Phyto-oestrogens and Western diseases

Incidences of breast, colorectal and prostate cancer are high in the Western world compared to countries in Asia. We have postulated that the Western diet compared to the semivegetarian diet in some Asian countries may alter hormone production, metabolism or action at the cellular level by some biochemical mechanisms. Our interest has been focused on two groups of hormone-like diphenolic phyto-oestrogens of dietary origin, the lignans and isoflavonoids abundant in plasma of subjects living in areas with low cancer incidence. The precursors of the biologically active compounds detected in man are found in soybean products, whole-grain cereal food, seeds, and berries. The plant lignan and isoflavonoid glycosides are converted by intestinal bacteria to hormone-like compounds. The weakly oestrogenic diphenols formed influence sex-hormone production, metabolism and biological activity, intracellular enzymes, protein synthesis, growth factor action, malignant cell proliferation, differentiation, cell adhesion and angiogenesis in such a way as to make them strong candidates for a role as natural cancer-protective compounds. Their effect on some of the most important steroid biosynthetic enzymes may result in beneficial modulation of hormone concentrations and action in the cells preventing development of cancer. Owing to their oestrogenic activity they reduce hot flushes and vaginal dryness in postmenopausal women and may to some degree inhibit osteoporosis, but alone they may be insufficient for complete protection. Soy intake prevents oxidation of the low-density lipoproteins in vitro when isolated from soy-treated individuals and affect favourably plasma lipid concentrations. Animal experiments provide evidence suggesting that both lignans and isoflavonoids may prevent the development of cancer as well as atherosclerosis. However, in some of these experiments it has not been possible to separate the phyto-oestrogen effect from the effect of other components in the food. The isoflavonoids and lignans may play a significant inhibitory role in cancer development particularly in the promotional phase of the disease, but recent evidence points also to a role in the initiation stage of carcinogenesis. At present, however, no definite recommendations can be made as to the dietary amounts needed for prevention of disease. This review deals with all the above-mentioned aspects of phyto-oestrogens.

Case-control study of phyto-oestrogens and breast cancer

BACKGROUND

Phyto-oestrogens are a group of naturally occurring chemicals derived from plants; they have a structure similar to oestrogen, and form part of our diet. They also have potentially anticarcinogenic biological activity. We did a case-control study to assess the association between phyto-oestrogen intake (as measured by urinary excretion) and the risk of breast cancer.

METHODS

Women with newly diagnosed early breast cancer were interviewed by means of questionnaires, and a 72 h urine collection and blood sample were taken before any treatment started. Controls were randomly selected from the electoral roll after matching for age and area of residence. 144 pairs were included for analysis. The urine samples were assayed for the isoflavonic phyto-oestrogens daidzein, genistein, and equol, and the lignans enterodiol, enterolactone, and matairesinol.

FINDINGS

After adjustment for age at menarche, parity, alcohol intake, and total fat intake, high excretion of both equol and enterolactone was associated with a substantial reduction in breast-cancer risk, with significant trends through the quartiles: equol odds ratios were 1.00, 0.45 (95% CI 0.20, 1.02), 0.52 (0.23, 1.17), and 0.27 (0.10, 0.69)--trend p = 0.009--and enterolactone odds ratios were 1.00, 0.91 (0.41, 1.98), 0.65 (0.29, 1.44), 0.36 (0.15, 0.86)--trend p = 0.013. For most other phytoestrogens there was a reduction in risk, but it did not reach significance. Difficulties with the genistein assay precluded analysis of that substance.

INTERPRETATION

There is a substantial reduction in breast-cancer risk among women with a high intake (as measured by excretion) of phyto-oestrogens-particularly the isoflavonic phyto-oestrogen equol and the lignan enterolactone. These findings could be important in the prevention of breast cancer.

Antitumorigenic effect of a mammalian lignan precursor from flaxseed

Secoisolariciresinol diglycoside (SD), a mammalian lignan precursor found in high-fiber foods, was isolated from flaxseed and tested for effects on mammary tumorigenesis in rats fed a high-fat (20%) diet. Ingestion of purified SD at 1.5 mg/day for 20 weeks starting 1 week after treatment with the carcinogen dimethylbenzanthracene resulted in a 37% reduction (p < 0.05) in the number of tumors per tumor-bearing rat and a 46% reduction (p < 0.05) in the number of tumors per tumor-bearing rat and a 46% reduction (p < 0.05) in the number of tumors per number of rats in each group. Urinary mammalian lignan excretion significantly increased (p < 0.0001) with SD treatment, indicating the conversion of SD to mammalian lignans. No enlargement or gross abnormalities of the major organs were observed in the SD-treated rats. This study showed, for the first time, that SD has an antitumor effect when provided at the early promotion stage of tumorigenesis and may contribute to the health benefits of high-fiber foods.

Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis

Flaxseed, a rich source of mammalian lignan precursor secoisolariciresinol-diglycoside (S.D.) and alpha-linolenic acid (ALA), has been shown to be protective at the early promotion stage of carcinogenesis. The objective of this study was to determine whether supplementation with flaxseed, its lignan or oil fractions, beginning 13 weeks after carcinogen administration, would reduce the size of established mammary tumors (present at the start of treatment) and appearance of new tumors in rats. Dietary groups consisted of the basal diet (BD, 20% corn oil) alone or supplemented with a gavage of 2200 nmol/day S.D. [S.D., equal to level in 5% flaxseed (F)], 1.82% flaxseed oil (OIL, equal to level in 5% F) or 2.5% or 5% flaxseed (2.5% F and 5% F, respectively). After 7 weeks of treatment, established tumor volume was over 50% smaller in all treatment groups (OIL, 2.5% F, 5% F, P < 0.04; S.D., P < 0.08) while there was no change in the BD group. New tumor number and volume were lowest in the S.D. (P < 0.02) and 2.5% F (P < 0.07) groups. The combined established and new tumor volumes were smaller for the S.D., 2.5% F and 5% F groups (P < 0.02) compared to the OIL and BD groups. The high negative correlation (r = -0.997, P < 0.001) between established tumor volume and urinary mammalian lignan excretion in the BD, S.D., 2.5% F and 5% F groups indicates that the reduction in tumor size is due in part to the lignans derived from the S.D. in flaxseed. However, there was no relationship between new or total tumor development and urinary lignan levels. The effect of flaxseed oil may be related to its high ALA content. In conclusion, the S.D. in flaxseed appears to be beneficial throughout the promotional phase of carcinogenesis whereas the oil component is more effective at the stage when tumors have already been established.

Pilot study of urinary biomarkers of phytoestrogens, phthalates, and phenols in girls

BACKGROUND

Hormonally active environmental agents have been measured among U.S. children using exposure biomarkers in urine. However, little is known about their variation by race, age, sex, and geography, and no data exist for newly developed biomarkers.

OBJECTIVE

Our goal was to characterize relevant, prevalent exposures for a study of female pubertal development.

METHODS

In a pilot study among 90 girls from New York City, New York, Cincinnati, Ohio, and northern California, we measured 25 urinary analytes representing 22 separate agents from three chemical families: phytoestrogens, phthalates, and phenols. Exposures occur chiefly from the diet and from household or personal care products.

RESULTS

Participants represented four racial/ethnic groups (Asian, black, Hispanic, white), with mean age of 7.77 years. Most analytes were detectable in > 94% of samples. The highest median concentrations for individual analytes in each family were for enterolactone (298 microg/L), monoethylphthalate (MEP; 83.2 microg/L), and benzophenone-3 (BP3; 14.7 microg/L). Few or no data have been reported previously for four metabolites: mono(2-ethyl-5-carboxypentyl) phthalate, tridosan, bisphenol A (BPA), and BP3; these were detected in 67-100% of samples with medians of 1.8-53.2 microg/L. After multivariate adjustment, two analytes, enterolactone and BPA, were higher among girls with body mass index < 85th reference percentile than those at or above the 85th percentile. Three phthalate metabolites differed by race/ethnicity [MEP, mono(2-ethylhexyl) phthalate, and mono-3-carboxypropylphthalate].

CONCLUSIONS

A wide spectrum of hormonally active exposure biomarkers were detectable and variable among young girls, with high maximal concentrations (> 1,000 microg/L) found for several analytes. They varied by characteristics that may be relevant to development.

Metabolites of dietary (soya) isoflavones in human urine

This study was undertaken to better understand the metabolic fate of dietary isoflavones in humans. Twelve volunteers were challenged with soya flour and urinary diphenol levels were then determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The presence of previously described urinary diphenols was confirmed, i.e. the isoflavones, daidzein and genistein; the isoflavonoid metabolites, equol, dihydrodaidzein (Int-O-D), O-desmethyl-angolensin (O-Dma); the lignan, enterolactone. Diphenols detected for the first time were the isoflavone, glycitein and five novel isoflavonoid metabolites which are tentatively identified as 6'-hydroxy-O-desmethylangolensin (6' OH-O-Dma), dihydrogenistein (Int-O-G), dehydro-O-desmethylangolensin (dehydro-O-Dma) and two isomers of tetrahydrodaidzein. Urinary excretion rates of the three isoflavones (daidzein, genistein, glycitein) over a 3-day period following soya challenge showed moderate variation (4x, 6x and 12x, respectively) between the 12 individuals suggesting some individual variabilities in ability to deconjugate and to absorb dietary isoflavones. However, urinary excretion rates of each of three major isoflavonoid metabolites (equol, O-Dma, 6' OH-O-Dma) showed more marked variation (922x, 17x, 15x, respectively); while some of this variability may reflect varying individual ability to ferment dietary isoflavones per se, an inverse relationship was found between urinary levels of equol and both O-Dma and 6' OH-O-Dma suggesting individual variability in the preferred metabolic pathways of dietary isoflavones.

The variable metabolic response to dietary isoflavones in humans

The aim of this study was to better understand the metabolic fate of dietary estrogenic isoflavones in humans. Twelve volunteers were challenged with soya flour and urinary levels of the isoflavones daidzein (Da), genistein (Gen), and glycitein (Gly), and the isoflavonoid metabolites equol (Eq) and O-desmethylangolensin (O-Dma) determined by GC and GC-MS. Prior to challenge, Da, Gen, and Gly were present in the urine of all participants at low levels and Eq and O-Dma were present in 9/12 and 10/12 participants, respectively. Urinary levels of all five diphenols were increased in each individual on the day following challenge, returning to approximately prechallenge levels on the second or third day post-challenge. Mean post-challenge peak levels of the five diphenols compared with pre-challenge levels were Da (4x), Gen (8x), Gly (5x), Eq (45x), and O-Dma (66x). However, there was considerable individual variation in this metabolic response with peak levels of Eq showing the highest variation (1527x). An inverse relationship between Eq and O-Dma excretion was also found post-challenge suggesting individual variability in the preferred metabolic pathways of dietary isoflavones.

The influence of flaxseed and lignans on colon carcinogenesis and beta-glucuronidase activity

Flaxseed, the richest source of mammalian lignan precursors, such as secoisolariciresinol diglycoside (SD), has been shown over the short term to decrease some early markers of colon cancer risk. This study determined whether over the long term flaxseed still exerts a colon cancer protective effect, whether its effect may, in part, be due to its high content of SD and whether any change in beta-glucuronidase activity plays a role in the protective effect. Six groups of male Sprague-Dawley rats were fed for 100 days either a basal high fat (20%) diet (BD), BD supplemented with 2.5 or 5% flaxseed or 2.5 or 5% defatted flaxseed (equivalent to the respective flaxseed diets) or BD with a daily gavage of 1.5 mg SD. All rats were injected with a single dose of azoxymethane (15 mg/kg body wt) 1 week prior to commencing the dietary treatments. Urinary lignan excretion, which is an indicator of mammalian lignan production, was significantly increased in the flaxseed and defatted flaxseed groups. The total activity of cecal beta-glucuronidase was significantly increased in a dose-dependent manner by the flaxseed and defatted flaxseed diet groups. Compared with the control the number of aberrant crypts per focus was significantly reduced in the distal colon of the treated rats. Four microadenomas and two polyps were observed in the control group, but not in the treated groups. The total activity of beta-glucuronidase was positively correlated with total urinary lignan excretion and negatively with the total number of aberrant crypts and the total number of aberrant crypt foci in the distal colon. There were no significant differences between the flaxseed and the corresponding defatted flaxseed groups. It is concluded that flaxseed has a colon cancer protective effect, that it is due, in part, to SD and that the protective effect of flaxseed is associated with increased beta-glucuronidase activity.

Phytoestrogens and breast cancer risk. Review of the epidemiological evidence

Phytoestrogens are natural plant substances. The three main classes are isoflavones, coumestans, and lignans. Phytoestrogens have anticarcinogenic potential, but they have also significant estrogenic properties. For an evaluation of the effect of phytoestrogens on breast cancer risk we reviewed the analytical epidemiological data. A total of 18 studies were included. Up to now, there are 13 studies that have assessed the direct relation between the individual dietary intake of soy products and the risk of breast cancer. Overall, results do not show protective effects, with the exception maybe for women who consume phytoestrogens at adolescence or at very high doses. Only four of these 13 studies are prospective, and none of them found statistically significant breast cancer reductions. Four studies assessed urinary isoflavones excretion in relation to breast cancer. Three of these are case control studies, where excretion was measured after breast cancer occurrence and thus seriously limiting causal interpretation of the results. The only prospective study with urinary measurements before breast cancer occurrence was done in a Dutch postmenopausal population and showed a non-significant breast cancer risk reduction for high excretion. Three studies measured enterolactone (lignan): two case control studies reported a preventive effect on breast cancer risk, but the only prospective study did not . In conclusion, few prospective studies (n = 5) were done to assess the effects of phytoestrogens on breast cancer risk. None of them found protective effects. However, these prospective studies did not focus on 'age at consumption', which seems to be important based on results from dietary case control studies done so far.

Lignan and isoflavonoid conjugates in human urine

Lignans and isoflavonoids are two groups of diphenolic phytoestrogens of plant origin which have gained increasing interest because of their possible cancer protective properties. High excretion of these compounds occur in populations at low risk of breast, prostate and colon cancer consuming either high amounts of whole-grain (lignans and some isoflavonoids) or soy products (isoflavonoids and some lignans). We determined the pattern of conjugation of the phytoestrogens in four urine samples from vegetarian or semivegetarian women and in two samples from men. Seven compounds were investigated: enterodiol, enterolactone, matairesinol, diadzein, equol, genistein and O-desmethylangolensin. The fractions quantified are the free fraction, mono- and disulfate, as well as the mono-, di- and sulfoglucuronide fractions. For the fractionation and purification we used ion-exchange chromatography and the determination of the concentrations of each compound in all fractions was done by isotope dilution gas chromatography-mass spectrometry (GLC-MS) using deuterated internal standards of all diphenols. More than 60% of all compounds determined, occurred in the monoglucuronide fraction. Daidzein, enterodiol and equol are excreted to a relatively high extent as sulfoglucuronides and genistein as diglucuronide. We conclude that the general pattern of lignan and isoflavonoid conjugates in urine is similar to that of endogenous estrogens.

Hydroxymatairesinol, a novel enterolactone precursor with antitumor properties from coniferous tree (Picea abies)

The potential for the extraction of the plant lignan hydroxymatairesinol (HMR) in large scale from Norway spruce (Picea abies) has given us the opportunity to study the metabolism and biological actions of HMR in animals. HMR, the most abundant single component of spruce lignans, was metabolized to enterolactone (ENL) as the major metabolite in rats after oral administration. The amounts of urinary ENL increased with the dose of HMR (from 3 to 50 mg/kg), and only minor amounts of unmetabolized HMR isomers and other lignans were found in urine. HMR (15 mg/kg body wt po) given for 51 days decreased the number of growing tumors and increased the proportion of regressing and stabilized tumors in the rat dimethylbenz[a]anthracene-induced mammary tumor model. HMR (50 mg/kg body wt) did not exert estrogenic or antiestrogenic activity in the uterine growth test in immature rats. HMR also showed no antiandrogenic responses in the growth of accessory sex glands in adult male rats. Neither ENL nor enterodiol showed estrogenic or antiestrogenic activity via a classical alpha- or beta-type estrogen receptor-mediated pathway in vitro at < 1.0 microM. HMR was an effective antioxidant in vitro.

Urinary isoflavonoid phytoestrogen and lignan excretion after consumption of fermented and unfermented soy products

OBJECTIVE

To compare the effects of consumption of fermented and unfermented soy products on excretion of urinary isoflavonoid phytoestrogens and lignans in healthy men.

DESIGN

A randomized, crossover trial consisting of two 9-day feeding periods following 5 days of baseline data collection.

SUBJECTS

Healthy men, aged 20 to 40 years, were recruited from the University of Minnesota Twin Cities community. Of the 22 subjects who began the study, 17 completed all feeding periods.

INTERVENTIONS

Fermented soy product (112 g tempeh) or unfermented soy (125 g soybean pieces) was consumed during each controlled feeding period.

MAIN OUTCOME MEASURE

Urine samples collected while subjects consumed their habitual diets and on the last 3 days of each feeding period were analyzed for isoflavonoid and lignan content by isotope dilution gas chromatography-mass spectrometry.

STATISTICAL ANALYSIS PERFORMED

Comparisons of isoflavonoid and lignan excretion were analyzed using the general linear model procedure. Orthogonal contrasts were used to determine treatment differences of interest.

RESULTS

Urinary excretion of isoflavonoids (equol, O-desmethylangolensin [O-DMA], daidzein, genistein) was higher and excretion of lignans (enterodiol, enterolactone) was lower when subjects consumed soy-supplemented diets than when they consumed their habitual diets (P < .05). Urinary isoflavonoid excretion and lignan excretion were similar when subjects consumed tempeh and soybean pieces diets; however, recovery of daidzein and genistein was significantly higher when subjects consumed the tempeh diet than when they consumed the soybean pieces diet (P < .002). When fed soy, 5 of 17 subjects excreted high amounts of equol. These five subjects tended to excrete less O-DMA and daidzein than the 12 subjects who excreted low amounts of equol (P < .06).

CONCLUSIONS

Fermentation of soy decreased the isoflavone content of the product fed but increased the urinary isoflavonoid recovery. This finding suggests that fermentation increases availability of isoflavones in soy.

Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer

PURPOSE

Flaxseed, the richest source of mammalian lignan precursors, has previously been shown to reduce the growth of tumors in rats. This study examined, in a randomized double-blind placebo-controlled clinical trial, the effects of dietary flaxseed on tumor biological markers and urinary lignan excretion in postmenopausal patients with newly diagnosed breast cancer.

EXPERIMENTAL DESIGN

Patients were randomized to daily intake of either a 25 g flaxseed-containing muffin (n = 19) or a control (placebo) muffin (n = 13). At the time of diagnosis and again at definitive surgery, tumor tissue was analyzed for the rate of tumor cell proliferation (Ki-67 labeling index, primary end point), apoptosis, c-erbB2 expression, and estrogen and progesterone receptor levels. Twenty-four-hour urine samples were analyzed for lignans, and 3-day diet records were evaluated for macronutrient and caloric intake. Mean treatment times were 39 and 32 days in the placebo and flaxseed groups, respectively.

RESULTS

Reductions in Ki-67 labeling index (34.2%; P = 0.001) and in c-erbB2 expression (71.0%; P = 0.003) and an increase in apoptosis (30.7%; P = 0.007) were observed in the flaxseed, but not in the placebo group. No significant differences in caloric and macronutrient intake were seen between groups and between pre- and posttreatment periods. A significant increase in mean urinary lignan excretion was observed in the flaxseed group (1,300%; P < 0.01) compared with placebo controls. The total intake of flaxseed was correlated with changes in c-erbB2 score (r = -0.373; P = 0.036) and apoptotic index (r = 0.495; P < 0.004).

CONCLUSION

Dietary flaxseed has the potential to reduce tumor growth in patients with breast cancer.

Human metabolism of mammalian lignan precursors in raw and processed flaxseed

BACKGROUND

The mammalian lignans enterolactone and enterodiol are produced in the colon by the action of bacteria on the plant precursor secoisolariciresinol diglycoside, which is found in high concentrations in flaxseed.

OBJECTIVE

Two experiments were conducted to determine 1) whether there is a dose response in urinary lignan excretion with increasing flaxseed intake, 2) whether flaxseed processing affects lignan excretion, 3) peak plasma lignan concentrations, and 4) plasma lignan concentrations after chronic supplementation.

DESIGN

Nine healthy young women supplemented their diets with 5, 15, or 25 g raw or 25 g processed (muffin or bread) flaxseed for 7 d during the follicular phase of their menstrual cycles. Twenty-four-hour urine samples were collected at baseline and on the final day of supplementation. As an adjunct to the 25-g-flaxseed arm, subjects consumed the supplement for an additional day and blood and urine samples were collected at specific intervals. All blood and urine samples were analyzed for enterolactone and enterodiol by gas chromatography-mass spectroscopy.

RESULTS

A dose-dependent urinary lignan response to raw flaxseed was observed (r = 0.72, P < 0.001). The processing of flaxseed as a muffin or bread did not affect the quantity of lignan excretion. Plasma lignan concentrations were greater (P < or = 0.05) than baseline by 9 h after flaxseed ingestion (29.35+/-3.69 and 51.75+/-7.49 nmol/L, respectively). The total plasma area under the curve was higher on the eighth than on the first day (1840.15+/-343.02 and 1027.15+/-95.71 nmol x h/L, respectively).

CONCLUSION

Mammalian lignan production from flaxseed precursors is dependent on time and dose but not on processing.

Effects of dietary phytoestrogens in postmenopausal women

The aim of this study was to test the hypothesis that increased dietary intake of phytoestrogens reduces the health impact of the menopause. To test this hypothesis, a double-blind, randomized, entry-exit, cross-over study was conducted to assess the effects of three dietary manipulations--soy and linseed diets (high in phytoestrogens) and a wheat diet (low in phytoestrogens). Postmenopausal women were recruited and randomly assigned to one of the three dietary regimens. Urinary phytoestrogen concentrations, hot flush rate, vaginal smears, bone mineral density and bone mineral content were assessed for two 12-week periods. Comparative analysis showed no significant differences, but, when analyzed separately, groups consuming high phytoestrogen diets had between 10 and 30 times higher urinary excretion of phytoestrogens compared to those consuming the low phytoestrogen diet (p < 0.01). Study participants consuming soy, linseed and wheat diets had a 22% (not significant, n.s.), 41% (p < 0.009) and 51% (p < 0.001) reduction in hot flush rate; a 103% (p < 0.04), 5.5% (n.s.) and 11% (n.s.) increase in vaginal cytology maturation index; and a 5.2% (p < 0.04), 5.2% (n.s.) and 3.8% (n.s.) increase in bone mineral content, respectively. No changes were detected in bone mineral density. The differential effects of high phytoestrogen dietary manipulations on outcomes may represent tissue-specific responses to isoflavones and lignans contained in soy and linseed, respectively. Whilst health outcome measures were not significantly different between groups, the data obtained from separate analysis suggest that phytoestrogens in soy and linseed may be of use in ameliorating some of the symptoms of menopause. Furthermore, the significant decrease in hot flush rate in the wheat group cannot be attributable to phytoestrogens measured in this study. Due to subject variability, larger studies are still needed to evaluate population benefit.

Identification of isoflavone metabolites dihydrodaidzein, dihydrogenistein, 6'-OH-O-dma, and cis-4-OH-equol in human urine by gas chromatography-mass spectroscopy using authentic reference compounds

The metabolic products of daidzein and genistein, the principal isoflavones of soy, were examined. Six volunteers included soy into their normal diet for a 2-week period and urine samples were analyzed before and after soy consumption. Isolation and characterization of the urinary metabolites were carried out with absorption chromatography on Sephadex LH-20 and gas chromatography-electron ionization mass spectrometry (GC-EIMS). The structures of the isoflavones isolated were confirmed by using authentic reference compounds. Dihydrogenistein, 6'-OH-O-desmethylangolensin, and cis-4-OH-equol were identified, in addition to known isoflavonoids daidzein, genistein, glycitein, and the known metabolites equol, O-desmethylangolensin, and dihydrodaidzein, by comparing the retention times and the spectra of the urinary compounds with those of the synthesized reference standards. The mammalian lignans enterolactone and enterodiol were also identified. Derivatization of the isoflavones for GC-MS was examined by comparing two silylating reagents, N, O-bis-(trimethylsilyl)-trifluoroacetamide (BSTFA) and pyridine:hexamethyldisilazan:trimethylchlorosilane (QSM), both used for the derivatization of these compounds. The silylation experiments revealed significant differences in the compositions of the derivatization products. Some corrections were made concerning the earlier published data of dihydrogenistein and 6'-OH-O-dma.

Sesamin is one of the major precursors of mammalian lignans in sesame seed (Sesamum indicum) as observed in vitro and in rats

Plant lignans occur in many foods, with flaxseed presently recognized as the richest source. Some plant lignans can be converted by intestinal microbiota to the mammalian lignans, enterodiol and enterolactone, which may have protective effects against hormone-related diseases such as breast cancer. This study determined whether plant lignans in sesame seed, particularly sesamin, could be metabolized to the mammalian lignans. The total plant lignan concentration in sesame seed (2180 micromol/100 g) was higher than that in flaxseed (820 micromol/100 g). In vitro fermentation with human fecal inoculum showed conversion of sesamin to the mammalian lignans, although at a lower rate (1.1%) compared with that of secoisolariciresinol diglucoside (57.2%). However, when fed to female Sprague-Dawley rats for 10 d, sesamin (15 mg/kg body weight) and a 10% sesame seed diet resulted in greater (P < 0.05) urinary mammalian lignan excretion (3.2 and 11.2 micromol/d, respectively), than the control (< 0.05 micromol/d). We conclude that sesame seed is a rich source of mammalian lignan precursors and sesamin is one of them. From intermediate metabolites of sesamin identified in rat urine by GC-MS, a tentative metabolic pathway of sesamin to mammalian lignans is suggested.

Extraction and quantification of lignan phytoestrogens in food and human samples

Dietary phytoestrogens have a number of biological effects, including endocrine disruption, antioxidant potential, and protein tyrosine kinase inhibition. Secoisolariciresinol, matairesinol, and shonanin are lignan phytoestrogens found in foodstuffs, especially flaxseed. Normally they are glycosidically linked to carbohydrates and in the large intestine are deconjugated from the carbohydrate portion by bacteria. The aglycone lignans can be further modified to form the mammalian phytoestrogens enterodiol, enterolactone, and enterofuran, which are absorbed into the body and excreted in urine. To assess the health implications of phytoestrogens in general populations, knowledge of the quantity in the foods eaten is necessary. This article describes a simple preparative procedure for the assay of secoisolariciresinol, matairesinol, and shonanin in foodstuffs after hydrolytic removal of any conjugated carbohydrate. The difficulties in the practical application of the assay procedure are illustrated and discussed. Analytical results indicating the concentration of secoisolariciresinol, matairesinol, and shonanin in a number of foodstuffs are presented. Also, the mass spectral data of a putative mammalian phytoestrogen, called enterofuran, identified in urine are presented.

Urinary lignan and isoflavonoid excretion in premenopausal women consuming flaxseed powder

Lignans and isoflavonoid phytoestrogens, produced from plant precursors by colonic bacteria, may protect against certain cancers. We examined the effects of flaxseed consumption on urinary lignans and isoflavonoids. Eighteen women consumed their usual omnivorous diets for three menstrual cycles and their usual diets supplemented with flaxseed powder (10 g/d) for three cycles in a randomized crossover design. Three-day urine samples from follicular and luteal phases were analyzed for lignans and isoflavonoids by isotope-dilution gas chromatography--mass spectrometry. Excretion of the lignans enterodiol and enterolactone increased with flaxseed from 1.09 +/- 1.08 and 3.16 +/- 1.47 to 19.48 +/- 1.10 and 27.79 +/- 1.50 mumol/d, respectively (P < 0.0002). Enterodiol and enterolactone excretion varied among subjects in response to flaxseed (3- to 285-fold increase). There were no differences in excretion of isoflavonoids (daidzein, genistein, equol, and O-desmethylangolensin) or the lignan matairesinol with flaxseed. Excretion was not altered by phase of menstrual cycle or duration of flaxseed consumption.

Urinary lignan and isoflavonoid excretion in men and women consuming vegetable and soy diets

Urinary lignan and isoflavonoid excretion were examined in 11 men and 9 women consuming four nine-day controlled experimental diets: basal (vegetable free), carotenoid vegetable (carrot and spinach), cruciferous vegetable (broccoli and cauliflower), and soy (tofu and textured vegetable protein product). Three-day urine collections (Days 7-9) were analyzed for lignans and isoflavonoids with use of isotope-dilution gas chromatography-mass spectrometry. Urinary excretion of the lignans enterodiol and enterolactone was higher during the carotenoid and cruciferous vegetable diets than during the basal diet (p = 0.0001), suggesting that these vegetables may provide a source of mammalian lignan precursors. Urinary excretion of the isoflavonoids equol, O-desmethylangolensin, daidzein, and genistein was higher when subjects consumed soy diets than when they consumed the other test diets (p < 0.02). Gender differences in lignan excretion were observed. Men excreted more enterolactone (p = 0.006) and less enterodiol (p = 0.013) than women, implying a gender difference in colonic bacterial metabolism of lignans. There was no effect of gender on isoflavonoid excretion.

Dietary lignins are precursors of mammalian lignans in rats

The mammalian lignans enterolactone (ENL) and enterodiol, commonly found in human plasma and urine, are phytoestrogens that may contribute to the prevention of breast cancer and coronary heart disease. They are formed by the conversion of dietary precursors such as secoisolariciresinol and matairesinol lignans by the colonic microflora. The identification of lignins, cell-wall polymers structurally related to lignans, as precursors of mammalian lignans is reported here for the first time. In study 1, rats were fed rye or wheat bran (15% diet) for 5 d. Untreated brans and brans extracted with solvents to remove lignans were compared. ENL was estimated in urine samples collected for 24 h by time-resolved fluoroimmunoassay. ENL urinary excretion was reduced from 18.6 to 5.3 nmol/d (n=8; P<0.001) when lignans were removed from rye bran and from 30.5 to 6.2 nmol/d (P<0.001) when they were removed from wheat bran. These results suggest that lignins, embedded in the cell wall and retained in the bran during solvent extraction, account for 26-32% of the ENL formed from cereal brans. In study 2, rats were fed a deuterated synthetic lignin (0.2% diet) together with wheat bran (15%) for 3 d. The detection of deuterated ENL by LC-tandem MS in urine (20 nmol/d) clearly confirms the conversion of lignin into mammalian lignans. More research is warranted to determine the bioavailability of lignins in the human diet.

The effect of a lignan complex isolated from flaxseed on inflammation markers in healthy postmenopausal women

BACKGROUND AND AIM

Plant lignans are metabolised by the colonic micro-flora to the mammalian lignans enterodiol and enterolactone, which are hypothesized to be cardioprotective. The aim of this study was to investigate the effects of a plant lignan complex isolated from flaxseed, providing 500 mg/d of secoisolariciresinol diglucoside, on inflammatory markers.

METHODS AND RESULTS

Healthy postmenopausal women (n=22) completed a randomised double-blind, placebo-controlled crossover study. Women consumed daily a low-fat muffin, with or without a lignan complex, for 6 weeks, separated by a 6-week washout period. A significant difference of approximately 15% (P=0.028) was observed for C-reactive protein (CRP) concentration between the lignan complex intervention period and placebo period. CRP concentrations (median; 25th, 75th percentiles) were 0.88 (0.63, 2.05) mg/L at baseline and 0.92 (0.59, 1.49) mg/L after the lignan complex intervention period compared with 0.80 (0.62, 1.62) mg/L at baseline and 1.10 (0.72, 1.62) mg/L after placebo. No significant differences in interleukin-6, tumor necrosis factor-alpha, soluble intracellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and monocyte chemoattractant protein-1 were found between the lignan complex intervention period and placebo period.

CONCLUSION

Daily consumption for 6 week of a low-fat muffin enriched with a lignan complex may reduce CRP concentrations compared to a low-fat muffin with no lignans added.

Quantification of isoflavones and lignans in urine using gas chromatography/mass spectrometry

Phytoestrogens (isoflavones and lignans) are of increasing interest due to their potential to prevent certain types of complex diseases. However, epidemiological evidence is needed on the levels of phytoestrogens and their metabolites in foods and biological fluids in relation to risk of these diseases. We report an assay for phytoestrogens which is sensitive, accurate, and uses low volumes of sample. Suitable for epidemiological studies, the assay consists of a simple sample preparation procedure and has been developed for the analysis of five isoflavones (daidzein, O-desmethylangolensin, equol, genistein, and glycitein) and two lignans (enterodiol and enterolactone), which requires only 200 microl of urine and utilizes one solid-phase extraction stage for sample preparation prior to derivatization for GC/MS analysis. Limits of detection were in the region 1.2 ng/ml (enterodiol) to 5.3ng/ml (enterolactone) and the method performed well in the UK Government's Food Standards Agency-sponsored quality assurance scheme for phytoestrogens. For the first time, average levels of all the above phytoestrogens were measured in samples of urine collected from a free living population sample of women. Results show a large range in both the amount and the type of phytoestrogens excreted.

Vegetables, fruits, and legumes: effect on urinary isoflavonoid phytoestrogen and lignan excretion

OBJECTIVE

To compare the effect of vegetable, fruit, and legume consumption on urinary isoflavonoid phytoestrogen and lignan excretion.

DESIGN

After 4 days of data collection, during which subjects consumed their habitual diets, subjects were randomly placed on four 9-day controlled experimental diets with each subject receiving each diet in a random order.

SUBJECTS

Seven men and three women, aged 20 to 35 years, were recruited from the University of Minnesota Twin Cities community.

INTERVENTIONS

All subjects consumed four experimental diets in an assigned random order: a controlled basal diet, a legume/allium diet (containing garbanzo beans, garlic, and onions), and diets low or high in vegetables and fruits (containing apples, pears, potatoes, and carrots).

MAIN OUTCOME MEASURES

Urine samples that were collected while subjects consumed their habitual diets and during the last 3 days of each feeding period were analyzed for isoflavonoid and lignan content using isotope dilution gas chromatography-mass spectrometry.

STATISTICAL ANALYSIS PERFORMED

The effect of vegetable and fruit intake on urinary isoflavonoid and lignan excretion was analyzed using the general linear model procedure. Post hoc comparisons were made using Duncan's multiple range test.

RESULTS

Subjects excreted more of the lignan enterodiol on the high vegetable/fruit diet compared with the basal and legume/allium diets (P = .03); more of the isoflavonoids O-desmethylangolensin (O-DMA), genistein, and sum of isoflavonoids on the legume/allium diet compared with the other controlled diets (P < .05); and more of the isoflavan equol on the basal and legume/allium diets compared with the high vegetable/fruit diet (P < .01). Subjects who excreted higher levels of equol on the basal and legume/allium diets also consumed more of the milk-based pudding provided as part of the controlled diets.

CONCLUSIONS

Urinary lignan and isoflavonoid excretion changed in response to alterations in vegetable, fruit, and legume intake under controlled dietary conditions.