Journal of Chromatography B (v.777, #1-2)
Review of the methods used in the determination of phytoestrogens by Chao-Cheng Wang; Jeevan K Prasain; Stephen Barnes (3-28).
Interest in analytical methods for plant estrogens (phytoestrogens) has risen sharply in the past 10 years. In this review, we examine the existing analytical methods based on separations by gas–liquid chromatography, high-performance liquid chromatography and capillary electrophoresis in addition to methods of detection by ultraviolet absorption, fluorescence, electrochemical oxidation/reduction and mass spectrometry. These methods are compared with other methods of phytoestrogen analysis utilizing immunoassay approaches. The advantages and disadvantages of each of these methods are highlighted and potential areas for further development identified.
Enterolignans by B Raffaelli; A Hoikkala; E Leppälä; K Wähälä (29-43).
A review with 114 references about mammalian lignans (enterolignans). Several aspects have been reviewed: the precursors of mammalian lignans and their biosynthesis, biological activities and health effects, metabolism (in vivo and in vitro) in human and animals, some synthetic strategies to obtain enterolignan skeleton types, including the synthesis of haptens and deuterated lignans, and finally an overview of the analytical methods to detect and quantify lignans in biological matrices and foods.
Liquid chromatographic–photodiode array mass spectrometric analysis of dietary phytoestrogens from human urine and blood by Adrian A Franke; Laurie J Custer; Lynne R Wilkens; Loı̈c Le Marchand; Abraham M.Y Nomura; Marc T Goodman; Laurence N Kolonel (45-59).
Dietary phytoestrogens have been implicated in the prevention of chronic diseases. However, it is uncertain whether the phytoestrogens or the foods associated with phytoestrogens account for the observed effects. We report here a new liquid chromatography photodiode array mass spectrometry (LC–PDA-MS) assay for the determination of nanomolar amounts of the most prominent dietary phytoestrogens (genistein, dihydrogenistein, daidzein, dihydrodaidzein, glycitein, O-desmethylangolensin, hesperetin, naringenin, quercetin, enterodiol, enterolactone) in human plasma or serum and urine. This assay was found to be suitable for the assessment of quercetin exposure in an onion intervention study by measuring urinary quercetin levels. Other successful applications of this assay in clinical and epidemiologic studies validated the developed method and confirmed previous results on the negative association between urinary isoflavone excretion and breast cancer risk.
Determination of matairesinol in flax seed by HPLC with coulometric electrode array detection by Tanja Kraushofer; Gerhard Sontag (61-66).
A HPLC method coupled with coulometric electrode array detection for the determination of matairesinol in flax seed is described. The defatted sample was spiked with bisphenol A (internal standard), refluxed for 75 min in a mixture of ethanol–bidistilled water–12 M hydrochloric acid (2:2:1, v/v/v) to extract matairesinol conjugates and to hydrolyze them simultaneously. The extract was diluted with mobile phase [250 ml acetonitrile–750 ml buffer (730 ml bidistilled water, 20 ml glacial acetic acid adjusted to pH 3 with 5 M sodium hydroxide)] and injected into the HPLC system. Matairesinol was separated from other compounds on a reversed-phase column (Lichrospher 60 RP-Select B, 250×4 mm, 5 μm) and detected in a coulometric electrode array detector using a flow-rate of 0.8 ml/min. The potentials of the eight electrodes were set on +150, +200, +250, +300, +350, +400, +550 and +600 mV against modified palladium electrodes. The content of matairesinol determined in seven samples varies between 7 and 28.5 μg/g. The limit of quantitation is 5 μg/g.
Concept of sequential analysis of free and conjugated phytosterols in different plant matrices by Patrick Breinhölder; Livia Mosca; Wolfgang Lindner (67-82).
A unique concept and method for the determination of the total plant sterol content as sum of free sterols (FS), steryl esters (SE), steryl glycosides (SG) and acylated steryl glycosides (ASG) in different plant materials (pumpkin seeds, lecithins) and phytopharmaceuticals derived thereof, was developed. For this purpose, a multidimensional sample clean-up protocol based on efficient solid-phase extraction materials was elaborated and the SG were isolated employing a novel phenyl boronic acid modified silica gel material. Along this line also a set of steryl glucosides was synthesised and employed as internal standard and for calibration in the course of quantitative analysis. Final quantification of SG was carried out with reversed-phase HPLC in combination with evaporative light scattering detection (ELSD); the ASG were determined after conversion to SG by mild alkaline hydrolysis. In order to determine the total plant sterol profile the sum of FS and SE was additionally analysed from the unsaponifiable lipid fraction by GC–FID. The yields obtained from recovery tests for the determination of SG using soya lecithin as matrix to which 2, 20 and 40 mg/g of cholesterol-β-d-glucoside was added were 99.10, 98.07 and 90.00%, and the RSDs were 4.11, 2.62 and 4.50%, respectively. Application related to the qualitative and quantitative analysis of total phytosterol profiles in different plant matrices and extracts demonstrate the validity of the method.
Keywords: Phytosterols; Phytosteryl glycosides;
Determination of thermo-oxidation products of plant sterols by Anna-Maija Lampi; Laura Juntunen; Jari Toivo; Vieno Piironen (83-92).
Plant sterols are subjected to oxidation when exposed to air and, especially, when heated at high temperatures. We developed a method to study thermo-oxidation of plant sterols. The method consisted of cold saponification, purification of oxides by solid-phase extraction and gas chromatography analysis. To compensate for losses during the procedure, an internal standard was added before saponification. The method showed good recovery of added cholesterol oxides, separation of plant sterol oxides and reproducibility in detecting thermo-oxidation products of stigmasterol and rapeseed oil. Based on this study, the major products are 7-hydroxy, 5,6-epoxy and 7-keto compounds and oxides are formed faster in bulk stigmasterol than in rapeseed oil.
Identification and quantification of polyphenol phytoestrogens in foods and human biological fluids by A.P Wilkinson; K Wähälä; G Williamson (93-109).
We review the methods used to measure phytoestrogens (genistein, daidzein, lignans and their derivatives) in foods and biological fluids, and discuss advantages and disadvantages of each. The range of detection limits reported varies widely between individual laboratories, but generally the best reported sensitivity is as follows: immunoassay>HPLC–mass spectrometry=HPLC–multichannel electrochemical detection (coularray)>GC–single ion monitoring-mass spectrometry>HPLC–UV diode array>HPLC–single channel electrochemical detection. The best sensitivity reported so far is 0.002 pmol per assay for daidzein by radioimmunoassay. HPLC with UV diode array detection is the most commonly employed, but is the least sensitive and specific. GC and HPLC coupled with mass spectrometry or electrochemical detection are the most accurate and reproducible methods for a wide variety of analytes. Generally most methods, with the exception of immunoassay, have not been correlated with other methods. Recoveries from extraction methods, limits of detection, nature of compounds analysed and the internal standards used are summarised for more than 90 reports in the literature. From this data, it is clear that an inter-laboratory validation and correlation between a wide range of methods for phytoestrogen analysis is required. One underdeveloped area that requires particular attention is the analysis of plant lignans.
Keywords: Polyphenol phytoestrogens;
Deuterated phytoestrogen flavonoids and isoflavonoids for quantitation by K. Wähälä; S. Rasku; K. Parikka (111-122).
Isotopically and isomerically pure polydeuterated flavonoids and isoflavonoids have been prepared for quantitation of these compounds in biological matrices. Various deutero-labeling techniques are presented and methods for establishing the isotopical and isomerical purity of deuterated products are discussed.
Keywords: Phytoestrogens; Flavonoids; Isoflavonoids;
Quantification of isoflavones in red clover by high-performance liquid chromatography by Liselotte Krenn; Iris Unterrieder; Renate Ruprechter (123-128).
An RP–HPLC method for the determination of daidzein, genistein, formononetin and biochanin A in red clover (Trifolium pratense L.) was developed and validated. The compounds are quantified after hydrolytic extraction using an internal standard. On a base-deactivated C18 column good separation of the analytes, also from accompanying substances, and excellent peak shape are achieved by gradient elution with aqueous sulfuric acid and acetonitrile. The method was applied to the analysis of different red clover cultivars.
Solvent extraction selection in the determination of isoflavones in soy foods by Patricia A Murphy; Kobita Barua; Catherine C Hauck (129-138).
Acetonitrile is superior to acetone, ethanol and methanol in extracting the 12 phytoestrogenic soy isoflavone forms found in foods. At 53% organic solvent in water, raw soy flour, tofu, tempeh, textured vegetable protein and soy germ were evaluated for isoflavone extraction efficiency. The efficiency of acetonitrile extraction was demonstrated in mass balance evaluations of toasting of soy flour and soymilk heating.
High-throughput quantification of soy isoflavones in human and rodent blood using liquid chromatography with electrospray mass spectrometry and tandem mass spectrometry detection by Nathan C Twaddle; Mona I Churchwell; Daniel R Doerge (139-145).
Soy-containing foods and dietary supplements are widely consumed for putative health benefits (e.g., cancer chemoprevention, beneficial effects on serum lipids associated with cardiovascular health, reduction of osteoporosis, relief of menopausal symptoms). However, studies of soy isoflavones in experimental animals suggest possible adverse effects as well (e.g., enhancement of reproductive organ cancer, modulation of endocrine function, anti-thyroid effects). This paper describes the development and validation of a sensitive high throughput method for quantifying isoflavones in blood from experimental animal and human studies. Serum samples containing genistein, daidzein, and equol were processed using reverse phase solid-phase extraction in the 96-well format for subsequent LC–ES/MS/MS or LC–ES/MS analysis using isotope dilution in conjunction with labeled internal standards. The method was validated by repetitive analysis of spiked blank serum and the intra-day and inter-day accuracy (88–99%) and precision (relative standard deviations from 3 to 13%) of measurement determined. The lower limit of quantification for all isoflavones was approximately 0.005 μM using MS/MS detection, and 0.03 μM using MS for genistein and daidzein. The degree of method performance, with respect to throughput, sensitivity and selectivity, makes this approach practical for analysis of large sample sets generated from mechanistic animal studies and human clinical trials of soy isoflavones.
Simultaneous determination of hypericin and hyperforin in human plasma and serum using liquid–liquid extraction, high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry by R Pirker; C.W Huck; G.K Bonn (147-153).
A method for the simultaneous extraction of hypericin and hyperforin from a St. John’s Wort extract, which is used in case of moderate depressions and skin injuries, from human plasma and serum by liquid–liquid extraction (LLE) with n-hexane–ethylacetate (70:30, w/w) was developed. A reversed-phase high-performance liquid chromatographic (RP-HPLC) method with UV, fluorescence (FLD) and mass spectrometric (MS) detection using electrospray ionization (ESI) was used to identify and quantify hypericin and hyperforin in the extracts from blood samples. Linearity was obtained in the ranges 8.4–28.7 ng/ml (hypericin) and 21.6–242.6 ng/ml (hyperforin). Recoveries were between 32.2 and 35.6% for hypericin and 100.1 and 89.9% for hyperforin. Intra-day accuracy and precision for this method ranged between 3.2 and 4.3% and 2.6 and 2.8%, respectively. After validation of the LLE, the method was tested on real plasma samples which were obtained by ingestion of St. John’s Wort extract capsules. Blood samples were taken 2, 4, and 6 h after ingestion. Finally, this method proved to be highly suitable for clinical and pharmacologically relevant studies.
Keywords: Hypericin; Hyperforin;
Overview of in vitro tools to assess the estrogenic and antiestrogenic activity of phytoestrogens by Stefan O Mueller (155-165).
There is an intense discussion in the scientific and even more so in the public community as well as regulatory agencies about the potential benefits or detrimental effects of plant-derived compounds that may affect the endocrine system, especially estrogen signaling pathways. These so-called phytoestrogens are found in the normal western diet and predominantly in an eastern or soy-based diet and the potency of the isolated compounds to interact with the known receptors for estrogen varies tremendously. The estrogen receptors, ERα and ERβ, mediate the effects of endogenous estrogens, i.e. regulation of reproductive function, tissue development, cell proliferation and differentiation. In this review, in vitro test systems available to date for the screening of estrogenic and antiestrogenic activity including mechanism-based assays are described. The potency of phytoestrogens determined using these in vitro assays are compared with the potency of endogenous estrogens and results obtained in vitro are compared with effects in vivo. Finally, the impact of in vitro assays to determine estrogenicity on human hazard assessment is discussed as well as other non ER-mediated mechanisms that may contribute to potential beneficial or adverse effects of phytoestrogens in man.
Keywords: Phytoestrogens, activity;
Yeast reporter system for rapid determination of estrogenic activity by Alois Jungbauer; Verena Beck (167-178).
An in vitro test system for the determination of estrogens, xeno- and phytoestrogens, based on the activation of human estrogen receptor-α, has been examined for ability in monitoring environmental estrogens. The system consists of an expression plasmid for the human estrogen receptor-α and a reporter plasmid containing the lacZ gene under the control of the vitellogenin hormone response element. These plasmids have been transformed into S. cerevisae. Cultivation of yeast in the presence of estrogenic substances leads to activation of the estrogen receptor and induces the expression of the reporter lacZ. β-Galactosidase activity of the translated gene lacZ is a measure of the estrogenic activity of a compound. First, the selectivity of the system was compared to data available in the literature. Then the sensitivity of the system was checked. The detection limit is 0.1 ng 17-β estradiol or an equivalent activity per liter, if a sample can be concentrated 1000-fold. The system has been further characterized by selected compounds with known and unknown estrogenic activity.
Keywords: Estrogen; Phytoestrogens; Xenoestrogens;
Assessing estrogenic activity of phytochemicals using transcriptional activation and immature mouse uterotrophic responses by Wendy N Jefferson; Elizabeth Padilla-Banks; George Clark; Retha R Newbold (179-189).
The estrogenic responses of several phytoestrogens including genistein, daidzein, coumestrol, α-zearalanol, zearalenone, naringenin, taxifolin and biochanin A were compared over a wide dose range using an in vitro assay that measures transcriptional activation of the estrogen receptor (ER) and an in vivo immature mouse uterotrophic assay consisting of measuring uterine wet weight increase plus sensitive morphological and biochemical endpoints in the uterus. The transcriptional activation assay showed activation of the ER by all compounds tested except taxifolin with varying magnitudes of response as compared to estradiol or diethylstilbestrol. Results from the uterotropic bioassay showed that genistein, coumestrol, zearalanol, and zearalenone caused an increase in uterine wet weight, while naringenin, taxifolin, daidzein and biochanin A failed to do so over the dose range tested. However, sensitive morphological and biochemical parameters such as uterine epithelial cell height increase, uterine gland number increase, and induction of the estrogen-responsive protein lactoferrin demonstrated that all compounds tested in this study gave some measure of estrogenicity although a wide range of estrogenic responses across compounds was shown. Use of multiple in vitro and in vivo estrogenic endpoints as described in this paper will be useful in developing estrogenic profiles for individual compounds and ultimately mixtures of compounds. Furthermore, having an estrogenic “fingerprint” for each phytochemical is an essential first step in determining potential adverse effects of exposure to phytoestrogens.
Keywords: Phytoestrogens; Diethylstilbestrol; Estrogen receptor; Lactoferrin;
In vivo test systems for the quantitative and qualitative analysis of the biological activity of phytoestrogens by P Diel; S Schmidt; G Vollmer (191-202).
Many compounds of plant origin with the ability to bind to the estrogen receptor have been identified in the last decades. One of the most extensively used in vivo assays to characterise the estrogenic potency of these phytoestrogens and mechanisms of their action is the rodent uterotrophic assay. Various protocols exist for this test system, using immature, hypophysectomized, or ovariectomized rats and mice and oral or subcutaneous administration of the test compound. However, just monitoring the ability of a compound to stimulate uterine growth is not sufficient to characterize its estrogenicity. Over the last decades, an increasing number of estrogen sensitive tissues has been identified. Moreover, a variety of different molecular mechanisms have been discovered for the action of estrogens, including non-genomic actions. Therefore, an in vivo test design for estrogenicity should include an analysis of several estrogen sensitive parameters in different estrogen sensitive tissues. To distinguish between agonistic and antagonistic properties of a substance, combinations of the test compound with estrogens and antiestrogens should be analyzed. A reasonable supplement to this enhanced uterotrophic assay are selected estrogen sensitive tumor models, which can be used to test for potential chemopreventive properties of phytoestrogens.
Bioavailability of isoflavones by Suzanne Hendrich (203-210).
Isoflavones are disease protective components of soybeans. Isoflavone metabolism and bioavailability are key to understanding their biological effects. Isoflavone glucuronides, dominant biotransformation products in humans that are more hydrophilic than isoflavone aglycones, activate human natural killer cells in vitro but are less toxic to NK cells than the parent aglycones. Gut microbial isoflavone metabolites have also been identified, but remain to be well characterized. Gut transit time (GTT) seems to be a significant determinant of isoflavone bioavailability because women with more rapid GTT (<40 h) experienced 2–3-fold greater absorption of isoflavones than did women with longer GTT (>65 h). Isoflavone metabolism varies a great deal among individuals, thus limiting the quantitative value of urine or plasma isoflavones as biomarkers of soy ingestion. Defining and lessening interindividual variation in isoflavone bioavailability, and characterizing health-related effects of key isoflavone metabolites are likely to be crucial to further understanding of the health benefits of isoflavones.
Oxidative metabolism and genotoxic potential of major isoflavone phytoestrogens by Sabine E Kulling; Leane Lehmann; Manfred Metzler (211-218).
The soy isoflavones daidzein, genistein and glycitein are extensively metabolized by rat liver microsomes to a variety of catechol metabolites. Hydroxylated metabolites of daidzein and genistein have also been demonstrated in incubations with human hepatic microsomes and in the urine of humans after ingestion of soy food. Although the microsomal metabolism of formononetin and biochanin A is dominated by demethylation to daidzein and genistein, respectively, catechols of the parent isoflavones and of the demethylation products are also formed. Thus, oxidative metabolism appears to be common among isoflavones and may have implications for their biological activities. As genistein but not daidzein exhibits clastogenic activity in cultured mammalian cells, the role of oxidative metabolism for the genotoxicity of isoflavones is of particular interest.
Keywords: Isoflavone phytoestrogens;
Flavonoids and steroid hormone-dependent cancers by Rachel S Rosenberg Zand; David J.A Jenkins; Eleftherios P Diamandis (219-232).
Steroid-hormone dependent cancers, including those of the breast, prostate and colon, are leading causes of morbidity and mortality in western countries. In rural Asian areas, these diseases are relatively uncommon. Dietary factors, including low consumption of fruit, vegetables and soy in the west have been shown in various epidemiologic studies as reasons for these differences. This review discusses flavonoids, one component of these plant foods that is being investigated for their role in chemoprevention. Epidemiological, in vitro, animal and human studies shall be explored to look at mechanisms involved, including steroid hormone activity, effects on cell growth, antioxidant activities, inhibition of chemical carcinogenesis and influences on modulators of cancer risk. Although the in vitro and animal models point to several pathways by which flavonoids may reduce incidence of these cancers, the clinical data are still relatively lacking. More research is needed to determine how best to use foods containing these compounds to reduce steroid hormone-dependent cancer risk.
Keywords: Flavonoids; Steroids;
Phytoestrogens as modulators of steroid action in target cells by C. Benassayag; M. Perrot-Applanat; F. Ferre (233-248).
Although numerous reports exist on the potential beneficial role of nutritional phytoestrogens in human health, their molecular mechanism in target cells is still not completely understood. Phytoestrogens promote estrogen and antiestrogen effects by interacting with numerous molecules, carrier proteins, enzymes and membrane and nuclear receptors, directly or indirectly involved in the transfer of estrogen signals. The hypothesis that the ERβ subtype plays a key role in antiproliferative effect of phytoestrogens, especially in breast cancer, is examined here.This review focus on the effects of phytoestrogens in developmental processes such as those linked to reproductive function, tumorigenesis and angiogenesis.
Keywords: Phytoestrogens; Steroids;
Estrogen receptor expression in the prostate of rats treated with dietary genistein by Abraham Dalu; Betty S Blaydes; Corey W Bryant; John R Latendresse; Constance C Weis; K Barry Delclos (249-260).
Steroid hormones and their receptors play critical roles in the growth, development, and maintenance of the male reproductive tract. Genistein, a naturally occurring isoflavonoid primarily found in soybeans, interacts with estrogen receptors α and β (ERα and β), with preferential affinity for ERβ. This is one mechanism whereby genistein may affect growth and development and potentially alter susceptibility to carcinogenesis. Previous studies have indicated effects of soy and/or genistein in the male rodent reproductive tract under certain exposure conditions. The current study was undertaken to determine if modulation of the expression of ERα and ERβ by dietary genistein may contribute to those effects. Rats in a two-generation study were fed 0, 5, 100, or 500 ppm genistein prior to mating and through pregnancy and lactation. At weaning, male pups were selected in each of the F1 and F2 generations and half of the pups continued on the same diet as their dams (G/G, continuous exposure) while their litter mates were placed on control chow (G/C, gestational and lactational exposure) until sacrifice on PND 140. Male reproductive organ weights, serum levels of testosterone and dihydrotestosterone (DHT), and ERα and ERβ protein levels in the ventral and dorsolateral prostate were the endpoints measured. Prostate sections were also evaluated microscopically. Statistically significant elevations in testosterone and DHT were observed in PND 140 animals from the F1 generation, but they were not accompanied by organ weight changes. Body weight in the continuously dosed 500 ppm F1 PND 140 animals was depressed relative to control, but organ weights in animals of either generation showed few treatment-related effects. While estrogen receptor levels were quite variable, levels of ERβ in the dorsolateral prostate were significantly depressed in all dose groups in the G/C exposure and the high dose group of the G/G exposure in F1 rats, but not in F2 rats. Given the growing body of knowledge on the significance of ERβ in the prostate, the evidence for apparent down regulation of this receptor by genistein may have implications for reproductive toxicity and carcinogenesis that warrant further investigation.
Isoflavonoids inhibit catabolism of vitamin D in prostate cancer cells by Hesso Farhan; Kristiina Wähälä; Herman Adlercreutz; Heide S Cross (261-268).
The high ingestion of soybean products in Asian countries has been suggested to be responsible for a reduced incidence of prostate cancer. The mechanism of action, however, is unknown. Our data demonstrate that genistein and some isoflavone metabolites reduce the activity of 25-D3-24-hydroxylase (CYP24) in the human prostate cancer-derived cell line DU-145. CYP24 is also responsible for degradation of the active vitamin D metabolite 1,25-dihydroxyvitamin D3 which is known to be antimitotic and prodifferentiating in prostate cancer cells. High levels of CYP24 frequently found in prostate cancer cells may thus degrade the active metabolite. This could be prevented by ingestion of genistein-containing food such as soybeans.
Keywords: Isoflavonoids; Vitamin D;
Inactivation of thyroid peroxidase by soy isoflavones, in vitro and in vivo by Daniel R Doerge; Hebron C Chang (269-279).
Soy-containing foods and dietary supplements are widely consumed for putative health benefits (e.g. cancer chemoprevention, beneficial effects on serum lipids associated with cardiovascular health, reduction of osteoporosis, relief of menopausal symptoms). However, studies of soy isoflavones in experimental animals suggest possible adverse effects as well (e.g. enhancement of reproductive organ cancer, modulation of endocrine function, anti-thyroid effects). This paper reviews the evidence in humans and animals for anti-thyroid effects of soy and its principal isoflavones, genistein and daidzein.
Keywords: Isoflavones; Thyroid peroxidase;
Thyroid gland function in ovariectomized ewes exposed to phytoestrogens by Andrzej Madej; Elisabeth Persson; Torbjörn Lundh; Yvonne Ridderstråle (281-287).
Phytoestrogens are by definition plant-derived substances that are able to activate the mammalian oestrogen receptors. We examined the possible effects of phytoestrogens on the secretion of thyroid hormones as well as on the immunoreactivity to oestrogen receptor alpha (ERα) in the thyroid glands of ovariectomized ewes. Eight ovariectomized ewes were fed 3.5 kg of 100% red clover silage for 14 days. Blood samples were collected before and on day 14 of exposure to phytoestrogens. After 5 months, four of the ewes were re-exposed to red clover silage as described above and the other four served as controls. Blood samples were collected as above. All ewes were slaughtered at the end of the experiment and the thyroid glands were weighed and examined for macroscopical changes. Tissue samples were taken for immunohistochemistry and image analysis. Ewes exposed to red clover silage had significantly higher plasma concentrations of total T3 and free T3 than ewes fed hay. The cross-section area of thyroid follicles tended to be larger in ewes fed red clover silage than in the control animals. ERα immunoreactivity was stronger in thyroid glands from ewes exposed to phytoestrogens than in ewes fed hay. In conclusion, daily ingestion of 81–95 mg phytoestrogens per kg body weight for 14 days stimulated secretion of thyroid hormones and tended to increase follicle size and ERα immunoreactivity of thyroid glands of ovariectomized ewes.
Mammalian phytoestrogens: enterodiol and enterolactone by Li-Quan Wang (289-309).
The mammalian phytoestrogens enterodiol (END) and enterolactone (ENL) are produced in the colon by the action of bacteria on the plant precursors matairesinol (MAT), secoisolariciresinol (SECO), their glycosides, and other precursors in the diet. Both END and ENL have been shown to possess weakly estrogenic and antiestrogenic activities, and it has been suggested that the high production of these antiestrogenic mammalian lignans in the gut may serve to protect against breast cancer in women and prostate cancer in men. Various in vitro experiments suggested END and ENL significantly inhibited the growth of human colon tumor cells, and the E2-induced proliferation of MCF-7 breast cancer cells was inhibited by ENL. The protective effects of mammalian lignans may be due to their ability to compete with E2 for the type II estrogen receptor, to induce sex hormone binding globulin (SHBG), to inhibit placental aromatase, and to act as antioxidants. This review mainly deals with the chemistry, quantitative analysis, biological properties and health effects of END and ENL.
Keywords: Phytoestrogens, mammalian; Enterodiol; Enterolactone;
Structural determinants of plant lignans for the formation of enterolactone in vivo by Niina M Saarinen; Annika Smeds; Sari I Mäkelä; Jenni Ämmälä; Kristo Hakala; Juha-Matti Pihlava; Eeva-Liisa Ryhänen; Rainer Sjöholm; Risto Santti (311-319).
The quantity of mammalian lignans enterolactone (ENL) and enterodiol (END) and of plant lignans secoisolariciresinol (SECO) and 7-hydroxymatairesinol (HMR) excreted in a 24-h rat urine sample was measured after a single p.o. dose of an equivalent quantity of secoisolariciresinol diglycoside (SDG), secoisolariciresinol (SECO), matairesinol (MR), 7-hydroxymatairesinol (HMR) and ENL. Plant lignans (SECO and HMR) were partially absorbed as such. The aglycone form of SECO was more efficiently converted into mammalian lignans END and ENL than the glycosylated form, SDG. Of plant lignans, MR produced the highest quantities of ENL: the quantity was over twofold compared with HMR or SDG. The majority of the animals, which had been given SECO, excreted higher quantities of END than ENL into urine, but ENL was the main lignan metabolite after SDG. The highest quantities of ENL in urine were measured after the administration of ENL as such. The (−)SECO isolated from Araucaria angustifolia was converted into (−)ENL only. The administration of (−)SDG, which was shown to produce (+)SECO, resulted in excretion of (+)ENL only and (−)HMR was converted into (−)ENL only. This confirmed that the absolute configurations at C8 and C8′ are not changed during the microbial metabolism. Whether the biological effects are enantiomer-specific, remains to be resolved.
Keywords: Enterolactone; Plant lignans;
Oxidative metabolites and genotoxic potential of mammalian and plant lignans in vitro by Heike B Niemeyer; Manfred Metzler (321-327).
Certain plant lignans, e.g. secoisolariciresinol and matairesinol, are converted by the intestinal microflora to the mammalian lignans enterodiol and enterolactone, which are associated with beneficial health effects in humans. The metabolism of both mammalian and plant lignans in animals and humans is poorly understood, and most studies so far have focused on the conjugation of these diphenolic compounds. However, recent studies have demonstrated that mammalian and plant lignans are good substrates for cytochrome P450-mediated reactions, leading to numerous products of aliphatic and aromatic hydroxylation with microsomes in vitro. The current knowledge of the oxidative metabolism of food-related lignans is briefly reviewed in this paper, including published as well as unpublished data from our laboratory. Moreover, data on the genotoxic potential of the mammalian and plant lignans, determined at various endpoints in cultured mammalian cells, are included in this review.
Author Index to vol. 777 (329-330).
Compound Index to Vol. 777 (331-332).