Soy isoflavonoids and cancer -- metabolism at the target site

Biosynthesis and Pharmacological Activities of Flavonoids, Triterpene Saponins and Polysaccharides Derived from Astragalus membranaceus

Astragalus membranaceus (A. membranaceus), a well-known traditional herbal medicine, has been widely used in ailments for more than 2000 years. The main bioactive compounds including flavonoids, triterpene saponins and polysaccharides obtained from A. membranaceus have shown a wide range of biological activities and pharmacological effects. These bioactive compounds have a significant role in protecting the liver, immunomodulation, anticancer, antidiabetic, antiviral, antiinflammatory, antioxidant and anti-cardiovascular activities. The flavonoids are initially synthesized through the phenylpropanoid pathway, followed by catalysis with corresponding enzymes, while the triterpenoid saponins, especially astragalosides, are synthesized through the universal upstream pathways of mevalonate (MVA) and methylerythritol phosphate (MEP), and the downstream pathway of triterpenoid skeleton formation and modification. Moreover, the Astragalus polysaccharide (APS) possesses multiple pharmacological activities. In this review, we comprehensively discussed the biosynthesis pathway of flavonoids and triterpenoid saponins, and the structural features of polysaccharides in A. membranaceus. We further systematically summarized the pharmacological effects of bioactive ingredients in A. membranaceus, which laid the foundation for the development of clinical candidate agents. Finally, we proposed potential strategies of heterologous biosynthesis to improve the industrialized production and sustainable supply of natural products with pharmacological activities from A. membranaceus, thereby providing an important guide for their future development trend.

Evaluation of the mutagenicity and antimutagenicity of soy phytoestrogens using micronucleus and comet assays of the peripheral blood of mice

Studies show that soy imparts many favorable properties in the human body, including the prevention of chronic diseases such as osteoporosis, heart disease, cancer, and diabetes. Soy is rich in isoflavones, and it is a candidate for the chemoprevention of diseases owing to its low toxicity. In this study, a soy phytoestrogen (with high levels of the isoflavones genistin and daidzein) was tested in mice to investigate its mutagenicity and genotoxicity using micronucleus and comet assays of mouse peripheral blood. Phytoestrogen (0.083, 0.83 and 8.3 mg/kg body weight) was evaluated with and without the chemotherapeutic agent cyclophosphamide. For the micronucleus assay, blood was collected before treatment and after 24 and 48 h. For the comet assay, blood was collected only after 24 h. Phytoestrogen was not mutagenic and reduced cyclophosphamide-induced DNA damage. The results from the comet assay revealed a reduction of DNA damage; however, phytoestrogen did induce genotoxic damage during the 24-h treatment. This genotoxic damage could have been repaired and was therefore not identified in the micronucleus assay, which detects mutations. The results suggested that the reduction of DNA damage observed in associated treatments could also reduce the side effects of chemotherapy. Moreover, they suggested that phytoestrogen might be a candidate of interest for the chemoprevention of cancer because it protects against DNA damage.

Effects of ortho-dihydroxyisoflavone derivatives from Korean fermented soybean paste on melanogenesis in B16 melanoma cells and human skin equivalents

In this study we investigated the inhibitory effects and possible mechanisms of action of 8'-hydroxydaidzein and 3'-hydroxydaidzein, two ortho-dihydroxyisoflavone derivatives from Korean fermented soybean paste, on melanogenesis in B16 murine melanoma cells. The two hydroxydaidzeins reduced melanin synthesis comparably to treatment with kojic acid, a proven whitening agent, in B16 melanoma cells. Furthermore, when in vitro human skin equivalents were treated with the hydroxydaidzeins, the levels of melanogenesis were significantly reduced relative to a kojic acid control. The RT-PCR results demonstrated that depigmentation was due to transcriptional repression of several melanogenesis genes, including microphthalmia-associated transcription factor (MITF), by the hydroxydaidzeins. The immunoblotting results confirmed that diminution of MITF expression subsequently decreased expression of tyrosinase, and tyrosinase-related proteins 1 and 2. Cumulatively, these results suggest that hydroxydaidzeins would be potent attenuators of melanin synthesis as well as effective inhibitors of hyperpigmentation in human skin.

Effect of genistein on the activities of cytochrome P450 3A and P-glycoprotein in Chinese healthy participants

To determine the effect of genistein on cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp) function using the probe substrates midazolam and talinolol, respectively. Eighteen healthy adult male participants were enrolled in a two-phase randomized crossover design. In each phase, the participants received placebo or genistein for 14 days. On the 15th day, midazolam and talinolol were administered and blood samples were obtained. Midazolam and talinolol pharmacokinetic parameter values were calculated and compared before and after genistein administration. Co-administration of genistein decreased the area under the concentration-time curve from 0 to 36 h (AUC 0-36) (143.65 ± 55.40 ng h/mL versus 126.10 ± 40.14 ng h/mL, p < 0.05), and the area under the concentration-time curve from zero to infinity (AUC 0-∞) (209.18 ± 56.61 ng h/mL versus 180.59 ± 43.03 ng h/mL, p < 0.05), and also maximum concentration (Cmax) of midazolam (48.86 ± 20.21 ng/mL versus 36.25 ± 14.35 ng/mL p < 0.05). Similarly, AUC 0-36 (2490.282 ± 668.79 ng h/mL versus 2114.46 ± 861.11 ng h/mL, p < 0.05), AUC 0-∞ (2980.45 ± 921.09 ng h/mL versus 2626.92 ± 1003.78 ng h/mL, p < 0.05) and Cmax of talinolol (326.58 ± 197.67 ng/mL versus 293.42 ± 127.19 ng/mL, p < 0.05) were reduced by genistein co-administration. The oral clearance of midazolam (1.68 ± 0.85 h-1 versus 3.98 ± 0.59 h-1, p < 0.05) and talinolol (3.34 ± 1.24 h-1 versus 3.79 ± 1.55 h-1, p<0.05) were increased by genistien significantly. Administration of genistein can result in a modest induction of CYP3A and possibly P-gp activity in healthy volunteers.

Antitumor and antiangiogenic activity of soy phytoestrogen on 7,12-dimethylbenz[alpha]anthracene-induced mammary tumors following ovariectomy in Sprague-Dawley rats

Soy phytoestrogen is often used as hormone replacement therapy to alleviate the symptoms of menopause in postmenopausal women. Since estrogen has been considered as an important risk factor for the development of breast carcinoma, we need to know whether it is safe for these postmenopausal women with breast cancer to take soy foods that are rich in phytoestrogen. In the present study, we investigated the efficacy of soy phytoestrogen on tumor proliferation, apoptosis, and angiogenesis in mammary tumors that had already formed in ovariectomized rats. We found that soy phytochemical extraction inhibited proliferation and induced apoptosis in vitro and in vivo, and it demonstrated better antitumor effects than single phytoestrogen. Soy phytochemical extraction also produced surprisingly good antiangiogenic effects, which were evidenced by lower microvascular density, reduced plasma vascular endothelial growth factor, and increased plasma endostatin levels. Our findings suggest that soy phytochemical extraction exerts significant antitumor and antiangiogenic activity in a postmenopausal animal model with breast cancer.

Major isoflavonoid contents of the 1-year-cultivated phytoestrogen-rich herb, Pueraria mirifica

Pueraria mirifica is a tuberous plant enriched with active phytoestrogens. There is no established information about the factors influencing isoflavonoid storage in the tubers. We investigated the tuberous storage of the major isoflavonoids of 1-year-old plants. Four cultivars of P. mirifica were cultivated in the same field trial during the same period to establish a unique plant age and differentiation under the same environment and soil conditions. The tubers collected from the 1-year-old plants in the summer, rainy season and winter were submitted to an HPLC analysis with a gradient system comprising 0.1% acetic acid and acetonitrile. Five major isoflavonoids, puerarin, daidzin, genistin, daidzein and genistein, were adopted as standards. P. mirifica tubers of different cultivars collected in the same season exhibited significant differences in individual and total isoflavonoid contents, showing chemovariety. P. mirifica tubers of the same cultivar collected from different seasons also exhibited significant differences in individual and total isoflavonoid contents, showing the influence of season. In conclusion, the tuberous storage of major isoflavonoids in 1-year-cultivated plants was greatly diverse and was strongly influenced by the season and plant genetics.

Bioavailability of soy isoflavones in rats Part I: application of accurate methodology for studying the effects of gender and source of isoflavones

There are limited and controversial reports about the effects of gender and source of isoflavones on their bioavailability. Moreover, several previous studies have not used appropriate methodology to determine the bioavailability of soy isoflavones, which requires comparing the area under the plasma concentration-time curve after both oral and intravenous injection (IV) administration. Therefore, the present study was conducted to determine the bioavailability of isoflavones from different sources following both oral and IV administration in male and female rats. Three sources of isoflavones; Novasoy (a commercial supplement), a mixture of synthetic aglycones (daidzein, genistein and glycitein) and a mixture of synthetic glucosides (daidzin, genistin and glycitin) were tested. Following administration, blood samples were collected at several time points (0, 10, 30 min and 1, 2, 8, 24, 48 h post oral gavage and 0, 10, 30, 45 min and 1, 2, 3, 4, 8 h post-IV dosing) and plasma isoflavones were measured by LC/MS. Bioavailability values for daidzein, genistein and glycitein were significantly (p <0.05) higher (up to sevenfold) in Novasoy and the glucoside forms of isoflavones compared with those of the aglycone forms. Moreover, significant (p <0.05) gender differences in the bioavailability of 7-hydroxyl-3-(4'-hydroxyphenyl)-chroman (a metabolite of daidzein), glycitein and daidzein were observed for Novasoy, with higher values in male rats. In summary, the source of isoflavones and the sex of rats had significant effects on isoflavone bioavailability.

UV–vis and FTIR–ATR spectroscopic techniques to study the inclusion complexes of genistein with β-cyclodextrins

The effect of beta-cyclodextrin (beta-CyD), (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CyD) and methyl-beta-cyclodextrin (Me-beta-CyD) complexation on the UV absorption of genistein (Gen) was studied in pure water. A phase solubility study was performed, according to the method reported by Higuchi and Connors, to evaluate the changes of isoflavone in the complexation state and the obtained diagrams suggested that it forms complexes with a stoichiometry of 1:1. Then, the solid complexes of genistein with these macrocycles in 1:1 molar ratio were prepared by the co-precipitation method and characterized by FTIR absorption spectroscopy in ATR geometry. The host-guest interactions have been evidenced by monitoring, in the FTIR-ATR spectra, the changes in some guest molecule bands relative to those observed in the spectra of the 1:1 physical mixtures and complexes. In particular, for the high-frequency O-H stretching band, a quantitative vibrational assignment of the observed sub-bands has been made. From the results, the inclusion phenomena have been discussed.

The biochemical alterations following administration of Kalpaamruthaa and Semecarpus anacardium in mammary carcinoma

BACKGROUND

Breast cancer is one of the most common cancers in women of developed and developing countries. Lipids, lipoproteins and lipid-metabolizing enzymes have been associated with the risk of breast cancer. Kalpaamruthaa (KA) is a modified Siddha preparation, which contains Semecarpus anacardium Linn. (SA), Emblica officinalis (EO) and honey.

OBJECTIVE

The present study was embarked to study the variations in lipids, lipid-metabolizing enzymes and lipoproteins in cancerous animals and the effect of KA on the lipid metabolism.

MATERIALS AND METHODS

Breast cancer was induced in rats by administrating 7,12-dimethylbenz(a)anthracene orally (25 mg/kg body weight). After 90 days of induction, KA (300 mg/kg body weight) and SA (200 mg/kg body weight) were administered for 14 days, by gastric intubations. The levels of lipids and lipid-metabolizing enzymes were analysed in control and experimental animals.

RESULTS AND CONCLUSION

The increased levels of total cholesterol, free cholesterol, phospholipids, triglycerides and free fatty acids and decreased levels of ester cholesterol in plasma, liver and kidney found in cancer suffering animals were reverted back to near normal levels on treatment with KA and SA. In mammary carcinoma bearing animals, the activities of total lipase, cholesterol ester synthase, and cholesterol ester hydrolase were significantly (p < 0.05) increased whereas lipoprotein lipase and lecithin cholesterol-acyl transferase were decreased. The levels of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) were increased and the level of high-density lipoprotein (HDL) was decreased. These alterations were recouped back upon treatment with KA as well as SA when compared to cancer animals. The effects of KA were found to be more effective than SA. No significant alterations were observed in herbal preparation control animals when compared to control animals.

Dietary Genistein Reduces Metastasis in a Postsurgical Orthotopic Breast Cancer Model

Metastatic spread, not primary tumor burden, is the leading cause of breast cancer deaths. For patient prognosis to improve, new systemic adjuvant therapies that are capable of effectively inhibiting the outgrowth of seeded tumor cells after surgical treatment of the primary breast tumor are needed. To facilitate the preclinical development of such therapies, relevant animal models of breast cancer metastasis that can mimic the postsurgical adjuvant setting are required. Here we developed a preclinical xenograft model of breast cancer metastasis where the primary tumor was removed by surgical resection before systemic adjuvant treatment. We used this model to assess the antimetastatic effect of postsurgical dietary intervention with the soy isoflavone genistein. The anticancer activity of genistein has been established in vitro and in vivo, however, few studies have tested the potential of genistein as an antimetastatic therapy. Using our model, we tested the efficacy of adjuvant treatment with genistein to inhibit the outgrowth of metastases postsurgery. To establish primary tumors, human breast carcinoma cells, MDA-MB-435/HAL, were implanted into the mammary fat pad of female nude mice. Primary tumors were left to grow for 5 weeks before being surgically removed. Mice were then randomized into two diet groups: control soy-free diet versus genistein-supplemented diet. Five weeks later, metastatic burden was assessed. Genistein reduced the percent metastatic burden in the lungs by 10-fold. These results indicate that dietary intervention following cancer surgery can affect the outgrowth of seeded tumor cells. The availability of well-characterized, clinically relevant animal models for studying factors that regulate metastatic outgrowth postsurgery will provide an important tool for developing new systemic adjuvant therapies.

Mass spectrometric methods for the determination of flavonoids in biological samples

There is an ever-increasing interest in the biological effects of the bioflavonoids, members of the large group of plant polyphenols. Because of the aromatic character of these compounds, they have been analyzed by several chromatographic methods. In the case of high-performance liquid chromatography, they are readily detected by their ultraviolet absorbance or electrochemical properties. More evidence that the bioflavonoids undergo extensive metabolism during uptake from the gut and distribution around the body and in specific tissues is accumulating. In addition, free radical products at sites of inflammatory processes react with bioflavonoids and their metabolites, generating important new compounds of as yet unknown properties. For these reasons, careful examination of the chemical nature of bioflavonoids and their products in biological systems is absolutely required. Combination of mass spectrometry with the various chromatographic methods has proved to be highly successful in this regard. This review of the literature on the bioflavonoids is focused on the methods that are currently available for their qualitative and quantitative analysis by mass spectrometry and covers the period 2001-2003. Emphasis is placed on the description and value of existing methods, followed by an examination of emerging technologies.

Mechanisms of formation of chromosomal aberrations: insights from studies with DNA repair-deficient cells

In order to understand the mechanisms of formation of chromosomal aberrations, studies performed on human syndromes with genomic instability can be fruitful. In this report, the results from studies in our laboratory on the importance of the transcription-coupled repair (TCR) pathway on the induction of chromosomal damage and apoptosis by ultraviolet light (UV) are discussed. UV61 cells (hamster homologue of human Cockayne's syndrome group B) deficient in TCR showed a dramatic increase in the induction of chromosomal aberrations and apoptosis following UV treatment. At relatively low UV doses, the induction of chromosomal aberrations preceded the apoptotic process. Chromosomal aberrations probably lead to apoptosis and most of the cells had gone through an S phase after the UV treatment before entering apoptosis. At higher doses of UV, the cells could go into apoptosis already in the G1 phase of the cell cycle. Abolition of TCR by treatment with alpha-amanitin (an inhibitor of RNA polymerase II) in the parental cell line AA8 also resulted in the induction of elevated chromosomal damage and apoptotic response similar to the one observed in UV61 cells treated with UV alone. This suggests that the lack of TCR is responsible for the increased frequencies of chromosomal aberrations and apoptosis in UV61 cells. Hypersensitivity to the induction of chromosomal damage by inhibitors of antitopoisomerases I and II in Werner's syndrome cells is also discussed in relation to the compromised G2 phase processes involving the Werner protein.

Modulatory effect of soy isoflavones on biochemical alterations mediated by TPA in mouse skin model

Exposure to various carcinogenic agents along with other contributing factors increase the risk of cancer formation. The current study assesses the effect of soy isoflavones on the biochemical events associated with tumor promotion in mouse skin. 12-O-tetradecanoyl phorbol-13-acetate (TPA), a well-known tumor promoter on topical application depletes the reduced glutathione content (GSH) and down regulates the activities of its metabolizing enzyme, glutathione-S-transferase (GST) and the activities of antioxidant enzymes. However, the ornithine decarboxylase (ODC) activity and unscheduled DNA synthesis are elevated on single topical application of TPA to the dorsal cutaneous portions of the mice. Topical applications of soy isoflavones, half-an-hour prior to the application of TPA prevented the induction of ODC activity and DNA synthesis mediated by TPA (p < 0.01). The content of GSH, GST and antioxidant enzymes (p < 0.05) was also recovered significantly by soy isoflavones in a dose dependent manner. Parallel to these effects, pretreatment with the soy isoflavones also reduced hydrogen peroxide (H2O2) content (p < 0.05) at 1.0 and 2.0 microg/0.2 ml vehicle/animal. Therefore, we conclude that soy isoflavones are potentially protective against TPA induced biochemical alterations.

Soy isoflavone phyto-pharmaceuticals in interleukin-6 affections. Multi-purpose nutraceuticals at the crossroad of hormone replacement, anti-cancer and anti-inflammatory therapy

Interleukin-6 is a pleiotropic cytokine which plays a crucial role in immune physiology and is tightly controlled by hormonal feedback mechanisms. After menopause or andropause, loss of the normally inhibiting sex steroids (estrogen, testosterone) results in elevated IL6 levels that are further progressively increasing with age. Interestingly, excessive IL6 production promotes tumorigenesis (breast, prostate, lung, colon, ovarian), and accounts for several disease-associated pathologies and phenotypical changes of advanced age, such as osteoporosis, rheumatoid arthritis, multiple myeloma, neurodegenerative diseases and frailty. In this respect, pharmacological modulation of IL6 gene expression levels may have therapeutical benefit in preventing cancer progression, ageing discomforts and restoring immune homeostasis. Although "plant extracts" are used in folk medicine within living memory, it is only since the 20th century that numerous scientific investigations have been performed to discover potential health-protective food compounds or "nutraceuticals" which might prevent cancer and ageing diseases. About 2000 years ago, Hippocrates already highlighted "Let food be your medicine and medicine be your food". Various nutrients in the diet play a crucial role in maintaining an "optimal" immune response, such that deficient or excessive intakes can have negative consequences on the organism's immune status and susceptibility to a variety of pathologies. Over the last few decades, various immune-modulating nutrients have been identified, which interfere with IL6 gene expression. Currently, a broad range of phyto-pharmaceuticals with a claimed hormonal activity, called "phyto-estrogens", is recommended for prevention of various diseases related to a disturbed hormonal balance (i.e. menopausal ailments and/or prostate/breast cancer). In this respect, there is a renewed interest in soy isoflavones (genistein, daidzein, biochanin) as potential superior alternatives to the synthetic selective estrogen receptor modulators (SERMs), which are currently applied in hormone replacement therapy (HRT). As phyto-chemicals integrate hormonal ligand activities and interference with signaling cascades, therapeutic use may not be restricted to hormonal ailments only, but may have applications in cancer chemoprevention and/or NF-kappaB-related inflammatory disorders as well.

Distribution of breakpoints induced by etoposide and X-rays along the CHO X chromosome

SORB (selected observed residual breakpoints) induced by ionizing radiation or endonucleases are often non-randomly distributed in mammalian chromosomes. However, the role played by chromatin structure in the localization of chromosome SORB is not well understood. Anti-topoisomerase drugs such as etoposide are potent clastogens and unlike endonucleases or ionizing radiation, induce DNA double-strand breaks (DSB) by an indirect mechanism. Topoisomerase II (Topo II) is a main component of the nuclear matrix and the chromosome scaffold. Since etoposide leads to DSB by influencing the activity of Topo II, this compound may be a useful tool to study the influence of the chromatin organization on the distribution of induced SORB in mammalian chromosomes. In the present work, we compared the distribution of SORB induced during S-phase by etoposide or X-rays in the short euchromatic and long heterochromatic arms of the CHO9 X chromosome. The S-phase stage (early, mid or late) at which CHO9 cells were exposed to etoposide or X-rays was marked by incorporation of BrdU during treatments and later determined by immunolabeling of metaphase chromosomes with an anti-BrdU FITC-coupled antibody. The majority of treated cells were in late S-phase during treatment either with etoposide or X-rays. SORB induced by etoposide mapped preferentially to Xq but random localization was observed for SORB produced by X-rays. Possible explanations for the uneven distribution of etoposide-induced breakpoints along Xq are discussed.

Metabolism of the soy isoflavones daidzein, genistein and glycitein in human subjects. Identification of new metabolites having an intact isoflavonoid skeleton

Epidemiological studies have associated high soy intake with a lowered risk for certain hormone-dependent diseases. Soy and soy foods are rich sources of isoflavones, which have been shown to possess several biological activities. In this study, the metabolism of soy isoflavones daidzein, genistein and glycitein was investigated in human subjects. The aim was to find and identify urinary phase I metabolites of isoflavones, which have an intact isoflavonoid skeleton, and which might possess some bioactivity. Six volunteers included three soy bars per day into their normal western diet for a 2-week period. Daily urine samples were collected before, and after the supplementation period. Urine samples were hydrolyzed with Helix pomatia, extracted with diethyl ether, purified with Sephadex LH-20 chromatography, and analyzed as trimethylsilyl derivatives using gas chromatography-mass spectrometry (GC-MS). The structures of the isoflavone metabolites were identified using authentic reference compounds. The metabolites, for which authentic reference compounds were not available, were identified by the interpretation of mass spectra. Several new isoflavone metabolites were identified, and the presence of previously reported metabolites confirmed. The metabolic pathways of daidzein, genistein and glycitein are presented on the basis of the identification of the metabolites in human urine after soy supplementation.

Inhibition of the proteasome activity, a novel mechanism associated with the tumor cell apoptosis-inducing ability of genistein

Epidemiological studies have suggested that increased soy consumption is associated with reduced cancer occurrence. Genistein, a soy isoflavone, has been reported to inhibit the growth of human tumor cells although the involved molecular mechanisms are not clearly defined. Here we report that genistein inhibits the proteasomal chymotrypsin-like activity in vitro and in vivo. Computational docking studies suggest that the interaction of genistein with the proteasomal beta 5 subunit is responsible for inhibition of the chymotrypsin-like activity. Inhibition of the proteasome by genistein in prostate cancer LNCaP and breast cancer MCF-7 cells is associated with accumulation of ubiquitinated proteins and three known proteasome target proteins, the cyclin-dependent kinase inhibitor p27(Kip1), inhibitor of nuclear factor-kappa B (I kappa B-alpha), and the pro-apoptotic protein Bax. Genistein-mediated proteasome inhibition was accompanied by induction of apoptosis in these solid tumor cells. Finally, genistein induced proteasome inhibition and apoptosis selectively in simian virus 40-transformed human fibroblasts, but not in their parental normal counterpart. Our results suggest that the proteasome is a potential target of genistein in human tumor cells and that inhibition of the proteasome activity by genistein might contribute to its cancer-preventive properties.

Mass spectrometric methods for the analysis of chlorinated and nitrated isoflavonoids: a novel class of biological metabolites

Electrospray ionization combined with tandem mass spectrometry was applied to a study of some representative chlorinated and nitrated isoflavones-potential metabolites of isoflavones in inflammatory cells. Upon collision-induced dissociation of deprotonated [M - H](-) ions of these compounds, a number of structurally characteristic product ions were produced. The product ion analysis of 3'- and 8-chlorodaidzein in the tandom mass spectra led to ready differentiation of these isomers. 3-Nitro derivatives of both genistein and daidzein have product ions due to the losses of HNO(2) and two OH groups. Chlorinated derivatives of isoflavones were detected in cell-based experiments and their structures were proposed by comparing the tandem mass spectra of their product ions with those of standards. This work provides a suitable analytical basis to aid the characterization of chlorinated and nitrated metabolites in studies in vivo and in vitro.

Use of exfoliated cells from target tissues to predict responses to bioactive food components

A host of bioactive food components have been proposed to promote health and reduce the risk of disease states. It is clear that not all individuals respond identically to these essential and nonessential food components. Genetic polymorphisms may influence absorption, metabolism and accumulation of bioactive food components, thereby influencing their actions in target tissues. Unfortunately, serum concentrations of bioactive food components may not correlate with tissue concentrations and may therefore under- or overestimate the response in target tissues. Exfoliated cells may be useful to assess the actions of nutrients in specific tissues. Although not extensively examined, evidence already suggests the usefulness of these cells in predicting changes in gene expression, DNA methylation, DNA damage, protein expression and accumulation of dietary components. Although there are limitations on the collection of exfoliated cells, the inaccessibility of tissues they can represent raises intriguing possibilities for their ability to predict the outcome of nutritional intervention studies.

Phyto-oestrogens and osteoporosis: what is a safe dose?

Hormone replacement therapy (HRT) for preventing loss of bone following the menopause is utilised by only 8-10 % of possible users, largely due to a fear of increased risk of breast cancer. Plant oestrogen-like compounds (phyto-oestrogens) have been proposed as an alternative to HRT to prevent osteoporosis. One class of phyto-oestrogens (the isoflavones) is found in soya foods and red clover. The food industry is developing a wide variety of new foods containing soya to substantially increase isoflavone intake, as well as extracting isoflavones from soya and clover to use as additives to non-soya foods. Pharmaceutical companies are also preparing isoflavone extracts to be used in pill form. In each case the targeted delivery is approximately 50 mg of isoflavones/d. Is this dose of isoflavones safe? In this review of the current literature, it is concluded that isoflavones consumed orally and in doses below 2 mg/kg body weight per d should be considered safe for most population groups. Whether these doses are sufficient to prevent osteoporosis is a separate matter.

Measurement of intact sulfate and glucuronide phytoestrogen conjugates in human urine using isotope dilution liquid chromatography-tandem mass spectrometry with [13C(3)]isoflavone internal standards

A method has been developed for the analysis of phytoestrogens and their conjugates in human urine using liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Stable isotopically labeled [13C(3)]daidzein and [13C(3)]genistein were synthesized and used as internal standards for isotope dilution mass spectrometry. Free aglycons and intact glucuronide, sulfate, diglucuronide, disulfate, and mixed sulfoglucuronide conjugates of isoflavones and lignans were observed in naturally incurred urine samples. Sample pretreatment was not necessary, other than addition of internal standards and pH adjustment. Urine was injected directly onto the analytical column. The limits of detection were generally <50ng/ml, precision was generally <10% CV for conjugates. Total hydrolyzed daidzein and genistein were measured against quality assurance urine sample and were accurate to within 12%. The accuracy of conjugate measurement can not be ascertained, as no reference samples are available. The mean sum of daidzein and its conjugates was within 20% of the hydrolyzed value. Concentrations of the free aglycons of up to 22% of genistein and 18% of daidzein were observed. The average pattern was ca. 54% 7-glucuronide, 25% 4(')-glucuronide, 13% monosulfates, 7% free daidzein, 0.9% sulfoglucuronides, 0.4% diglucuronide, and <0.1% disulfate. Selective enzymatic deconjugation with glucuronidase and mixed glucuronidase/sulfatase were used to validate the accuracy of the quantitation of the intact daidzein conjugates. There were no apparent sex differences, or conditioning effects on the conjugation profile of isoflavones after chronic dosing.