Time-resolved fluoroimmunoassay for plasma enterolactone

We present a method for the determination of the lignan enterolactone in plasma (serum). This compound, produced by intestinal bacteria from matairesinol and secoisolariciresinol in fiber-rich food, is a biomarker related to the intake of a healthy diet. The method is based on time-resolved fluoroimmunoassay using a europium chelate as a label. After synthesis of 5'-O-carboxymethoxyenterolactone the compound is coupled to bovine serum albumin and then used as antigen in immunization of rabbits. The tracer with the europium chelate is synthesized using the same 5'-derivative of enterolactone. After enzymatic hydrolysis and ether extraction the immunoassay is carried out using the VICTOR 1420 multilabel counter (Wallac Oy, Turku, Finland). No antiserum cross-reactivity with available lignans, isoflavonoids, or flavonoids could be detected. The intraassay and interassay coefficients of variation at different concentrations vary 4.6-6.0 and 5.5-9.9, respectively. The working range of the assay is 1.5-540 nmol/liter. We measured enterolactone in serum/plasma of 224 Finnish subjects: 98.8% of the subjects had values <100 nmol/liter, 38.0% had 20-39.9 nmol/liter, and 34.4% had <20 nmol/liter.

Phytoestrogens and inhibition of angiogenesis

The consumption of a plant-based diet can prevent the development and progression of chronic diseases associated with extensive neovascularization, including the progression and growth of solid malignant tumours. We have previously shown that the plant-derived isoflavonoid genistein is a potent inhibitor of cell proliferation and in vitro angiogenesis. Moreover, the concentration of genistein in the urine of subjects consuming a plant-based diet is 30-fold higher than that in subjects consuming a traditional Western diet. We have also reported that certain structurally related flavonoids are more potent inhibitors than genistein. Indeed, 3-hydroxyflavone, 3',4'-dihydroxyflavone, 2',3'-dihydroxyflavone, fisetin, apigenin and luteolin inhibit the proliferation of normal and tumour cells as well as in vitro angiogenesis at half-maximal concentrations in the lower micromolar range. The wide distribution of isoflavonoids and flavonoids in the plant kingdom, together with their anti-angiogenic and anti-mitotic properties, suggest that these phytoestrogens may contribute to the preventive effect of a plant-based diet on chronic diseases, including solid tumours.

Pharmacokinetics of soybean isoflavones in plasma, urine and feces of men after ingestion of 60 g baked soybean powder (kinako)

To take advantage of the various pharmacologic activities of soy bean isoflavones, more detailed studies of the absorption and excretion rates of these compounds in humans and subsequent evaluation of their bioavailabilities are required. We conducted a pharmacokinetic study of soybean isoflavones in seven healthy male volunteers. After ingestion of 60 g of kinako (baked soybean powder, containing 103 micromol daidzein and 112 micromol genistein), changes of the isoflavone and metabolite concentrations in plasma, urine and feces were measured by gas chromatography-mass spectrometry. The plasma concentration of genistein increased after 2 h and reached its highest value of 2.44 +/- 0.65 micromol/L 6 h later. The plasma concentration of daidzein peaked at 1.56 +/- 0.34 micromol/L at the same time, but it was always lower than that of genistein. Peak plasma concentration of O-desmethylangolensin (O-DMA) and equol appeared after the daidzein peak in four and two subjects, respectively. In contrast with plasma, daidzein was the main component in urine. Urinary daidzein excretion started to increase shortly after the rise in its plasma concentration and reached 2.4 micromol/h 8 h after ingestion of kinako. Genistein excretion in urine paralleled that of daidzein, but the value at 6 h was about half (1.1 micromol/h). The majority of ingested isoflavones after ingestion of kinako were recovered on d 2 or 3 in the feces. Total recovery of daidzein, O-DMA and equol from urine and feces was 54.7%, calculated from daidzein intake; 20.1% of administered genistein was recovered as genistein. The half-lives of plasma genistein and daidzein were 8.36 and 5.79 h, respectively. The individual plasma and urinary concentrations of equol and O-DMA were quite variable; subjects were classified as high and low metabolizers. The high plasma concentration of isoflavones for at least several hours after a single ingestion of soy protein suggests that these compounds may interact with macromolecules and have biological effects.

Effect of soybean phytoestrogen intake on low density lipoprotein oxidation resistance

The oxidation of low density lipoproteins (LDLs) is thought to take place in the arterial intima when the particles have become isolated from circulating water-soluble antioxidants. We hypothesized that isoflavonoid antioxidants derived from soy could be incorporated into lipoproteins and possibly could protect them against oxidation, which is regarded as atherogenic. Six healthy volunteers received 3 soy bars [containing the isoflavonoid antioxidants genistein (12 mg) and daidzein (7 mg)] daily for 2 weeks. LDLs were isolated from blood drawn at the the end of a 2-week dietary baseline period, after 2 weeks on soy, and after discontinuation of soy. Large increases in plasma isoflavonoid levels occurred during soy feeding, but only minute amounts were stably associated with lipoproteins (less than 1% of plasma isoflavonoids in the LDL fraction). The LDLs were subjected to copper-mediated oxidation in vitro. Compared with off soy values, lag phases of LDL oxidation curves were prolonged by a mean of 20 min (P < 0.02) during soy intake, indicating a reduced susceptibility to oxidation. The results suggest that intake of soy-derived antioxidants, such as genistein and daidzein, may provide protection against oxidative modification of LDL. As only very small amounts of these substances were detected in purified LDL, modified LDL particles may have been produced in vivo by circulating isoflavonoids promoting resistance to oxidation ex vivo.

Radioimmunoassay of free genistein in human serum

Two radioimmunoassay (RIA) systems for genistein have been established, based on polyclonal antibodies against genistein-4'-O-(carboxymethyl)ether-bovine serum albumin and genistein-7-O-(carboxymethyl)ether-bovine serum albumin conjugates. The sensitivities of assays were 4.44 and 10.4 fmol (1.2 and 2.8 pg)/tube, respectively, the intraassay coefficients of variation ranged from 3.54 to 9.30%, the interassay C.V. varied from 6.72 to 19.7%, depending on the type of method and on genistein concentration. The cross-reactivities with other chemically related compounds (with exception of genistein derivatives at the position used for construction of the immunogen) were 5.5 and 6.1% for daidzein and 3.9 and 0.04% for formononetin in RIAs using reagents prepared through positions 4'- and 7- of genistein, respectively. The method was used for measurement of genistein levels in 26 omnivore subjects and in three volunteers after consumption of a meal prepared from 125 g of cooked whole soybeans. The values obtained in ether extracts from human sera were almost identical for both RIA systems, indicating that both RIAs measure the same entity.

Synthesis of novel mammalian metabolites of the isoflavonoid phytoestrogens daidzein and genistein

The synthesis of novel mammalian metabolites of dietary isoflavones, dihydrodaidzein (4',7-dihydroxyisoflavanone) 7, dihydrogenistein (4',5,7-trihydroxyisoflavanone) 9, 6'-hydroxy-O-demethylangolensin [1-(2,4,6-trihydroxyphenyl)-2-(4-hydroxyphenyl)propan-1-one] 10, and cis- and trans-4',7-dihydroxyisoflavan-4-ols 11, 12 is described, and their characteristics by physical and chemical constants given for the first time.

Lignan and isoflavonoid concentrations in tea and coffee

Tea is a beverage consumed widely throughout the world. The existence in tea of chemopreventing compounds possessing antimutagenic, anticarcinogenic and antioxidative properties has been reported. High intakes of tea and foods containing flavonoids have recently been shown to be negatively correlated to the occurrence of CHD. However, tea may contain other compounds with similar activities. Using a new gas chromatographic-mass spectrometric method we measured lignans and isoflavonoids in samples of twenty commercial teas (black, green and red varieties) and, for comparison, six coffees. Both unbrewed and brewed tea were investigated. The analysis of the teas yielded relatively high levels of the lignans secoisolariciresinol (5.6-28.9 mg/kg; 15.9-81.9 mumol/kg) and matairesinol (0.56-4.13 mg/kg; 1.6-11.5 mumol/kg) but only low levels of isoflavonoids. Because the plant lignans, as well as their mammalian metabolites enterolactone and enterodiol, have antioxidative properties and these mammalian lignans occur in high concentrations in plasma, we hypothesize that lignan polyphenols may contribute to the protective effect of tea on CHD.

Identification of isoflavonoids in beer

The isoflavonoids, genistein (4',5,7-trihydroxyisoflavone), biochanin A (5,7-dihydroxy-4'-methoxyisoflavone), daidzein (4',7-dihydroxyisoflavone), and formononetin (7-hydroxy-4'-methoxyisoflavone) are supposed to be health-promoting dietary factors of plant origin. They are particularly abundant in seeds and other parts of many plant species belonging to Leguminosae. The most popular source of isoflavonoids in human diet is soy. Here, evidence is presented that isoflavonoids are regularly found in beer. Diethyl ether extracts of beer were fractionated on thin-layer chromatography-silica, (straight phase) and rechromatographed using a reversed phase high-performance liquid chromatography octadecylsilica column. The fractions were analyzed by two recently developed radioimmunoassays, the first of them being specific for diadzein/formononetin and the second one specific for genistein/biochanin A. The immunoreactivity was found only in fractions with the mobility corresponding to the positions of standards on control chromatograms. Additionally, 26 samples of bottled beer were analyzed for isoflavonoid content using the combination of reversed phase high-performance liquid chromatography and radioimmunoassay. The sum of the four isoflavonoids ranged from 1.26 to 29 nmol/L in individual beers. Formononetin was the major isoflavonoid (0.19-14.99 nmol/L), whereas the concentration of daidzein was several times lower (0.08-2.5 nmol/L). Genistein and biochanin A concentrations were comparable, ranging from 0.169-6.74 nmol/L and from 0.820-4.84 nmol/L for genistein and biochanin A, respectively. It is concluded that beer contains significant amounts of biologically active isoflavonoid phytoestrogens.

2,6-Bis((3,4-dihydroxyphenyl)-methylene)cyclohexanone (BDHPC)-induced apoptosis and p53-independent growth inhibition: synergism with genistein

Estrogen binds to two classes of proteins in the cells, the high-affinity estrogen receptor (ER) as well as a low affinity estrogen type II binding site (EBS-II). Methyl p-hydroxyphenyllactate (MeHPLA) is an endogenous ligand for EBS-II. Binding of MeHPLA to EBS-II has a growth regulatory effect in estrogen-responsive cells, and levels of MeHPLA are decreased in breast cancer due to degradation by a specific esterase. 2,6-bis((3, 4-dihydroxyphenyl)-methylene) cyclohexanone (BDHPC) is an esterase-resistant analogue of MeHPLA which binds irreversibly to EBS-II and inhibits growth of breast cancer cells. In the present study, we analyzed the mechanism of growth inhibition by BDHPC. Treatment with BDHPC resulted in accumulation of cells in G1 phase and apoptosis. The G1 accumulation was not dependent on a functional p53 gene. The G1-specific growth inhibition by BDHPC was found to act synergistically with the G2/M-specific inhibition induced by the tyrosine kinase inhibitor genistein, suggesting this drug combination could be effectively used in cancer treatment.

Flavonoids, dietary-derived inhibitors of cell proliferation and in vitro angiogenesis

Consumption of a plant-based diet can prevent the development and progression of chronic diseases associated with extensive neovascularization, including solid malignant tumors. In previous studies, we have shown that the plant-derived isoflavonoid genistein is a potent inhibitor of cell proliferation and in vitro angiogenesis. In the present study, we report that certain structurally related flavonoids are more potent inhibitors than genistein. Indeed, 3-hydroxyflavone, 3',4'-dihydroxyflavone, 2',3'-dihydroxyflavone, fisetin, apigenin, and luteolin inhibited the proliferation of normal and tumor cells, as well as in vitro angiogenesis, at half-maximal concentrations in the low micromolar range. We have previously demonstrated that genistein concentrations in the urine of subjects consuming a plant-based diet is 30-fold higher than in subjects consuming a traditional Western diet. The wider distribution and the more abundant presence of flavonoids in the plant kingdom, together with the present results, suggest that flavonoids may contribute to the preventive effect of a plant-based diet on chronic diseases, including solid tumors.

A novel radioimmunoassay for daidzein

A radioimmunoassay for daidzein was established, based on polyclonal antibodies against daidzein-4'-O-(carboxymethyl)ether-BSA. The sensitivity of the assay was 0.4 pg/tube; the intra- and interassay coefficients of variation varied from 4.1 to 11.5% and from 5.6 to 21.7%, respectively, depending upon the method (direct or extraction) and concentration of daidzein in the sample. The cross reactivities with other chemically related compounds, with the exception of 4'-derivatives of daidzein, were 2.4% for dihydrodaidzein, 1.3% for genistein, 1.5% for biochanin A, and 1.6% for equol, respectively. The method was used for measurement of daidzein levels in 105 normal human subjects and in three volunteers after consumption of a meal prepared from 125 g of cooked whole soybeans. The daidzein values obtained following diethyl ether extraction of human sera was only 8% of that obtained by direct radioimmunoassay. We suggest that this difference is caused by cross-reacting daidzein 4'-glucuronides and -sulfates present in serum. Using ether extraction, the basal serum levels of free daidzein were 0.11 ng/mL (0.43 nmol/L), with 14 subjects showing no detectable levels. Levels were detectable in all subjects with the direct assay with a mean value of 7.1 ng/mL (28.0 nmol/L). Peak levels were reached 4 hours after ingestion of the soybeans. The levels were 10.3 +/- 3.6 ng/mL (40.4 +/- 14.3 nmol/L) for free daidzein and 129.4 +/- 36.1 ng/mL (509 +/- 142 nmol/L) for total immunoreactive compounds. After 24 hours, the levels were still clearly distinguishable from the basal levels; the concentrations were 0.43 +/- 0.15 ng/mL (1.69 +/- 0.59 nmol/L) and 24.36 +/- 6.07 ng/mL (95.9 +/- 23.9) for free and total immunoreactive material, respectively. It is concluded that this is the first immunoassay for a phytoestrogen in human biological fluids, and for the first time serial assays of unconjugated daidzein in plasma have been possible.

A soy protein isolate rich in genistein and daidzein and its effects on plasma isoflavone concentrations, platelet aggregation, blood lipids and fatty acid composition of plasma phospholipid in normal men

The effects of consuming a soy protein isolate beverage powder (60 g/d for 28 d) vs. a casein supplement was evaluated in 20 male subjects who were randomly allocated into the two groups. A dramatic rise in plasma isoflavone concentrations was observed after supplementation in the soy protein group, the levels reaching 907 +/- 245 nmol/L for genistein (a 110-fold increase) and 498 +/- 102 nmol/L for daidzein (a 150-fold increase) as measured by isotope dilution gas chromatography - mass spectrometry. These concentrations are higher than previously reported for the plasma of Japanese subjects consuming a traditional diet (276 nmol/L and 107 nmol/L, respectively). No significant differences in collagen- or 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F2alpha (U46619)-induced platelet aggregation were observed in platelet-rich plasma from the two groups; the increase in plasma isoflavonoids from soy protein supplementation is not sufficient to significantly inhibit platelet aggregation ex vivo. Similarly, plasma total and HDL-cholesterol were not affected by protein supplementation, possibly because the men were normocholesterolemic at entry. Analysis of plasma phospholipid polyunsaturated fatty acid composition showed no differences between soy protein and casein supplementation. Previous investigations reported a significant alteration in fatty acid status in animals fed soy protein relative to those fed casein. The present studies indicate that although soy protein supplementation to a typical Western diet can increase plasma concentrations of isoflavones, this may not necessarily be sufficient to counter heart disease risk factors such as high plasma cholesterol and platelet aggregation.

Isotope dilution gas chromatographic-mass spectrometric method for the determination of isoflavonoids, coumestrol, and lignans in food samples

We present a method for the quantitative determination of the phytoestrogens formononetin, biochanin A, daidzein, genistein, and coumestrol and simultaneously the lignans secoisolariciresinol (SECO) and matairesinol in plant-derived foods. These compounds are measured by isotope dilution gas chromatography-mass spectrometry in the selected ion monitoring mode (ID/GC/MS/SIM) using synthesized deuterated internal standards for the correction of losses during the procedure. A three-step hydrolysis--a rehydration with distilled H2O, followed by enzymatic and acid hydrolysis--has been applied in order to convert the diphenolic glycosides into their respective aglycones. Purification and separation are carried out in two ion-exchange chromatographic steps followed by derivatization and GC-MS. The within-assay imprecision values vary 3.1-9.6% and the between-assay imprecision 7.0-21.2%. The mean recovery of authentic standards processed through the whole procedure varied from 95.5 to 105.5%. Values for some different food samples are presented. The simultaneous determination of the biologically most interesting phytoestrogens and lignans in foods has not been carried out previously and the method will be useful for screening of important foods in populations with different risk of cancer and coronary heart disease, and for metabolic studies.

Effect of diet on lignans and isoflavonoid phytoestrogens in chimpanzees

Diphenolic compounds belonging to the classes of lignans and isoflavonoids have been identified in urine of man and animals, including the chimpanzee. Some of these compounds, formed by intestinal bacteria from plant lignans and phytoestrogens, have been shown in animal studies to exhibit biological activities that suggest they could function as cancer-protective compounds. The effect of diet on urinary excretion of these compounds in the adult male chimpanzee has been studied. It was found that the chimpanzees consuming their regular food excreted large amounts of the isoflavonoid phytoestrogens, equol (mean +/- SE) (127.5 +/- 34.0 nmol/mg cr.) and daidzein (20.7 +/- 9.0 nmol/mg cr.) and the lignan, enterolactone (14.1 + 3.5 nmol/mg cr.). Small amounts of the lignan, enterodiol, (0.4 +/- 0.2 nmol/mg cr.) were also excreted. On all other four test diets (high protein, high carbohydrate, high vegetable, and high fat), the excretion was less, particularly on a high fat diet where the excretion of all diphenolic compounds was reduced by more than 90% to a level observed in omnivorous human subjects or women with breast cancer. These results suggest that diet profoundly influences the excretion of both animal lignans and phytoestrogens in urine. Because non-human primates are particularly resistant to mammary and genital carcinoma on estrogen treatment, the present data suggest that the very high levels of phytoestrogens and lignans as found during exposure to the regular diet may partially account for why these primates are so resistant to hormonal manipulations to induce cancer.

Isotope dilution gas chromatographic-mass spectrometric method for the determination of unconjugated lignans and isoflavonoids in human feces, with preliminary results in omnivorous and vegetarian women

We describe an isotope dilution gas chromatographic-mass spectrometric (GC/MS) method for the identification and quantitative determination of the lignans enterolactone, enterodiol, and matairesinol and the isoflavonoids daidzein, equol, O-desmethylangolensin, and genistein in feces. Following the addition of deuterated internal standards for all compounds, the feces samples are extracted and purified in several ion exchange chromatographic steps. Following formation of trimethylsilyl ethers, the samples are analyzed by combined capillary column GC/MS in the selective ion monitoring mode and corrected for all losses during the procedure using the deuterated internal standards. Results on the reliability of the method and values for nine Finnish omnivorous and nine vegetarian women are presented.

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.

Phytoestrogen content and estrogenic effect of legume fodder

This study is a summary of Finnish investigations of the phytoestrogen content of legume plants, red clover, white clover, alfalfa, and goat's rue. In addition to the chemical analyses, biological studies were performed. Uterine weight of immature rats was used as an indicator of the estrogenic effect of the fodder used. All red clover varieties studied contained estrogenic isoflavones, especially formononetin and biochanin-A. The phytoestrogen content varied from 1.0% to 2.5% of dry matter. The biological study of white clover showed a clear estrogenic effect not visible through chemical analysis. Alfalfa contains small quantities of formononetin and biochanin-A, but 25-65 ppm coumestrol in dry matter. The estrogenic effect of alfalfa was obvious in the biological study. Goat's rue did not contain any known phytoestrogens, and the biological study was completely negative.

Synthesis and labeling of isoflavone phytoestrogens, including daidzein and genistein

The synthesis of the important diphenolic isoflavone type phytoestrogens starting from the corresponding unprotected phenols and arylacetic acids is discussed. The aryl rings may carry additional alkyl, methoxy, and/or halogeno groups. Intermediate polyhydroxy deoxybenzoins can also be isolated in good yield. Isotopically labeled isoflavone phytoestrogens were prepared for use as internal standards in ion exchange chromatography and GC-MS selected ion monitoring (SIM technique). Traditional methods rely on total synthesis using deuterated starting materials for the preparation of labeled isoflavonoid structures. We have used successfully an application where the H/D exchange is performed within the finished molecular framework, based on the exchange of aromatic protons that are ortho or para to a phenolic OH group. By this method the deuterated products are available in an isotopic purity of 90% or higher.

Inhibition of human aromatase by mammalian lignans and isoflavonoid phytoestrogens

Isoflavonoid phytoestrogens and lignans in plants are known to be constituents of animal and human food and recently they have been found in human urine and other biological materials. These compounds have received increasing attention because of their interesting biological properties and possible role in human cancer and other diseases. The present study demonstrates that the main mammalian lignan enterolactone (trans-2,3-bis[(3-hydroxyphenyl)methyl]-butyrolactone) and some other diphenols are moderate or weak inhibitors of human estrogen synthetase (aromatase) and that this lignan binds to or near the substrate region of the active site of the P-450 enzyme. The inhibition is competitive with respect to testosterone and androstenedione, and the lignan affinity is 1/75-1/300 that of these natural substrates. It is suggested that the high concentration of lignans in vegetarians, by inhibiting aromatase in peripheral and/or cancer cells and lowering estrogen levels, may play a protective role as antipromotional compounds during growth of estrogen-dependent cancers.

Quantitative determination of lignans and isoflavonoids in plasma of omnivorous and vegetarian women by isotope dilution gas chromatography-mass spectrometry

The first quantitative method for the determination of both lignans and isoflavonoid phytoestrogens in plasma is presented. Using ion-exchange chromatography the diphenols are separated into two fractions 1) the biologically "active" fraction containing the free compounds + mono- and disulfates and 2) the biologically "inactive" fraction containing the mono- and diglucuronides and the sulfoglucuronides. After hydrolysis the fractions are further purified by solid phase extraction and ion exchange chromatography. Losses during the complete procedure are corrected for using radioactive estrogen conjugates during the first steps and later by adding deuterated internal standards of all compounds measured (matairesinol, enterodiol, enterolactone, daidzein, O-desmethylangolensin, equol, and genistein). The final determination is carried out by isotope dilution gas chromatography-mass spectrometry in the selected ion monitoring mode (GC/MS/SIM). The diphenols may be measured at concentrations as low as 0.2 to 1.0 nmol/l. Results of plasma analyses of all compounds in 27 pre- and postmenopausal omnivorous and vegetarian women are presented for the first time. The most important findings are that the free+sulfate fraction is low for genistein (3.8% of total), but as much as 21-25% of enterolactone and enterodiol occurs in this fraction. A good correlation between plasma and urine values was found. Total concentrations of individual compounds vary greatly between the subjects (from pmol/l to mumol/l), the vegetarians having higher values, particularly one vegan subject. The highest total enterolactone concentration value exceeded 1 mumol/l. It is concluded that a highly specific method for the assay of 3 lignans and 4 isoflavonoids in plasma has been developed. This method will be useful in future studies of lignan and isoflavonoid metabolism.

Identification in human urine of a natural growth inhibitor for cells derived from solid paediatric tumours

Partially purified urine of healthy human subjects contains several fractions able to inhibit the proliferation of cultured human neuroblastoma cells. One of the most active fractions was further analysed by gas chromatography-mass spectrometry and shown to contain genistein, a substance formed in the human body from precursors obtained by diet. Synthetic genistein was able to inhibit the proliferation of human neuroblastoma cells with a half-maximal effect at 5-10 mumol l-1 concentrations. Genistein displayed similar potencies in inhibiting the proliferation of cells derived from various other solid pediatric tumours. Our results suggest that genistein is a natural antineoplastic agent present in diet and that it could be useful for the therapy of paediatric tumours.

Dietary phytoestrogens and cancer: in vitro and in vivo studies

Thirty postmenopausal women (11 omnivores, 10 vegetarians and 9 apparently healthy women with surgically removed breast cancer) were investigated with regard to the association of their urinary excretion of estrogens, lignans and isoflavonoids (all diphenols) with plasma sex hormone binding globulin (SHBG). A statistically significant positive correlation between urinary total diphenol excretion and plasma SHBG was found which remained statistically significant after elimination of the confounding effect of body mass determined by body mass index (BMI). Furthermore we found a statistically significant negative correlation between plasma SHBG and urinary excretion of 16 alpha-hydroxyestrone and estriol which also remained significant after eliminating the effect of BMI. Furthermore we observed that enterolactone (Enl) stimulates the synthesis of SHBG by HepG2 liver cancer cells in culture acting synergistically with estradiol and at physiological concentrations. Enl was rapidly conjugated by the liver cells, mainly to its monosulfate. Several lignans and the isoflavonoids daidzein and equol were found to compete with estradiol for binding to the rat uterine type II estrogen binding site (the s.c. bioflavonoid receptor). It is suggested that lignans and isoflavonoids may affect uptake and metabolism of sex hormones by participating in the regulation of plasma SHBG levels and in this way influence their biological activity and that they may inhibit cancer cell growth like some flavonoids by competing with estradiol for the type II estrogen binding sites.

Phytoestrogens: new ligands for rat and human alpha-fetoprotein

The binding of the lignans, enterolactone, enterodiol, nordihydroguaiaretic acid (NDGA), and the isoflavonic phytoestrogen equol, to human and rat alpha-fetoprotein (AFP) was studied. They had differential inhibitory effects (NDGA greater than equol greater than enterolactone greater than enterodiol) on the binding of estrone and estradiol to rat AFP and the binding of unsaturated fatty acid to both rat and human AFP. Inhibition was dose-dependent. The apparent dissociation constants (Kd) for phytoestrogens binding to AFP were: Kd NDGA = 5 +/- 1.2.10(-7) M, Kd equol = 6.7 +/- 0.8.10(-6) M, Kd enterolactone = 1.7 +/- 0.4.10(-5) M and Kd enterodiol = 2.2 +/- 0.6.10(-5) M. The Kd for estrone binding to rat AFP was increased by increasing concentrations of equol, but the number of esterone binding sites remained unchanged. This, plus the results of double-reciprocal plots, suggests that they compete for the same site(s). NDGA also competitively inhibited estrone binding at low NDGA concentrations (increased Kd), but high concentrations induced conformational changes in rat AFP, as both Kd and the number of binding sites (n) were altered. Both rat and human AFPs underwent changes in electrophoretic behaviour and loss of immunoreactivity with increasing NDGA, suggesting that NDGA binding induces conformational changes in the AFPs. However, equol did not alter the electrophoretic or immunological properties of either rat or human AFP, providing further evidence for qualitative differences in the effects of these diphenols. These findings indicate that phytoestrogens could play a role in AFP-dependent normal and pathological growth and development.

Isotope dilution gas chromatographic-mass spectrometric method for the determination of lignans and isoflavonoids in human urine, including identification of genistein

We describe an isotope dilution gas chromatographic-mass spectrometric method for the quantitative determination of the lignans enterolactone, enterodiol and matairesinol and the isoflavonoids daidzein, equol, O-desmethylangolensin and genistein in urine. Furthermore we present the gas chromatographic/mass spectrometer identification of genistein. Urine samples were extracted on Sep-Pak cartridges, conjugated fractions were isolated by chromatography on the acetate form of DEAE-Sephadex and deuterated internal standards of all seven compounds were added to the samples before hydrolysis. The hydrolysate was extracted on a Sep-Pak cartridge and following chromatography on the acetate form of QAE-Sephadex two fractions were obtained: Fraction 1 contained equol, enterolactone, enterodiol, matairesinol and all estrogens and fraction 2 contained O-desmethylangolensin, daidzein and genistein. The latter was ready for gas chromatography/mass spectrometry, but the first one was further purified to eliminate the estrogens by chromatography on the carbonate form of QAE-Sephadex. Following silylation, the samples were analyzed by combined capillary column gas chromatography/mass spectrometry in the selective ion monitoring mode. The within-assay imprecision varied from 0.8-15.2% (mean 8.7%) and the between-assay imprecision from 4.1-13.9% (mean 9.3%), depending on compound and concentration level. The mean recovery of authentic standards added to urine extracts before hydrolysis varied from 96.6 to 105.5%. Values obtained from 10 Finnish omnivorous men are presented. Individual values for matairesinol (excretion range 3.3-59.9 nmol/24 h) and genistein (range 21.8-1180 nmol/24 h) in human urine have never been published before.