 섭취하면 나중에 유방암에 걸릴 위험이 줄어들 수 있습니다(Lee et al., 2009; Anderson et al., 2013; Molzberger et al., 2013).

체외 연구에서 제니스테인은 여러 종양 억제 유전자의 메틸화를 감소시키는 것으로 나타났습니다(Pudenz et al., 2014). 이는 DNA 메틸 전이 효소(DNMT) 활성의 억제에 의해 매개될 수 있습니다(Singh et al., 2013). 이것은 침묵된 종양 억제 유전자가 재발현될 수 있도록 해줌으로써 제니스테인의 잠재적인 유익한 효과를 나타낼 수 있습니다. 그러나 DNMT의 억제는 쿠메스트롤, 다이제인, 에쿠올(Lyn-Cook et al., 1995; Koo et al., 2015)에서 나타난 것처럼 원발성 종양 유전자의 메틸화를 감소시킬 수 있으며, 이는 부작용을 나타낼 수 있음을 의미합니다. 그러나, 위에서 언급한 아구티 마우스 모델(Dolinoy et al., 2006)과 인간(Qin et al., 2009)과 같이 생체 내 노출 시 제니스테인이 DNA 메틸화를 증가시키는 것으로 나타났기 때문에, 이러한 시험관 내 연구 결과가 생체 내 상황과 관련이 있는지는 아직 밝혀지지 않았습니다. 이 인간 대상 연구는 34명의 건강한 폐경 전 여성을 대상으로 한 이중 맹검 무작위 시험으로, 이들은 40mg 또는 140mg의 이소플라본(제니스테인, 다이제인, 글리시테인 포함)을 투여받았습니다. 한 생리 주기의 하루 동안, 유방암에서 메틸화되는 것으로 알려진 5가지 암 관련 유전자(p16, RASSF1A, RARβ2, ER, CCND2)의 메틸화 상태를 분리된 유방 조직 샘플에서 평가합니다(Qin et al., 2009). 그 결과, 종양 억제 유전자인 RARβ2와 CCND2의 치료 관련 과메틸화가 나타났습니다. 종양 억제 유전자의 메틸화가 증가하는 것은 역설적으로 후성유전학적 변화가 일어날 가능성이 있음을 의미할 수 있지만, 이러한 결과가 인간의 건강에 미치는 영향은 아직 명확하지 않습니다

.

Other possible modes of action

In addition to the action of phytoestrogens via the oestrogen receptors or epigenetic modes of action, some studies suggested other possible modes of action of phytoestrogens. This includes, for example, the effects of genistein resulting in activation of AMP‐activated protein kinase (EC number 2.7.11.31) in cells exposed to genistein in vitro (Hwang et al., 2005; Park et al., 2010). The exact mechanism underlying this activation has not been fully elucidated (Hsu et al., 2011) but may be related to genistein‐mediated stimulation of intracellular production of ROS (Hwang et al., 2005).

Another mode of action may relate to the action of phytoestrogens as kinase inhibitors (Dubey et al., 1999; Kang et al., 2007; Yan et al., 2010). Given that the human kinome is composed of hundreds of protein kinases of which many have been reported to be disease associated (Manning et al., 2002; Lahiry et al., 2010), one could suggest that this is a possible mode of action underlying the effects of phytoestrogens on health. It is important to note, however, that EC50 values generally reported for this inhibition of protein kinases by isoflavones seem to be around the two‐digit and lower three‐digit μM range (Dubey et al., 1999; Kang et al., 2007; Kim et al., 2009), which is substantially higher than generally reported physiological plasma concentrations of the respective phytoestrogens, which tend to be in the two‐ to three‐digit nM range, rarely reaching low μM concentrations (King and Bursill, 1998; Verkasalo et al., 2001; Setchell et al., 2003).

Phytoestrogens may also activate the PPAR (NRC1C) family including, particularly PPARα (NR1C1), and PPARγ (peroxisome proliferator activated receptor γ) (NR1C3) (Jungbauer and Medjakovic, 2014). It has been suggested that this mode of action mainly contributes to the possible effects of phytoestrogens on obesity, metabolic syndrome and type 2 diabetes, as PPARγ agonists are effective drugs for patients with type 2 diabetes. Specifically, isoflavones and their metabolites appear to be PPAR agonists with EC50 values in the two‐digit μM range (Jungbauer and Medjakovic, 2014). It remains to be established whether physiological concentrations are actually high enough to induce these PPAR‐mediated effects.

Another mode of action, suggested mainly for the beneficial health effects of phytoestrogens, is the induction of antioxidant/electrophile response element (ARE/EpRE)‐mediated gene expression‎ by activation of nuclear factor erythroid 2‐related factor 2‐Keap 1 signalling (Jungbauer and Medjakovic, 2014). EpRE‐mediated induction of gene expression‎ leads to increased cellular defence against the toxicity of electrophiles and ROS and related adverse health effects. Activation of this pathway may be related to protection against tumour induction and oxidative stress in cardiovascular disease.

Finally, it is of interest to consider the possible role of polymorphisms in the differential effects of phytoestrogens. So far, differences in health effects of phytoestrogens have not been related to specific gene polymorphisms. However, since ERs seem to play an important role in several of the health effects of phytoestrogens, it can be expected that phytoestrogen‐related health effects may differ between persons with differences in ER function, for example resulting from ER gene polymorphisms. Nott et al. (2008) concluded that an increasing body of evidence implicates ERα polymorphisms as one of the contributing factors for differential responses to oestrogen competitors and that polymorphisms in the ER genes may influence the individual response to hormone replacement therapy (Gennari et al., 2005). Polymorphisms of genes that play a role in the metabolism of (phyto)oestrogens may also play a role in differences in health effects of phytoestrogens in the human population (Wang et al., 2011). Also, polymorphisms related to interindividual differences in the gut microbiota and the consequences of these differences for formation of (in)active metabolites may play a role. An adequate example is the formation of equol as a metabolite of daidzein only in a part of the population. Equol has been reported to be more active as an oestrogen‐active compound than daidzein itself (Magee, 2011). Another example is the formation of enterodiol and enterolactone from ingested lignans through the gut microbiota in only a part of the population (Kuijsten et al., 2005; Hullar et al., 2015). Also, these differences can be an underlying reason for different responses to phytoestrogen exposure in the population.

Effects of phytoestrogens on menopausal symptoms

Several meta‐analyses investigated the effects of phytoestrogens or soy isoflavone extracts or supplements on menopausal symptoms. These studies reported not only a reduction in the frequency and severity of hot flashes (Howes et al., 2006; Taku et al., 2012; Chen et al., 2015) but also no conclusive evidence or only some indications for a reduction in hot flush frequency or severity (Nedrow et al., 2006; Lethaby et al., 2007; Jacobs et al., 2009; Bolanos et al., 2010; Eden, 2012; Lethaby et al., 2013), varying effects on spine bone mineral density and no effects on femoral neck, hip total and trochanter bone mineral density (Taku et al., 2010), and no protection against bone fracture (Kreijkamp‐Kaspers et al., 2004; Tempfer et al., 2007). The European Food Safety Authority (EFSA) eval‎uated the health claims related to the reduction of vasomotor symptoms and the maintenance of bone mineral density by soy isoflavones during menopause (EFSA NDA Panel, 2012). It was concluded that the available evidence was not sufficient to establish a relationship between the maintenance of bone mineral density and the consumption of soy isoflavones. Also, a relationship between the reduction of vasomotor symptoms associated with menopause and the consumption of soy isoflavones could not be established. EFSA eval‎uated 14 long‐term (>12 months) intervention studies on the effects of soy isoflavones on bone mineral density in post‐menopausal women. Of these studies, only two, reported an effect of soy isoflavones on bone mineral density and on markers of bone formation or resorption at doses of 54 mg per day (Morabito et al., 2002; Marini et al., 2007). The remaining 12 studies, testing doses of isoflavones up to 200 mg per day, showed no effects of soy isoflavones on bone mineral density or markers of bone formation or resorption [(EFSA NDA Panel, 2012) and references therein], although EFSA indicated that for some studies this negative result may have been due to the limited number of subjects included, resulting in an underpowered study.

EFSA also eval‎uated five human intervention studies in which soy isoflavones were administered for 6–9 months, and effects on bone mineral density were measured in peri‐/post‐menopausal women. One of these intervention studies revealed a beneficial dose–response effect on bone mineral density at the lumbar spine and femoral neck. Two of the studies reported a beneficial effect of soy isoflavones on bone mineral density at the lumbar spine, and two studies showed no effect of soy isoflavones on bone mineral density. EFSA concluded that ‘these studies provide some evidence for an effect of soy isoflavones on the attenuation of bone mineral density loss at the lumbar spine in post‐menopausal women when consumed for 6‐9 months’. Given the effects reported on parameters for bone formation and bone resorption, EFSA also concluded that these effects were possibly mediated by a decrease in bone resorption. However, taking all the evidence together, EFSA considered ‘the evidence insufficient to establish a cause and effect relationship between the consumption of soy isoflavones and maintenance of bone mineral density in post‐menopausal women’.

A later study reported by Greendale et al. (Greendale et al., 2015) investigated cross‐sectional and longitudinal relations between dietary intake of isoflavones and bone mineral density at the lumbar spine and femoral neck in Black, White, Chinese and Japanese women during the menopausal transition. In Japanese women, higher isoflavone intake appeared to be associated not only with higher peak femoral neck bone mineral density but also with greater rates of lumbar spine and femoral neck bone mineral density loss during the menopausal transition. Results for the other racial/ethnic groups did not support a relationship between dietary intake of isoflavones and either peak bone mineral density, or bone mineral density loss during the menopausal transition.

Altogether, it seems that the evidence for a beneficial effect of isoflavones and other phytoestrogens on bone mineral density in post‐ and peri‐menopausal women is limited and not convincing, and that they may even cause adverse effects, as indicated by the study of Greendale et al. (2015).

Effects of phytoestrogens on cardiovascular disease

In particular, the increase in cardiovascular risk and cardiovascular mortality upon sudden loss of ovarian function has provided a basis for the proposed role of oestrogens and phytoestrogens in the reduction in cardiovascular disease (Colditz et al., 1987; Parker et al., 2009). Reduced oestrogen levels during menopause may influence the development of obesity, fat distribution, the lipid profile in plasma, and rheological properties of plasma and platelet function (Gorodeski, 1994). These observations suggest that oestrogen deficiency may promote cardiovascular disease in women and trigger the idea that phytoestrogens may reduce the risk. The hypothesis is also supported by the low rates of cardiovascular diseases in Asian populations where the diet is particularly rich in soy, followed by the loss of this protection among the groups that have moved to Western societies (Nagata, 2000; Zhang et al., 2003). A meta‐analysis reported by Tokede et al. (2015) concluded that isoflavone supplementation had no effect on serum lipid profiles.

Oestrogens have been shown to influence atherosclerosis and the related clinical events in a differential way (Rossouw et al., 2007; Cano et al., 2010). They may act not only as protectors against atherosclerosis but also as potential disruptors of established atherosclerotic plaques, the latter being important hallmarks in the pathogenesis of the arterial forms of cardiovascular disease. The concept that phytoestrogens may act in a similar way comes from the observation that in Asian populations with high levels of their consumption, the preval‎ence of cardiovascular disease is lower than in populations in Western countries (Gonzalez Canete and Duran Aguero, 2014).

Cano et al. (2010) and also Gonzalez Canete and Duran Aguero (2014) reviewed the main evidence on the effects of isoflavones on the cardiovascular system at both the experimental and the clinical level. The review indicated that two clinical studies (van der Schouw et al., 2005; Kokubo et al., 2007) have examined the association of isoflavone intake with clinical cardiovascular events in a population without cardiovascular disease at baseline. One study concluded that high isoflavone intake was associated with reduced risk of cerebral and myocardial infarctions in Japanese women, with the risk reduction being especially pronounced in postmenopausal women (Kokubo et al., 2007). The second study was performed in a Western population and investigated whether a low intake of phytoestrogens would be associated with increased risks of cardiovascular disease (van der Schouw et al., 2005). The study concluded that an intake of isoflavones or lignans was not associated with decreased cardiovascular disease risk. However, when stratifying for ever versus never smokers, the risk of cardiovascular disease appeared to decrease with increased intake of lignans for ever smokers. The authors concluded that their data do not support the presence of a protective effect on cardiovascular disease risk of higher habitual intake of phytoestrogens, although for smokers a small risk reduction with higher lignan intake could not be excluded. In clinical practice, none of the phytoestrogens investigated have been proven to protect against cardiovascular disease (Tempfer et al., 2007).

Altogether, it can be concluded that it is not really clear if the administration of phytoestrogens in the early postmenopausal period may be protective for cardiovascular disease. For phytoestrogens, the current evidence appears poor compared to that available for oestrogens, and it is possible that the potential effect of oestrogens on the risk for stroke is not reproduced by isoflavones (Cano et al., 2010).

Effects of phytoestrogens on obesity, metabolic syndrome and type 2 diabetes

Dietary phytoestrogens have also been suggested to play a beneficial role in obesity, metabolic syndrome and type 2 diabetes (Bhathena and Velasquez, 2002; Cederroth and Nef, 2009; Crespillo et al., 2011; Jungbauer and Medjakovic, 2014; Struja et al., 2014). The meta‐analysis by Fang et al. (2016) reported an improvement in glucose metabolism and a significant reduction in insulin levels and insulin resistance in menopausal women, by especially genistein. Also, the meta‐analysis reported by Zhang et al. (2013) concluded that soy isoflavone supplementation could improve glucose metabolism and insulin control in non‐Asian postmenopausal women. Nutritional intervention studies in both animals and humans suggested that an intake of soy protein with isoflavones and flaxseed results in improved glucose control and insulin resistance (Bhathena and Velasquez, 2002; Cederroth and Nef, 2009; Jungbauer and Medjakovic, 2014). It is important to note that at present, it often remains unclear whether the beneficial effects are really due to the phytoestrogens or to some other dietary component in the soy protein and flax seed diet. The activation of PPAR‐mediated effects already mentioned above may provide a possible mode of action underlying these effects. However, as already concluded by Bhathena and Velasquez (2002), further investigations are needed to eval‎uate the long‐term effects of phytoestrogens on obesity, metabolic syndrome and type 2 diabetes.

Effects of phytoestrogens on breast cancer

The use of soy‐based preparations has been proposed for the prevention and treatment of certain types of cancer, such as for the prevention and treatment of breast cancer in women and prostate cancer in men (Eisenbrand et al., 2007). In contrast, clinical studies have reported data that suggest that isoflavones may via their oestrogenic and proliferative effects possibly raise breast cancer incidence in sensitive individuals (Petrakis et al., 1996; Hargreaves et al., 1999).

Meta‐analyses of epidemiological studies conducted in women consuming high‐soy diets concluded that there is a significant trend of decreased risk for breast cancer upon increasing intake of soy food (Trock et al., 2006; Wu et al., 2008; Dong and Qin, 2011; Chen et al., 2014). High lignan exposure has also been associated with a reduced breast cancer risk in postmenopausal women (Velentzis et al., 2009; Buck et al., 2010). Fritz et al. (2013) reported a systematic review and meta‐analysis on the potential effects of soy, red clover and isoflavone intake on breast cancer incidence and recurrence. The analysis included 40 randomized controlled trials, 11 uncontrolled trials and 80 observational studies. The authors concluded that soy consumption may be associated with reduced risk of breast cancer incidence, recurrence and mortality. Soy intake consistent with a traditional Japanese diet (2–3 servings a day containing 25–50 mg isoflavones) may also be protective against breast cancer and recurrence. Nevertheless, the authors also indicate that better evidence confirm‎ing the safety of isoflavones would be required before the use of high doses (≥100 mg) of isoflavones can be recommended for breast cancer patients. In addition, a nested case–control study and meta‐analysis of epidemiological studies revealed an inverse correlation between genistein intake and breast cancer (Taylor et al., 2009). It is important to note that this protective effect may originate from soy intake early in life (Warri et al., 2008; Hilakivi‐Clarke et al., 2010). Also of interest is the possible involvement of equol, a metabolite of daidzein produced by the human intestinal microflora, which may have similar beneficial effects on the incidence of breast cancer (Ingram et al., 1997; Goodman et al., 2009), although other studies have reported no or even adverse effects of equol (Magee, 2011). Given that only a limited percentage (30–40%) of the population has the ability to convert daidzein to equol, and taking into account that in vitro studies suggest equol to be more biologically active than its parent compound daidzein (Magee, 2011), it can be suggested that inter‐individual variation in response to daidzein may in part be related to variability in gut microflora composition resulting in inter‐individual differences in conversion of daidzein to equol. This existence of equol producers and non‐producers could provide an alternative explanation for interindividual differences in the response to phytoestrogens, since phytoestrogen metabolite formation by the gut microbiota can vary significantly between individuals with metabolites sometimes being more active than the parent phytoestrogen.

Also, the lignans enterodiol and enterolactone have been suggested to exert protective effects on breast cancer, possibly not only by oestrogen receptor‐dependent but also oestrogen receptor‐independent mechanisms (Mueller et al., 2004; Adlercreutz, 2007; Penttinen et al., 2007; Mense et al., 2008; Saarinen et al., 2010; Buck et al., 2011). There are also significant inter‐individual differences for enterodiol and enterolactone production due to different compositions of the gut microflora, which can cause a variation in the response of individuals to lignan precursors (Yoder et al., 2015). While coumestans are reported to be potent phytoestrogens in vitro, their effect on breast cancer is not known (Scarlata and Miksicek, 1995; Kuiper et al., 1998).

Recently, EFSA published a risk assessment for peri‐ and post‐menopausal women consuming food supplements containing isolated isoflavones (EFSA ANS Panel, 2015). EFSA eval‎uated especially the possible association between the isoflavone intake from food supplements and harmful effects observed in peri‐ and post‐menopausal women for the mammary gland, uterus and thyroid (EFSA ANS Panel, 2015). For the eval‎uation, EFSA selected 43 human studies and 62 animal studies. Among these studies were four epidemiological studies investigating breast cancer incidence (Rebbeck et al., 2007; Obi et al., 2009; Brasky et al., 2010; Boucher et al., 2013), eight interventional controlled studies, measuring mammographic density (Morabito et al., 2002; Atkinson et al., 2004; Marini et al., 2008; Powles et al., 2008; Verheus et al., 2008; Maskarinec et al., 2009; Colacurci et al., 2013; Delmanto et al., 2013), and two interventional controlled studies, investigating histopathological changes (Cheng et al., 2007; Khan et al., 2012). These studies did not reveal an association between isoflavone exposure and adverse effects in the mammary gland (EFSA ANS Panel, 2015). Of the 11 animal studies that investigated histopathological changes in the mammary gland upon treatment with isoflavones and the 10 studies in ovariectomized animals that investigated breast cell proliferation, the majority did not reveal an effect (EFSA ANS Panel, 2015). Only in two of the studies in ovariectomized rats, a stimulating effect on the mammary gland was observed after 90 days of dosing with genistein at 5.4 and 54 (Rimoldi et al., 2007) and 221 mg.kg bwt−1.day−1 (Wuttke et al., 2006). EFSA concluded that these findings were ‘consistent with the results from the US National Toxicology Program study conducted in non‐ovariectomized animals administered genistein at doses ranging 0.3–44 mg.kg bwt−1.day−1 (NTP, 2008), in which there was some evidence of carcinogenic activity of genistein in female rats based on an increased incidence of mammary gland adenoma or adenocarcinoma’. EFSA also indicated that the human data from observational studies did not point at an increased risk of breast cancer in menopausal women but specifically also noted that this conclusion cannot be extended to the risk of oestrogenic isoflavones‐based food supplements for postmenopausal women who have a diagnosis or history of oestrogen‐dependent cancer. Also, other endpoints considered did not reveal any effect except for some non‐malignant histopathological changes in mammary tissue after 60 months supplementation at 150 mg·day−1 of soy isoflavones which is high compared with the current estimated daily intakes.

Thus, concerns still exist that the oestrogenic activity of phytoestrogens may present a risk to patients with oestrogen‐sensitive breast cancer and to women that are at a high risk of developing breast tumours (Messina, 2008; Hilakivi‐Clarke et al., 2010), and it remains to be stablished whether exposure to isoflavones reduces or increases breast cancer risks.

Effects of phytoestrogens on other forms of cancer including prostate cancer, bowel cancer, uterine cancer and other cancers

Epidemiological studies and a nested case–control study carried out in Japan reported that isoflavone intake might be associated with a decreased risk of lung cancer (Shimazu et al., 2011). This observation also follows from a meta‐analysis indicating that the consumption of soy food is associated with lower lung cancer risk (Yang et al., 2011). Another nested case–control study performed with the Korean Multicenter cancer cohort revealed that high serum concentrations of isoflavones were associated with a decreased risk for gastric cancer (Ko et al., 2010). Furthermore, several studies report a negative correlation between prostate cancer incidence and a phytoestrogen rich diet containing lignans and/or isoflavones (Severson et al., 1989; Adlercreutz, 1995; Kurahashi et al., 2007), and a meta‐analysis revealed that the consumption of soy foods or genistein and daidzein is associated with a reduction in prostate cancer risk in men (Hwang et al., 2009; Yan and Spitznagel, 2009; He et al., 2015). Another meta‐analysis reported by Van Die et al. (2014) concluded that there is a potential role for soy and soy isoflavones in reducing risks for prostate cancer, but that a clear understanding could not be derived from the data because of limitations in sample size and study duration in the individual trials. Also equol, the gut microbiome metabolite of the soy isoflavone daidzein was suggested to have beneficial effects on the incidence of prostate cancer (Akaza et al., 2004; Ozasa et al., 2004). Epidemiological studies suggest that high dietary intake of phytoestrogens in pre‐ and post‐menopausal women is correlated with reduced thyroid cancer risk (Horn‐Ross et al., 2002; Haselkorn et al., 2003). For oestrogens in general, increased exposure has been linked to an increased risk of developing uterus cancer in women (Persson, 2000), and of prostate and testicular cancer in men (Bonkhoff et al., 1999; Maffini et al., 2006). Women who consume a diet rich in isoflavones or soy may have a lower risk of endometrial and ovarian cancer (Eden, 2012; Qu et al., 2014; Zhang et al., 2015).

The risk assessment for peri‐ and post‐menopausal women taking isoflavone‐containing food supplements performed by EFSA (EFSA ANS Panel, 2015) also eval‎uated the possible association between the intake of isoflavones from food supplements and harmful effects on the uterus. EFSA reported that there was no study on the association between isoflavone intake and risk of uterine cancer in the target population. As surrogate markers, data on endometrial thickness reported in 25 interventional controlled studies and on histopathology of the endometrium presented in nine interventional controlled studies were eval‎uated (EFSA ANS Panel, 2015). No significant adverse effects were observed in any of the human intervention studies, at dose levels up to 150 mg isoflavone·day−1 for 2.5 years. Thirteen studies in animals investigated cell proliferation in the uterus, and 22 animal studies studied uterus histopathological changes. No adverse effects were seen in any of the studies. EFSA concluded that the human and animal studies support that in post‐menopausal women adverse effects on the uterus were not noted for soy isoflavones, but that in the absence of data on the effect on uterine cancer, it was not possible to draw conclusions on effects of isoflavones on the uterus in peri‐menopausal women (Horn‐Ross et al., 2002; Haselkorn et al., 2003).

Effects of phytoestrogens on the thyroid and thyroid function

The soy isoflavones daidzein and genistein are reported to inhibit thyroid peroxidase (TPO) in vitro (EC number 1.11.1.8), an enzyme involved in the synthesis of T3 and T4 (Divi et al., 1997). Also in rats in vivo, daidzein and genistein inhibit TPO activity; however, no other adverse effects on thyroid functions could be observed (Chang and Doerge, 2000; Doerge and Sheehan, 2002). In addition, oestrogens are implied to have indirect effects on thyroid function, which has led to the concern that phytoestrogens may adversely affect thyroid function. However, human studies on the effect of soy isoflavones on thyroid function reviewed by EFSA (EFSA ANS Panel, 2015) are not conclusive. Some studies suggest that risk factors, such as iodine deficiency and subclinical hypothyroidism, might increase susceptibility of individuals to potential adverse effects of soy isoflavones on thyroid function (Doerge and Sheehan, 2002; Sathyapalan et al., 2011).

Effects of phytoestrogens on brain function

Most studies on the effect of phytoestrogens on neurological endpoints are conducted with soy isoflavones, while few studies also addressed the effects of dietary lignans. The rationale behind such studies is that oestrogens play an important role in brain health. The brain controls oestrogen release through the hypothalamus–pituitary–gonadal axis and also responds to oestrogens. In addition, oestradiol plays a key role in the neurobiology of ageing, because endocrine and neural senescence overlap in time and are mechanistically intertwined in complex feedback loops (Morrison et al., 2006). For oestrogen therapy, there are conflicting results on whether protective or detrimental effects on brain health are exerted. The reasons for the different observations appear to lie in the time at which oestrogen therapy is initiated, the neurological status of the brain at the time of oestrogen therapy initiation and the type of therapy used (Brinton, 2004). Interestingly, the loss of especially ERα seems to be associated with reduced neuroprotection by E2, and there appears to be a beneficial role for ERα in the aging brain (Schreihofer and Ma, 2013). A literature review on the neuroprotective effects of phytoestrogens found in soy reports that, while it has been demonstrated in animal research and cell culture studies that phytoestrogens from soy can exert neuroprotective effects, clinical trials and observational studies in humans have produced inconclusive findings (Soni et al., 2014). In this review, seven observational studies were reviewed; of which, three found positive effects of isoflavones on cognition (Hogervorst et al., 2008; Hogervorst et al., 2011; Greendale et al., 2012). Out of the 12 randomized control trials reviewed, six reported beneficial effects of isoflavone treatment on cognitive function (File et al., 2001; Duffy et al., 2003; Kritz‐Silverstein et al., 2003; Casini et al., 2006; Gleason et al., 2009; Thorp et al., 2009). Despite positive findings of studies investigating phytoestrogens and cognition, approximately half of the reviewed studies demonstrate negative or null effects (Soni et al., 2014). Just like for oestrogen therapy, also for phytoestrogens, there are many factors that have an effect on the outcomes, like age, gender, ethnicity, and menopausal status, as well as duration of consumption, and the cognitive test used. One important characteristic of the study population is the metabolic capacity to produce equol, which differs between Asian and non‐Asian study populations, and generally declines with age (Soni et al., 2014).

Consumption of soy or soy isoflavones has been shown to affect various endpoints related to neuronal health in rats (Zeng et al., 2004; Azcoitia et al., 2006; Huang and Zhang, 2010; Neese et al., 2010; Pan et al., 2010; Bagheri et al., 2012), and in mice (Zhao and Brinton, 2009; Bansal and Parle, 2010; Zhao et al., 2011; Yao et al., 2013), while consumption of large doses are also reported to have negative effects on the brain of rats (Choi and Lee, 2004). It is of interest to note that the protective effects of genistein on the cerebral cortex of ageing rats were suggested to have a different mode of action than that of oestradiol (Moran et al., 2013).

Different lignans have shown positive effects on cognitive performance and markers of Alzheimer's disease in mice (Um et al., 2009; Giridharan et al., 2011; Hu et al., 2012; Jeong et al., 2013; Li et al., 2014; Mao et al., 2015). In observational studies in humans, higher dietary intake of lignans is associated with better cognitive function (Franco et al., 2005; Kreijkamp‐Kaspers et al., 2007; Greendale et al., 2012; Nooyens et al., 2015), while coumestrol ingestion was unrelated to cognitive performance (Greendale et al., 2012).

Altogether, the data presented on possible beneficial effects of phytoestrogens on neurological health are inconclusive and seem to be affected by various factors. Furthermore, it is not clear, whether the observed beneficial effects are due to an oestrogen‐like mode of action, or whether other mechanisms underlie these effects.

Discussion

Many health effects including both benefits and risks have been related to exposure to phytoestrogens. Reported benefits include a lowered risk of menopausal symptoms, cardiovascular disease, breast cancer, other forms of cancer including prostate cancer, bowel cancer, uterine cancer and other cancers, and brain function disorders. On the other hand, phytoestrogens are also considered endocrine disruptors, indicating that they have the potential to cause adverse health effects such as infertility and increased risks of cancer in oestrogen‐sensitive organs. These adverse effects have been mainly suggested based on data from in vitro, animal or epidemiological studies. Clinical studies often report the absence of adverse effects. Tempfer et al. (2009) reported a meta‐analysis on possible side effects of phytoestrogens. Based on 174 randomized controlled trials, it was concluded that phytoestrogen supplements have a safe side effect profile with moderately elevated rates of gastrointestinal side effects. It is important to note, however, that these studies were generally not designed to study the safety of the phytoestrogens.

Consequently, the question of whether phytoestrogens are beneficial or harmful to human health remains of importance. The present overview reveals that the answer is rather complex and may depend on age, health status, and even the presence or absence of specific gut microflora in the population of concern. To further illustrate this complexity, Figure 5 presents a cartoon summarizing the possible health effects of phytoestrogens and the potential underlying modes of action as presented in the present paper.

Figure 5.

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Schematic presentation summarizing the possible health effects of phytoestrogens and the potential underlying modes of action as presented in the present paper.

Given the rapid increase in global consumption of phytoestrogens and the fact that phytoestrogens are present in a wide range of dietary food supplements and widely marketed as a natural alternative to oestrogen replacement therapy, further insight into the risks and benefits of these phytoestrogens seems essential. Additional issues to be taken into account in the near future include (i) effects on children since phytoestrogens may be present in for example soy based infant foods; (ii) the role of the gut microbiota in phytoestrogen metabolism and differences in this microbial metabolism and the consequences for the health effects; (iii) the role of possible other modes of action than the oestrogenic activity in the health effects of phytoestrogens; (iv) the physiological levels of the phytoestrogens and their metabolites and how these relate to concentrations required in in vitro cellular models to actually induce the different effects; (v) the role of polymorphisms in the differential biological effects of phytoestrogens and the possible contribution of ‐omics technologies to elucidate these effects; and (vi) the fact that most phytoestrogens are weak oestrogens with anti‐oestrogenic effects when they compete with endogenous oestrogens for binding to the ERs, but pro‐oestrogenic effects in the absence of endogenous oestrogens and uncertain effects in the presence of low concentrations of endogenous oestrogens as occurs in the menopause.

The current review presents an overview of the potential health benefits of dietary phytoestrogens. It is of interest to put the observations within the guidance developed by EFSA for performing risk–benefit assessments of food. Given that in Europe food supplements are considered food this seems appropriate. EFSA recommended a stepwise approach for the risk–benefit assessment including first an assessment of whether the health risks clearly outweigh the health benefits or vice versa. The literature overview presented in this paper illustrates that at the current state‐of‐the‐art the beneficial health effects are not so obvious that they clearly outweigh the possible health risks. This implies that a further refinement of the assessment would be required, aiming at providing semi‐quantitative or quantitative estimates of risks and benefits at relevant exposures by using common metrics, and a comparison of risks and benefits using a composite metric such as disability‐adjusted life years or quality‐adjusted life years to express the outcome of the risk–benefit assessment as a single net health impact value. The currently available data set is not sufficient to support such a refined (semi) quantitative analysis. Taking all together, it can be concluded that several potential health benefits of phytoestrogens have been reported but that, given the data on potential adverse health effects, the current evidence on these beneficial health effects is not so obvious that they clearly outweigh the possible health risks. This implies that a definite conclusion on possible beneficial health effects of phytoestrogens cannot be made.

Author contributions

All authors contributed equally to writing the review.

Conflict of interest

The authors declare no conflicts of interest.

Supporting information

Table S1 binding affinity of E2 and phytoestrogens to ERα and ERβ (expressed as IC50 values from competitive binding assays).

Table S2 ERα‐ and ERβ‐ mediated gene expression‎ induced by E2 and phytoestrogens (expressed as EC50 values from reporter gene assays).

Supporting info item

Click here for additional data file. (81.2KB, pdf)

Rietjens, I. M. C. M. , Louisse, J. , and Beekmann, K. (2017) The potential health effects of dietary phytoestrogens. British Journal of Pharmacology, 174: 1263–1280. doi: 10.1111/bph.13622.

References