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

Factors to consider in the association between soy isoflavone intake and breast cancer risk

It has been suggested that soy isoflavones have protective effects against breast cancer. However, data from epidemiological studies are not conclusive. A recent meta-analysis showed that soy intake was inversely associated with breast cancer risk in Asian but not Western populations, which indicates that protection against breast cancer may require that women consume levels of soy typical in Asian diets. In addition to the amount of soy isoflavones consumed, the form and food source of isoflavones, timing of isoflavone exposure, estrogen receptor status of tumors, and equol-producer status and hormonal profile of individuals may modify the association between soy isoflavone intake and the risk of breast cancer. These factors might explain the heterogeneity of results from studies. This present report contrasts background data from Japanese and Western women to identify the potential modifying of these factors.

Soy, phyto-oestrogens and male reproductive function: a review

There is growing interest in the possible health threat posed by the effects of endocrine disruptors on reproduction. Soy and soy-derived products contain isoflavones that mimic the actions of oestrogens and may exert adverse effects on male fertility. The purpose of this review was to examine the evidence regarding the potential detrimental effects of soy and phyto-oestrogens on male reproductive function and fertility in humans and animals. Overall, there are some indications that phyto-oestrogens, alone or in combination with other endocrine disruptors, may alter reproductive hormones, spermatogenesis, sperm capacitation and fertility. However, these results must be interpreted with care, as a result of the paucity of human studies and as numerous reports did not reveal any adverse effects on male reproductive physiology. Further investigation is needed before a firm conclusion can be drawn. In the meantime, caution would suggest that perinatal phyto-oestrogen exposure, such as that found in infants feeding on soy-based formula, should be avoided.

Sex-based cardiac physiology

Biological sex plays an important role in normal cardiac physiology as well as in the heart's response to cardiac disease. Women generally have better cardiac function and survival than do men in the face of cardiac disease; however, this sex difference is lost when comparing postmenopausal women with age-matched men. Animal models of cardiac disease mirror what is seen in humans. Sex steroid hormones contribute significantly to sex-based differences in cardiac disease outcomes. Estrogen is generally considered to be cardioprotective, whereas testosterone is thought to be detrimental to heart function. Environmental estrogen-like molecules, such as phytoestrogens, can also affect cardiac physiology in both a positive and a negative manner.

Clinical development of novel proteasome inhibitors for cancer treatment

BACKGROUND

Emerging evidence demonstrates that targeting the tumor proteasome is a promising strategy for cancer therapy.

OBJECTIVE

This review summarizes recent results from cancer clinical trials using specific proteasome inhibitors or some natural compounds that have proteasome-inhibitory effects.

METHODS

A literature search was carried out using PubMed. Results about the clinical application of specific proteasome inhibitors and natural products with proteasome-inhibitory activity for cancer prevention or therapy were reviewed.

RESULTS/CONCLUSION

Bortezomib, the reversible proteasome inhibitor that first entered clinical trials, has been studied extensively as a single agent and in combination with glucocorticoids, cytotoxic agents, immunomodulatory drugs and radiation as treatment for multiple myeloma and other hematological malignancies. The results in some cases have been impressive. There is less evidence of bortezomib's efficacy in solid tumors. Novel irreversible proteasome inhibitors, NPI-0052 and carfilzomib, have also been developed and clinical trials are underway. Natural products with proteasome-inhibitory effects, such as green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG), soy isoflavone genistein, and the spice turmeric compound curcumin, have been studied alone and in combination with traditional chemotherapy and radiotherapy against various cancers. There is also interest in developing these natural compounds as potential chemopreventive agents.

Effects of equol on oxidized low-density lipoprotein-induced apoptosis in endothelial cells

AIM

Equol is the main active product of daidzein metabolism, produced via specific microflora in the gut. This study aimed to clarify the effects of equol on oxidized low-density lipoprotein (OX-LDL)-stimulated apoptosis in human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were cultured in the presence of OX-LDL, and cell apoptosis was monitored by evaluating of DNA fragmentation and the production of cytoplasmic histone-associated DNA fragments. We simultaneously evaluated the level of cellular superoxide and nitric oxide (NO) and the effects of the anti-oxidant activity of equol on apoptosis.

RESULTS

We found that equol inhibited the induction of apoptosis in response to exposure of HUVECs to OX-LDL. Treatment of cells with equol led to a significant reduction in superoxide production by NAD(P)H oxidase and also to a significant increase in NO production. We further observed an effect of equol on the suppression of OX-LDL uptake.

CONCLUSIONS

These results suggested that equol might contribute to a reduced level of OX-LDL-stimulated apoptosis linked to the reduced generation of intracellular reactive oxygen species (ROS).

Prostatic soy isoflavone concentrations exceed serum levels after dietary supplementation

BACKGROUND

The effects of soy isoflavones on prostate cancer may be concentration-dependent. The impact of soy supplementation on isoflavone concentrations in prostate tissues and serum remain unclear.

OBJECTIVE

To assess and compare concentrations of soy isoflavones in prostate tissue and serum among 19 men with prostate cancer who had elected to undergo radical prostatectomy.

METHODS

Participants were randomized to receive either daily soy supplements (82 mg/day aglycone equivalents) or placebos for 2 weeks (14 days) prior to surgery. Serum samples were obtained at the time of the surgery. Isoflavone concentrations were measured by HPLC/ESI-MS-MS.

RESULTS

The median (25th, 75th percentile) total isoflavone concentration in the isoflavone-supplemented group was 2.3 micromol/L (1.2, 6.9) in the prostate tissue and 0.7 micromol/L (0.2, 1.2) in the serum. Total isoflavone concentrations in this group were an average of approximately 6-fold higher in prostate tissue compared to serum; the tissue versus serum ratio was significantly lower for genistein than daidzein, 4-fold versus 10-fold, P = 0.003. Tissue and serum levels of isoflavones among the placebo group were negligible with a few exceptions.

CONCLUSIONS

The findings from the present study suggest that prostate tissue may have the ability to concentrate dietary soy isoflavones to potentially anti-carcinogenic levels.

Effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged male rats

There are limited reports on the bioavailability and pharmacokinetics of isoflavones in elderly humans and aged animals. The present study was conducted to assess the effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged (20 month old) male Fischer-344 (F-344) rats. The F-344 rat, developed by the National Institute on Aging, is an inbred rat model that is commonly used for aging studies and resembles many features of aging humans. Three sources of isoflavones; Novasoy (a commercial supplement), a mixture of synthetic aglycons (daidzein, genistein and glycitein), and a mixture of synthetic glucosides (daidzin, genistin, and glycitin) were tested. Following administration, blood samples were collected at different times (0-48 h post-oral gavage and 0-8 h post-IV dosing). Plasma isoflavones and 7-hydroxy-3-(4'-hydroxyphenyl)-chroman (a metabolite of daidzein) were measured by LC/MS. The extent of absorption was determined by comparing the area under the curve (AUC) of the plasma-concentration time curve after intravenous (IV) administration with that following oral administration. The extent of bioavailability was then calculated as: %bioabailability = (AUC(or)/AUC(IV))x(Dose(IV)/Dose(or))x100. Bioavailabilities for genistein were significantly (p = 0.013) higher for the aglycon (35 +/- 9%) compared with the glucoside forms (11 +/- 3%). In contrast, the bioavailabilities for glycitein were significantly (p = 0.011) higher in Novasoy (27 +/- 13%) and the glucoside form (21 +/- 10%) compared with the aglycon (8 +/- 3%). No significant differences in the bioavailability of daidzein were observed in aged rats dosed with aglycon, glucoside or Novasoy. However, aged rats were able to produce equol as early as 8 h post-dosing. In summary, the source of isoflavones had significant effects on genistein and glycitein bioavailability in aged male rats.

MLL leukemia-associated rearrangements in peripheral blood lymphocytes from healthy individuals

Chromosomal translocations are characteristic of hematopoietic neoplasias and can lead to unregulated oncogene expression or the fusion of genes to yield novel functions. In recent years, different lymphoma/leukemia-associated rearrangements have been detected in healthy individuals. In this study, we used inverse PCR to screen peripheral lymphocytes from 100 healthy individuals for the presence of MLL (Mixed Lineage Leukemia) translocations. Forty-nine percent of the probands showed MLL rearrangements. Sequence analysis showed that these rearrangements were specific for MLL translocations that corresponded to t(4;11)(q21;q23) (66%) and t(9;11) (20%). However, RT-PCR failed to detect any expression of t(4;11)(q21;q23) in our population. We suggest that 11q23 rearrangements in peripheral lymphocytes from normal individuals may result from exposure to endogenous or exogenous DNA-damaging agents. In practical terms, the high susceptibility of the MLL gene to chemically-induced damage suggests that monitoring the aberrations associated with this gene in peripheral lymphocytes may be a sensitive assay for assessing genomic instability in individuals exposed to genotoxic stress.

Gastrointestinal absorption and metabolism of soy isoflavonoids in ileal-canulated swine

The relative contribution of the small intestine to absorption and microbial metabolism of ingested isoflavonoids (IFN) was investigated in swine with canulae in distal ilea to facilitate collection of chyme (canula open). Weaned swine were fed a single meal containing ground roasted soybean and corn with canulae open followed by a second test soy diet at 48 h with canulae closed to allow passage of chyme into the large intestine. All remaining feedings were soy-free (corn-casein diet). Ileal effluent and urine were collected for 16 and 48 h, respectively, and analyzed for IFN and microbial metabolites of IFN. IFN in ileal effluent were present entirely as aglycones. IFN equivalents excreted for 24 h after ingesting the soy diet were not significantly different when canulae were open or closed. Urinary IFN aglycone equivalents on day 2 were similar to those on day 1 when canulae remained closed, but less than 10% of that on day 1 when canulae were open for 16 h postfeeding. Urinary concentrations of dihydrodaidzein, dihydrogenistein, O-desmethylangolensin, and equol exceeded IFN aglycone equivalents. These findings suggest extensive preabsorptive conversion of IFN glucosides to aglycones in the small intestine and relatively efficient microbial metabolism of IFN in weaned swine.

Isoflavones in urine, saliva, and blood of infants: data from a pilot study on the estrogenic activity of soy formula

In the United States, about 25% of infant formula sold is based on soy protein, which is an important source of estrogenic isoflavones in the human food supply. Nevertheless, few studies report isoflavone levels in infants. We did a partly cross-sectional and partly longitudinal pilot study to examine children's exposure to isoflavones from different feeding methods. A total of 166 full-term infants between birth and 1 year of age were recruited into soy formula, cow milk formula, or breast milk regimens according to their feeding histories. A total of 381 urine, 361 saliva, and 88 blood samples were collected at 382 visits. We used automated online solid-phase extraction coupled to high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for measuring three isoflavones (daidzein, genistein, and equol) in urine, and used similar LC/MS/MS techniques for saliva and blood spots. Concentrations of daidzein and genistein were undetectable in most blood or saliva samples from children fed breast milk or cow milk formula. The proportion of non-detectable values was somewhat lower in urine than in the other matrices. Concentrations of equol were detectable only in a few urine samples. For both daidzein and genistein, urine contained the highest median concentrations, followed by blood and then saliva. Urinary concentrations of genistein and daidzein were about 500 times higher in the soy formula-fed infants than in the cow milk formula-fed infants. The correlations between matrices for either analyte were strikingly lower than the correlation between the two analytes in any single matrix. We did not find significant correlations between isoflavone concentrations and the levels of certain hormones in children fed soy formula. Our results, based on much larger numbers of infants, strongly confirm previous reports, but whether phytoestrogens in soy formula are biologically active in infants is still an open question. We plan further longitudinal studies focusing on physical and developmental findings reflecting the effects of estrogen exposure.

Synergy research: vitamins and secondary plant components in the maintenance of the redox-homeostasis and in cell signaling

The maintenance of the redox-homeostasis is an essential task of antioxidants. Reactive oxygen species (ROS) formed during oxidative stress can potentially damage the normal cellular functions and support pathological processes like atherosclerosis in vessels or malignant growth in other tissues, but also the aging process. However, recent findings link ROS also to cell survival and/or proliferation, which revolutionises the age-old dogmatic view of ROS being exclusively involved in cell damage and death. Low concentrations of hydrogenperoxide e.g. are involved in cell signaling and can activate mitogen-activated kinases (MAPK) to initiate cell growth. Nutritional antioxidants like vitamin C or E can promote endothelial cell growth, but can also inhibit growth of muscle cells, and influence MAPK. Thus, keeping the redox-homeostasis in a steady state especially in the context of tissue regeneration appears to be more important than previously known and seems to be a controlled synergistic action of antioxidants and ROS. The present review summarizes the properties and functions of ROS and nutritional antioxidants like the vitamins C and E, and polyphenols in redox-homeostasis. Their relevance in the treatment of various diseases is discussed in the context of a multitarget therapy with nutraceuticals and phytotherapeutic drugs.

Phytoestrogenic isoflavonoids in epidemiologic and clinical research

Isoflavones (IFLs) are natural products to which humans have been traditionally exposed predominantly through soy foods; more recently humans are also exposed to them through soy protein addition to processed foods or through supplements. They are structurally similar to steroidal estrogens and can exert estrogenic or antiestrogenic effects depending on their concentrations and on the tissue considered. These properties qualify IFLs to be classified as phytoestrogens and are believed to account for many of the biological effects observed for soy and/or IFL exposure including benefits for bone and heart health or prevention of menopausal symptoms and certain types of cancer. In order to evaluate the function of IFLs, alone or when exposure happens through soy intake, pharmacokinetics and bioavailability are critical issues to be considered in epidemiologic and clinical research. For this purpose precise, accurate, robust, fast, and affordable techniques for IFL analyses are required.

Influence of food polyphenols on aryl hydrocarbon receptor-signaling pathway estimated by in vitro bioassay

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxic and biological actions of many aromatic environmental pollutants such as dioxins. We investigated AhR activation by some vegetable constituents, including flavonoids, tannins, and related polyphenols, using an AhR-based in vitro bioassay for dioxins. Among the compounds tested, marked AhR activation was exhibited by isoflavones such as daidzein, resveratrol (a stilbene) structure, some flavanones such as naringenin, and flavones such as baicalein. On the other hand, some flavones such as apigenin, flavonols such as quercetin, and anthraquinones such as emodin, showed notable inhibitory effects on the in vitro activation of AhR induced by the dioxin [2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)]. In addition, AhR-mediated interactions between AhR and some plant extracts, including those from vegetables, fruits, herbs, and teas, were tested by using the AhR-based bioassay. Of the samples tested, some leafy green vegetables, citrus fruits, and herbs that contain food polyphenolics showed AhR-based interactions at high concentrations. On the basis of these finding, we discuss the implications of polyphenols on the AhR-signaling pathway.

Plasma isoflavones and subsequent risk of prostate cancer in a nested case-control study: the Japan Public Health Center

PURPOSE

The incidence of prostate cancer is much lower in Japanese than Western populations. Given the preventive effects of isoflavones on carcinogenesis in the prostate in many nonhuman studies and the high consumption of isoflavones in Japanese, this low incidence may be partly due to the effects of soy.

PATIENTS AND METHODS

We conducted a nested case-control study within the Japan Public Health Center-based Prospective Study. A total of 14,203 men aged 40 to 69 years who had returned the baseline questionnaire and provided blood samples were observed from 1990 to 2005. During a mean of 12.8 years of follow-up, 201 newly diagnosed prostate cancers were identified. Two matched controls for each case were selected from the cohort. Conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs for prostate cancer in relation to plasma levels of isoflavone.

RESULTS

Plasma genistein level tended to be inversely associated with the risk of total prostate cancer. Although plasma daidzein showed no association, the highest tertile for plasma equol, a metabolite of daidzein, was significantly associated with a decreased risk of total prostate cancer (OR = 0.60; 95% CI, 0.36 to 0.99; P(trend) = .04). These inverse associations were strengthened after analysis was confined to localized cases, with ORs in the highest group of plasma genistein and equol compared with the lowest of 0.54 (95% CI, 0.29 to 1.01; P(trend) = .03) and 0.43 (95% CI, 0.22 to 0.82; P(trend) = .02), respectively. Plasma isoflavone levels were not statistically significantly associated with the risk of advanced prostate cancer.

CONCLUSION

Isoflavones may prevent the development of prostate cancer.

Microbial metabolism of soy isoflavones by human intestinal bacterial strains

Intestinal bacteria play an important role for the metabolism of soy isoflavonoids. When soy foods are consumed, the soy isoflavone glucosides are metabolized into their aglycones and the related isoflavonoids by intestinal bacteria. We designed an in vitro microbial metabolic system using 29 commercially available human intestinal bacterial strains and elucidated the metabolism of soy isoflavone glucosides. The strains were classified into three categories, which were 14 facultative anaerobes, 13 obligate anaerobes, and 2 aerobes. Almost all facultative anaerobe strains metabolized soy isoflavone glucosides to their aglycones. The ratio of metabolism from glucoside to aglycone was different in each strain. Contrary to the facultative anaerobes, some of the obligate anaerobes did not metabolize soy isoflavone glucosides at all. Both the aerobic bacteria hardly metabolized soy isoflavone glucosides. The bacterial growth speed might show good correlation to the metabolizing speed of both glucosides. Therefore, the speed of metabolism would be different in each bacterial strain, too.

Soy food consumption does not lower LDL cholesterol in either equol or nonequol producers

BACKGROUND

Health claims link soy protein (SP) consumption, through plasma cholesterol reduction, to a decreased risk of heart disease. Soy isoflavones (ISOs), particularly in individuals who produce equol, might also contribute to lipid lowering and thus reduce SP requirements.

OBJECTIVE

The objective was to examine the contributions of SP, ISOs, and equol to the hypocholesterolemic effects of soy foods.

DESIGN

Nonsoy consumers (33 men, 58 women) with a plasma total cholesterol (TChol) concentration >5.5 mmol/L participated in a double-blind, placebo-controlled, crossover intervention trial. The subjects consumed 3 diets for 6 wk each in random order, which consisted of foods providing a daily dose of 1) 24 g SP and 70-80 mg ISOs (diet S); 2) 12 g SP, 12 g dairy protein (DP), and 70-80 mg ISOs (diet SD); and 3) 24 g DP without ISOs (diet D). Fasting plasma TChol, LDL cholesterol, HDL cholesterol, and triglycerides (TGs) were measured after each diet.

RESULTS

TChol was 3% lower with the S diet (-0.17 +/- 0.06 mmol/L; P < 0.05) than with the D diet, and TGs were 4% lower with both the S (-0.14 +/- 0.05 mmol/L; P < 0.05) and SD (-0.12 +/- 0.05 mmol/L; P < 0.05) diets. There were no significant effects on LDL cholesterol, HDL cholesterol, or the TChol:HDL cholesterol ratio. On the basis of urinary ISOs, 30 subjects were equol producers. Lipids were not affected significantly by equol production.

CONCLUSIONS

Regular consumption of foods providing 24 g SP/d from ISOs had no significant effect on plasma LDL cholesterol in mildly hypercholesterolemic subjects, regardless of equol-producing status.

Effects of isoflavone supplements vs. soy foods on blood concentrations of genistein and daidzein in adults

The objective of this investigation was to examine the pharmacokinetics of isoflavone concentrations over a 24-h period among healthy adults consuming either soy foods or soy isoflavone tablets at different doses. This randomized, cross-over trial was conducted with 12 generally healthy adults. The three phases of the intervention included isoflavone tablets at (1) 144 mg/day or (2) 288 mg/day and (3) soy foods designed to provide a calculated 96 mg isoflavones/day (doses in aglycone equivalents). Doses were spread out over three meals per day. After 6 days on each study phase, plasma isoflavone concentrations were determined on the seventh day at 0, 4, 8, 10, 12 and 24 h. Average levels of total isoflavone concentrations at 8, 10 and 12 h were >4 micromol/L for the soy food phase and for the higher dose tablet phase. Genistein concentrations were higher overall in the soy food vs. both the lower and the higher dose supplement phases of the study (P<.05). When comparing plasma concentrations for the two doses of tablets, saturation appeared more evident for genistein than for daidzein at the higher dose level. In conclusion, we observed important differences in the pharmacokinetics of genistein and daidzein contrasting the sources and doses of isoflavones when administered three times daily, including a possible advantage for increasing serum concentrations of isoflavones from consuming soy foods relative to isoflavone supplements.

The key importance of soy isoflavone bioavailability to understanding health benefits

Research over the past two decades has provided significant epidemiological and other evidence for the health benefits of the consumption of soy-based foods. A large number of dietary intervention studies have examined the effects of soy isoflavones on risk factors for cardiovascular disease and hormone-dependent cancers. However, these report large variability in outcome measures, very limited reproducibility between studies, and in some cases, controversy between the results of clinical trials using dietary soy or soy protein and isoflavone supplementation. This highlights a major gap in our understanding of soy isoflavone uptake, metabolism, distribution, and overall bioavailability. There are many potential factors that may influence bioavailability and a better knowledge is necessary to rationalize the inconsistencies in the intervention and clinical studies. This review focuses attention on our current state of knowledge in this area and highlights the importance of metabolism of the parent soy isoflavones and the critical role of gut microbiota on the bioavailability of these compounds and their metabolites.

Natural compounds with proteasome inhibitory activity for cancer prevention and treatment

The proteasome is a multicatalytic protease complex that degrades most endogenous proteins including misfolded or damaged proteins to ensure normal cellular function. The ubiquitin-proteasome degradation pathway plays an essential role in multiple cellular processes, including cell cycle progression, proliferation, apoptosis and angiogenesis. It has been shown that human cancer cells are more sensitive to proteasome inhibition than normal cells, indicating that a proteasome inhibitor could be used as a novel anticancer drug. Indeed, this idea has been supported by the encouraging results of the clinical trials using the proteasome inhibitor Bortezomib (Velcade, PS-341), a drug approved by the US Food and Drug Administration (FDA). Several natural compounds, including the microbial metabolite lactacystin, green tea polyphenols, and traditional medicinal triterpenes, have been shown to be potent proteasome inhibitors. These findings suggest the potential use of natural proteasome inhibitors as not only chemopreventive and chemotherapeutic agents, but also tumor sensitizers to conventional radiotherapy and chemotherapy. In this review, we will summarize the structures and biological activities of the proteasome and several natural compounds with proteasome inhibitory activity, and will discuss the potential use of these compounds for the prevention and treatment of human cancers.

Oral antibiotics decrease urinary isoflavonoid excretion in children after soy consumption

How oral antibiotics (OABX) alter isoflavones (IFLs) in soy-consuming children is unknown. We evaluated OABX effects on urinary IFL excretion rates (UIERs) in 17 children, ages 4 to 17 yr, who provided 2 urine collections in pairs of a baseline urine and an overnight urine collection after consuming a body-weight-adjusted dose of soy nuts. The first collection was during OABX treatment for a bacterial infection and the second when healthy and off antibiotics. IFL food levels and UIERs were measured for nonmetabolites (NM), namely, daidzein, genistein (GE), and glycitein, and the metabolites (M) dihydrodaidzein, dihydrogenistein, equol, and O-desmethylangolensin (DMA), by liquid chromatography mass spectrometry. Urinary IFLs were hypothesized to change after OABX due to intestinal microflora alterations. A total of 11 children completed the study correctly. During OABX use, UIER (nmol/h/kg) for GE (6.4 +/- 1.0 vs. 10.1 +/- 1.6), all NM (27.5 +/- 4.8 vs. 36.2 +/- 4.7), and total IFLs (all NM + all M; 29.4 +/- 5.0 vs. 38.8 +/- 4.8) was reduced (P < 0.05) vs. when healthy. In contrast, a trend toward more DMA production during OABX was observed (1.2 +/- 0.6 vs. 0.4 +/- 0.3, P = 0.13). The reduction in urinary IFL appearance could be due to the changes of intestinal bacteria by OABX and/or due to processes related to the infection.

Pharmacokinetics of the soybean isoflavone daidzein in its aglycone and glucoside form: a randomized, double-blind, crossover study

BACKGROUND

There are conflicting results in the literature on the bioavailability of isoflavones in the aglycone and the glucoside forms.

OBJECTIVE

The objective was to investigate the pharmacokinetics of the soy isoflavone daidzein (DAI) on oral administration of both the aglycone and glucoside form in a human intervention study. In addition, the pharmacokinetics of the bacterial and oxidative metabolites of DAI was assessed.

DESIGN

Seven German men aged 22-30 y participated in a randomized, double-blind study in a crossover design. After ingestion of pure DAI or pure daidzein-7-O-beta-d-glucoside (DG) (1 mg DAI aglycone equivalent/kg body weight), blood samples were drawn before isoflavone administration and 1, 2, 3, 4.5, 6, 8, 10, 12, 24, and 48 h after the dose. Urine was collected before and 0-6, 6-12, and 12-24 h after the intake of the isoflavones. The concentrations of DAI and its major bacterial and oxidative metabolites in plasma and urine were measured with isotope dilution capillary gas chromatography-mass spectrometry.

RESULTS

The systemic bioavailability (area under the curve; AUC(inf)), the maximal plasma concentration (C(max)), and the cumulative recovery of DAI in urine after administration of DG were 3-6 times greater than after the ingestion of DAI. Except for equol, which was formed by only one volunteer, all other quantified metabolites exhibited 2-12 times greater AUC(inf), C(max), and urinary recoveries after consumption of DG.

CONCLUSION

Our results show that DG exhibits a greater bioavailability than its aglycone when ingested in an isolated form.

Plasma Isoflavone Level and Subsequent Risk of Breast Cancer Among Japanese Women: A Nested Case-Control Study From the Japan Public Health Center-Based Prospective Study Group

Purpose

Because they have large variations in consumption, Asian countries are suitable settings for studies of the effect of relatively high-dose isoflavone intake on breast cancer risk. Nevertheless, no prospective study from Asia has assessed blood or urine levels as biomarkers of isoflavone intake.

Patients and Methods

A total of 24,226 women ages 40 to 69 years in the Japan Public Health Center–based prospective study who responded to the baseline questionnaire and provided blood in 1990 to 1995 were observed to December 2002. During a mean 10.6 years of follow-up, 144 patients newly diagnosed with breast cancer were identified. Two matched controls for each patient were selected from the cohort. Isoflavone levels were assessed by plasma level and food frequency questionnaire, and the odds ratio of breast cancer according to isoflavone level was estimated using a conditional logistic regression model.

Results

We found a statistically significant inverse association between plasma genistein and risk of breast cancer, but no association for plasma daidzein. Adjusted odds ratios for the highest versus lowest quartile of plasma level were 0.34 for genistein (95% CI, 0.16 to 0.74; P for trend, .02) and 0.71 for daidzein (95% CI, 0.35 to 1.44; P for trend, .54). Median plasma genistein values in the control group were 31.9 ng/mL for the lowest and 353.9 ng/mL for the highest quartile groups. Regarding dietary intake of isoflavones, nonsignificant inverse associations were observed for both genistein and daidzein.

Conclusion

This nested case-control study found an inverse association between plasma genistein and the risk of breast cancer in Japan.

Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials

OBJECTIVE

To clarify the effects of isoflavone intake on bone resorption and bone formation.

METHODS

We identified randomized controlled trials related to urinary deoxypyridinoline (Dpyr, a bone resorption marker) and serum bone-specific alkaline phosphatase (BAP, a bone formation marker) listed on MEDLINE (January 1966-April 2006), the Cochrane Controlled Trials Register, EMBASE (1985-January 2006), Science Citation Index and PUBMED (updated till April 2006).

RESULTS

Nine studies with a total of 432 subjects were selected for meta-analysis. The urinary Dpyr concentration in subjects who consumed isoflavones decreased significantly by -2.08 nmol/mmol (95% confidence interval (CI): -3.82 to -0.34 nmol/mmol) in comparison with that in subjects who did not consume isoflavones. Isoflavone intake vs placebo intake significantly increased serum BAP by 1.48 microg/l (95% CI: 0.22-2.75 mug/l). Decreases in the urinary Dpyr concentration with isoflavone intake of <90 mg/day and with treatment lasting less than 12 weeks were -2.34 nmol/mmol (95% CI: -4.46 to -0.22 nmol/mmol) and -2.03 nmol/mmol (95% CI: -3.20 to -0.85 nmol/mmol), respectively.

CONCLUSIONS

Isoflavone intervention significantly inhibits bone resorption and stimulates bone formation. These favorable effects occur even if <90 mg/day of isoflavones are consumed or the intervention lasts less than 12 weeks.

Higher bioavailability of isoflavones after a single ingestion of a soya-based supplement than a soya-based food in young healthy males

Soya isoflavones, genistein and daidzein, are the focus of numerous studies investigating their potential effects on health and results remain controversial. Bioavailability is clearly a crucial factor influencing their bioefficacy and could explain these discrepancies. This study aimed at assessing: (1) the isoflavone content of sixty-nine European soya-derivative products sold on the French market; (2) the bioavailability of isoflavones comparing supplement with food. Twelve healthy volunteers were recruited in a randomized two-way crossover trial and received 35 mg isoflavones equivalent aglycone either through supplements or through cheese, both containing different patterns of isoflavone conjugates and different daidzein:genistein ratios. A specific ELISA method was used to assess the plasma and urinary concentrations of isoflavones and thus the pharmacokinetic parameters, which were then normalized to mg of each isoflavone ingested. Results showed that the normalized Cmax of daidzein (P = 0.002) and similarly the normalized AUC0 --> infinity and Cmax of genistein (P = 0.002) from soya-based capsules were higher than that from soya-based cheese. In conclusion, this work completes studies on isoflavone bioavailability and presents new data regarding isoflavone concentrations in soya-derivative products. Assuming that isoflavone conjugation patterns do not influence isoflavone bioavailability, this study shows that isoflavones contained in capsules are more bioavailable than those contained in soya-based cheese. Although the supplement is more bioavailable, the relative importance of this is difficult to interpret as there is little evidence that supplements are biologically active in human subjects to date and further studies will be necessary for this specific supplement to prove its efficacy.

Endocrine disruptors and spontaneous premature labor: a case control study

BACKGROUND

Premature labor is a poorly understood condition. Estrogen is thought to play a key role and therefore the labor process may be affected by endocrine disruptors. We sought to determine whether or not an environmental toxicant, DDE, or dietary derived endocrine disruptors, daidzein and genistein, are associated with spontaneous preterm labor.

METHODS

Cases were defined as primiparous patients having a preterm delivery at or before 35 weeks following the spontaneous onset of labor. Controls were defined as primiparous women who delivered on the same day as the cases but at term gestation. Over approximately 1 year, 26 cases and 52 controls were recruited. Subjects agreed to have blood tests on day one postpartum for DDE and for the phytoestrogens genistein and daidzein.

RESULTS

The mean concentration of DDE was similar in the case and control groups: 4.29 vs 4.32 ng/g lipid p = .85. In the case group, 13/26 had detectable levels of daidzein (range 0.20 - 1.56 ng/ml) compared to 25/52 controls (range 0.21 - 3.26 ng/ml). The mean concentration of daidzein was similar in cases compared to controls: 0.30 vs .34 ng/ml p = 0.91. Of the case group,14/26 had detectable levels of genistein (range 0.20 - 2.19 ng/ml) compared to 32/52 controls (range 0.21 - 2.55 ng/ml). The mean concentration of genistein was similar in cases compared to controls: 0.39 vs 0.31 ng/ml, p = 0.61.

CONCLUSION

The serum levels of DDE in this population were found to be low. There appears to be no relationship between serum concentrations of DDE, daidzein, and genistein and spontaneous preterm labor in our population. The inability to identify an effect may be related to the comparatively low concentrations of DDE in our population and the rapid and variable reduction of phytoestrogens from women in labor.

Pasta naturally enriched with isoflavone aglycons from soy germ reduces serum lipids and improves markers of cardiovascular risk

Most studies of soy and cholesterol have tested foods made from purified soy proteins containing mainly isoflavone glycosides. Fermented soy foods have mainly isoflavone aglycons and account for a high proportion of the soy protein source in Asia, where there is an inverse relationship between soy intake and serum cholesterol. The aim of this study was to compare a novel soy germ pasta, naturally enriched in isoflavone aglycons as a result of the manufacturing process, with conventional pasta for effects on serum lipids and other cardiovascular risk markers. In this randomized, controlled, parallel study design of 62 adults with hypercholesterolemia who consumed a Step II diet that included one 80-g serving/d of pasta, we measured serum lipids, high sensitivity C-reactive protein (hsCRP), urinary isoprostanes, and brachial artery flow-mediated vasodilatation at baseline and after 4 and 8 wk. The pasta delivered 33 mg of isoflavones and negligible soy protein and led to a serum isoflavone concentration of 222 +/- 21 nmol/L; 69% of subjects were equol producers. Soy germ pasta reduced serum total and LDL cholesterol by 0.47 +/- 0.13 mmol/L (P = 0.001) and 0.36 +/- 0.10 mmol/L (P = 0.002) more than conventional pasta, representing reductions from baseline of 7.3% (P = 0.001) and 8.6% (P = 0.002), respectively. Arterial stiffness (P = 0.003) and hsCRP (P = 0.03) decreased and improvements in all the above risk markers were greatest in equol producers. All measures returned to baseline when patients were switched to conventional pasta. In conclusion, pasta naturally enriched with isoflavone aglycons and lacking soy protein had a significant hypocholesterolemic effect beyond a Step II diet and improved other cardiovascular risk markers.

The bioavailability and disposition kinetics of genistein in cats

The absorption and disposition kinetics of the soy isoflavone genistein were determined in cats (n = 6). An oral dose of 100 mg/kg was administered, which has previously been demonstrated to be the minimum oral estrogenic dose, and was administered intravenously at a dose of 20 mg/kg, being the largest practical dose that could be safely administered. Plasma free, and total (conjugated + free) genistein concentrations were determined by HPLC following organic extraction. Noncompartmental analysis revealed a half-life of 21.67 +/- 7.9 h (free) and 9.95 +/- 2.7 h (conjugated), volume of distribution 31.94 +/- 10.38 L/kg (free) and 11.82 +/- 3.96 L/kg (conjugated) following intravenous administration. Following oral administration the half-lives were determined to be 17 +/- 4.8 h (free) and 8.56 +/- 4.65 h (conjugated), with tmax = 4.4 +/- 0.6 h (free) and 4.42 +/- 0.99 h (conjugated), and Cmax = 0.276 +/- 0.1 microg/mL (free) and 6.24 +/- 6.58 microg/mL (conjugated). Oral bioavailabilities were 1.379 +/- 0.9% (free) and 29.85 +/- 22.61% (conjugated). The ratio of total:free genistein ranged from 25.9 to 5.5. Poor oral absorption and efficient conjugation explain the low bioavailability of free genistein. Accumulation of genistein in peripheral lipophilic compartments may occur.

Intestinal bacteria metabolize the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine following consumption of a single cooked chicken meal in humans

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a carcinogenic heterocyclic amine formed in meats during cooking. Although the formation of PhIP metabolites by mammalian enzymes has been extensively reported, the involvement of the intestinal bacteria remains unclear. This study examined the urinary and fecal excretion of a newly identified microbial PhIP metabolite 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1) in humans. The subjects were fed 150 g of cooked chicken containing 0.88-4.7 microg PhIP, and urine and feces collections were obtained during 72 h after the meal. PhIP-M1 and its trideuterated derivate were synthesized and a LC/MS/MS method was developed for their quantification. The mutagenic activity of PhIP-M1, as analyzed using the Salmonella strains TA98, TA100 and TA102, yielded no significant response. Of the ingested PhIP dose, volunteers excreted 12-21% as PhIP and 1.2-15% as PhIP-M1 in urine, and 26-42% as PhIP and 0.9-11% as PhIP-M1 in feces. The rate of PhIP-M1 excretion varied among the subjects. Yet, an increase in urinary excretion was observed for successive time increments, whereas for PhIP the majority was excreted in the first 24h. These findings suggest that besides differences in digestion, metabolism and diet, the microbial composition of the gastrointestinal tract also strongly influences individual disposition and carcinogenic risk from PhIP.

Can the combination of flaxseed and its lignans with soy and its isoflavones reduce the growth stimulatory effect of soy and its isoflavones on established breast cancer?

Consumption of phytoestrogen (PE)-rich foods (i. e., soy and flaxseed (FS)) is increasing because of their suggested health benefits. However, recent studies raise concern over the safety of soy and its isoflavones, particularly genistein (GEN), for postmenopausal breast cancer (BC), due to their potential stimulatory effects on human breast tissue and on the growth of existing tumors in rodents. FS, rich in PE lignans, which is metabolized to the mammalian lignans enterolactone (ENL) and enterodiol (END), has consistently been shown to have tumor inhibitory effects in a human clinical trial as well as rodent BC models. Using the preclinical athymic mouse postmenopausal BC model, combining FS with soy protein or GEN with END and ENL, was found to negate the tumor stimulatory effects of soy protein or GEN alone. The mechanism may be related to the modulation of estrogen receptor and MAPK signaling pathways. If these studies can be confirmed in clinical trials, then consumption of combined soy and FS, or their PEs, may reduce the tumor growth stimulatory effect of soy or GEN. This may indicate that if soy is consumed with lignan-rich foods, it may continue to induce its other beneficial health effects, without inducing adverse effect on postmenopausal BC.

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.

Natural polyphenol disposition via coupled metabolic pathways

A major challenge associated with the development of chemopreventive polyphenols is the lack of bioavailability in vivo, which are primarily the result of coupled metabolic activities of conjugating enzymes and efflux transporters. These coupling processes are present in disposition tissues and organs in mammals and are efficient for the purposes of drug metabolism, elimination and detoxification. Therefore, it was expected that these coupling processes represent a significant barrier to the oral bioavailabilities of polyphenols. In various studies of this coupling process, it was identified that various conjugating enzymes such as uridine 5'-diphosphate-glucuronosyltransferase and sulfotransferase are capable of producing very hydrophilic metabolites of polyphenols, which cannot diffuse out of the cells and needs the action of efflux transporters to pump them out of the cells. Additional studies have shown that efflux transporters, such as multi-drug resistance-associated protein 2, breast cancer-resistant protein and the organic anion transporters, appear to serve as the gate keeper when there is an excess capacity to metabolise the compounds. These efflux transporters may also act as the facilitator of metabolism when there is a product/metabolite inhibition. For polyphenols, these coupled processes enable a duo recycling scheme of enteric and enterohepatic recycling, which allows the polyphenols to be reabsorbed and results in longer than expected apparent plasma half-lifes for these compounds and their conjugates. Because the vast majority of polyphenols in plasma are hydrophilic conjugates, more research is needed to determine if the metabolites are active or reactive, which will help explain their mechanism of actions.

Dietary isoflavones differentially induce gene expression changes in lymphocytes from postmenopausal women who form equol as compared with those who do not

Human and animal studies suggest that dietary soy isoflavones reduce cancer risk, ameliorate postmenopausal syndrome and decrease bone resorption in postmenopausal women. The capacity to form the metabolite equol from daidzein is suggested as an important modulator of response to isoflavones; this capacity depends on gut colonization with appropriate bacteria. We administered a dietary supplement containing high-dose purified soy isoflavones (genistein, 558 mg/day; daidzein, 296 mg/day; and glycitein, 44 mg/day) to 30 postmenopausal women for 84 days and collected peripheral lymphocytes at timed intervals. Using microarray analysis, we determined whether changes in gene expression associated with this treatment support existing hypotheses as to isoflavones' mechanisms of action. Expression of a large number of genes was altered by isoflavone treatment, including induction of genes associated with cyclic adenosine 3',5'-monophosphate (cAMP) signaling and cell differentiation and decreased expression of genes associated with cyclin-dependent kinase activity and cell division. We report that isoflavone treatment in subjects who have the capacity to produce equol differentially affects gene expression as compared with nonproducers, supporting the plausibility of the importance of equol production. In general, isoflavones had a stronger effect on some putative estrogen-responsive genes in equol producers than in nonproducers. Our study suggests that, in humans, isoflavone changes are related to increased cell differentiation, increased cAMP signaling and G-protein-coupled protein metabolism and increased steroid hormone receptor activity and have some estrogen agonist effects; equol-production status is likely to be an important modulator of responses to isoflavones.

Phytoestrogens levels determination in the cord blood from Malaysia rural and urban populations

This study is a result of an analysis of free and conjugated phytoestrogens daidzein, genistein, daidzin, genistin and coumesterol in human cord blood plasma using LCMS. Cord blood was collected from urban and rural populations of Malaysia (n=300) to establish a simple preliminary database on the levels of the analyzed compounds in the collected samples. The study also aimed to look at the levels of phytoestrogens in babies during birth as this may have a profound effect on the developmental process. The sample clean up was carried out by solid-phase extraction using C18 column and passed through DEAE sephadex gel before analysis by LCMS. The mean concentrations of total phytoestrogens were daidzein (1.4+/-2.9 ng/ml), genistein (3.7+/-2.8 ng/ml), daidzin (3.5+/-3.1 ng/ml), genistin (19.5+/-4.2 ng/ml) and coumesterol (3.3+/-3.3 ng/ml). Distribution of phytoestrogen was found to be higher in samples collected from rural areas compared to that of urban areas.

Urinary isoflavone kinetics: the effect of age, gender, food matrix and chemical composition

Urinary isoflavone excretion is used to monitor compliance and examine biological effects. The present study determined if there were alterations in urinary isoflavone excretion following the ingestion of different soya foods and if age and gender potentially modified profiles. Twenty premenopausal women, seventeen post-menopausal women and twenty men received a defined single oral bolus dose (0·44mg isoflavones/kg body weight) of soya milk, textured vegetable protein (TVP) or tempeh on three separate occasions. Baseline and four consecutive complete 24h pooled urines were collected during each period. Urinary genistein recovery was influenced by gender and food matrix. For women the urinary genistein recovery was higher following soya-milk consumption compared with TVP (P<0·05). Tempeh consumption also resulted in an increased urinary genistein recovery relative to soya milk in premenopausal women (P<0·052). No differences in urinary genistein recoveries between soya foods were observed in the men. Although urinary daidzein excretion was similar across the foods studied and was not affected by age or gender, conversion to its intestinal metabolite, equol, resulted in potential matrix and chemical composition effects; urinary equol excretion was higher (P<0·01) following tempeh ingestion among equol producers. Together these data suggest that the fractional absorption of genistein is potentially different in men and women and is influenced by the food matrix and chemical composition. Furthermore, the data suggest that the metabolism of daidzein may be altered by the chemical composition of the isoflavones ingested. Further studies are required to examine the effect of higher intake and define the relative influence of these factors in elderly population groups.

Validation of a phytoestrogen food frequency questionnaire with urinary concentrations of isoflavones and lignan metabolites in premenopausal women

OBJECTIVE

The purpose of this study was to examine the association between dietary intake of phytoestrogens estimated by a food frequency questionnaire (FFQ) with urinary metabolites.

METHODS

Participants were 26 premenopausal, Caucasian women aged 25 to 42 years. Dietary intake of isoflavones (genistein and daidzein) and lignans (secoisolariciresinol and matairesinol) were estimated by a 53-item interviewer-administered FFQ on two occasions, reflecting 'habitual' (previous 2 months) and 'recent' (previous 2 days) dietary intake. Isoflavone (genistein, daidzein) and lignan (enterolactone, enterodiol and secoisolariciresinol) concentrations were measured in 24-hour urine samples by gas chromatography-mass spectrometry. Correlations between FFQ (habitual and recent, separately) and urinary metabolite values were assessed using Spearman correlation coefficients.

RESULTS

Mean habitual isoflavone and lignan intakes were 13.7 mg/day and 13.8 mg/day, respectively. Mean urinary concentrations of isoflavones and lignans were 17.4 micromol/day and 20.6 micromol/day, respectively. Recent and habitual isoflavone intakes were correlated with urinary excretion of metabolites (r = 0.64, p < 0.001 and r = 0.54, p = 0.004, respectively). Urinary excretion of lignans was also modestly correlated with recent and habitual lignan intakes (r = 0.46, p = 0.02 and r = 0.40, p = 0.05, respectively).

CONCLUSIONS

Our results support the use of this FFQ as a measure of dietary isoflavone and lignan intake in epidemiological studies.

Does an apple a day keep the doctor away because a phytoestrogen a day keeps the virus at bay? A review of the anti-viral properties of phytoestrogens

From dengue to herpes and influenza to AIDS, the phytoestrogens that are present in many fruits and vegetables have been shown to exert anti-viral properties. Here we review the various different anti-viral mechanisms employed by phytoestrogens.

Estimated Asian adult soy protein and isoflavone intakes

There is substantial interest in the possible anticancer effects of soy foods. In part, this is because of the historically low incidence rates of breast and prostate cancer in Asia. Of the several putative soybean chemopreventive agents, isoflavones have received the most attention. Awareness of this research has led increasing numbers of consumers to use soy foods, isoflavone-fortified foods, and isoflavone supplements. Therefore, there is a need for guidance regarding appropriate isoflavone intake levels. To this end, this article analyzed soy protein (as a surrogate for isoflavones) and isoflavone intake of the major soy food-consuming countries using individual dietary surveys for the bulk of the information. In total, 24 surveys from 4 countries that met the inclusion criteria were identified: Japan (n = 11), China (n = 7), Hong Kong (n = 4), and Singapore (n = 2). The results indicate that older Japanese adults consume approximately 6-11 g of soy protein and 25-50 mg of isoflavones (expressed as aglycone equivalents) per day. Intake in Hong Kong and Singapore is lower than in Japan, whereas significant regional intake differences exist for China. Evidence suggests that < or =10% of the Asian population consumes as much as 25 g of soy protein or 100 mg of isoflavones per day. The applicability of these findings for making soy intake recommendations for non-Asians is discussed.

Frequency of soy food consumption and serum isoflavone concentrations among Chinese women in Shanghai

Objective:

The food-frequency questionnaire (FFQ) can be an efficient tool to evaluate dietary intake in large, population-based studies, especially for specific foods. The objective of this study was to validate the assessment of soy and isoflavone (daidzein and genistein) intakes, measured by an FFQ, by comparing intakes with serum isoflavone concentrations.

Design and setting:

Soy and isoflavone intakes and serum isoflavone concentrations were determined as part of a case–control study of dietary factors and risks of benign breast disease and breast cancer. The FFQ, administered during an in-person interview, included six soy-specific line items. Blood was drawn within one week of FFQ completion.

Subjects:

In total, 1823 women living in Shanghai, People's Republic of China.

Results:

In this population, soybean milk, fresh bean curd and other bean foods were eaten once per week, and fermented bean curd, fried bean curd puff and soybeans were eaten less than once per week. A significant linear trend (P > 0.01) in serum isoflavone concentrations across increasing categories of soy and isoflavone intakes was observed, indicating that soy and isoflavone intakes, measured by the FFQ, well distinguished serum isoflavone concentrations. Linear trends were also observed in both case and control groups in stratified analyses, suggesting little differential bias by case–control status.

Conclusions:

The results suggest that the FFQ provides a useful marker of soy food consumption and isoflavone exposure in this population.

Bioavailability and urinary excretion of isoflavones in humans: effects of soy-based supplements formulation and equol production

Soy isoflavones (IF) are of particular interest for their possible estrogenic effects on the symptoms of menopause. The bioavailability of IF is clearly a factor influencing their biological activity. The first aim of this study was to elucidate the impact of the matrix process and especially the formulation of soy-based capsules on IF bioavailability. Twelve healthy volunteers were recruited for a randomized, double-blind, two-way crossover trial and received a single dose of the two soy-based formulations, one containing a pure soy standardized extract of IF, and the other containing soy flour in addition to the standardized extract of IF. Using a new and validated ELISA method, we measured the plasma and urinary concentrations of genistein, daidzein and its metabolite equol. Based on European Medicine Evaluation Agency recommendations, the main pharmacokinetic parameters allowed us to demonstrate the bioequivalence of the two formulations, indicating that the presence or absence of soy flour did not alter either the absorption or the elimination of daidzein and genistein. As bioequivalence was demonstrated, we pooled data collected during the two study-periods to address another original issue: Did the ability to produce equol affect the bioavailability of daidzein? We demonstrated that daidzein excretion was significantly lower in equol producers compared with equol non producers over the entire elimination period of the soy IF. This difference disappeared when equol excretion was added to daidzein excretion in equol producers. Our results indicated that the production of equol could partly explain the difference in daidzein bioavailability after IF ingestion.

Bioavailability of isoflavones after ingestion of soy beverages in healthy adults

It is unknown whether the bioavailability of isoflavones is affected by the concomitant ingestion of glucosides or aglycones. This study was designed to investigate the effects of soymilk-based beverages containing different types of isoflavones on their absorption, excretion, and metabolism. Twelve healthy volunteers consumed 3 kinds of soymilk: untreated soymilk, beta-glucosidase-treated soymilk, and fermented soymilk. Blood samples were collected after 0, 1, 2, 3, 4, 5, 6, 7, 8, and 24 h. Urine samples were collected from 0 to 48 h. Concentrations of isoflavones and daidzein metabolites in serum and urine were measured by liquid chromatography-mass spectrometry. After the ingestion of soymilk, the total concentration of isoflavones in serum rose slowly and reached a maximum of 0.94 +/- 0.39 micromol/L at 6.0 +/- 1.2 h. However, beta-glucosidase-treated soymilk and fermented soymilk increased the serum isoflavone concentration significantly more quickly with maximum concentrations at 1.0 h of 1.75 +/- 0.33 micromol/L and 2.05 +/- 0.32 micromol/L, respectively. The urinary excretion of isoflavones after ingesting of these aglycone-enriched preparations was significantly greater than after consumption of untreated soymilk up to 8 h after injection, but not thereafter. The total and individual concentrations of isoflavones in serum and urine did not differ when subjects consumed the 2 aglycone-enriched soymilks. However, in equol producers (n = 5), the ingestion of ESM tended to increase urinary excretion of equol compared with the consumption of FSM (P = 0.08). These results demonstrated that the isoflavone aglycones of soymilk were absorbed faster and in greater amounts than their glucosides in healthy adults and that the metabolism of isoflavones might be affected by the type of soymilk consumed.

Method of defining equol-producer status and its frequency among vegetarians

7-Hydroxy-3-(4'-hydroxyphenyl)-chroman (S-equol) is a specific end-metabolite formed in the biotransformation of the dietary soy isoflavones daidzin and daidzein by intestinal bacteria. The frequency of equol production varies among individuals and populations, and it is suggested that the efficacy of soy foods differs depending on the ability of an individual to produce equol. To develop a standardized approach to define equol-producer status that can be universally adopted to differentiate these 2 distinct populations, we measured isoflavones in serum and urine collected from a cohort of 41 healthy adults, comprising 29 vegetarians and 12 nonvegetarians, after consuming 2 x 250 mL/d soy milk on 3 consecutive days. Serum and urinary daidzein and S-equol concentrations were analyzed by MS. Serum S-equol and daidzein concentrations ranged from 10.3-139 nmol/L (2.5-33.6 microg/L) and 16-1401 nmol/L (4.0-356 microg/L), respectively, whereas in urine the corresponding concentrations ranged from 16-12,574 nmol/L (4-3043 microg/L) and 539-26,834 nmol/L (137-6816 microg/L), respectively. The log10-transformed urinary S-equol:daidzein ratio provided a clearer distinction of equol-producer status than the absolute serum or urinary S-equol concentrations because it is independent of isoflavone intake and minimizes interindividual variation in isoflavone pharmacokinetics or differences in analytical methodologies. A threshold value for the log10-transformed urinary S-equol:daidzein ratio of -1.75 provided a demarcation to define equol-producer status. The frequency of equol producers in the vegetarians was 59%, similar to the reported frequency in Japanese adults consuming soy, and much higher than for nonvegetarian adults (25%), suggesting that dietary components other than soy influence S-equol synthesis by intestinal bacteria.