Altered kinetics and extent of urinary daidzein and genistein excretion in women during chronic soya exposure

Application of a skin and liver Chip2 microphysiological model to investigate the route-dependent toxicokinetics and toxicodynamics of consumer-relevant doses of genistein

The HUMMIC skin-liver Chip2 microphysiological system using EpiDerm™ and HepaRG and stellate liver spheroids was used to evaluate the route-specific metabolism and toxicodynamic effects of genistein. Human-relevant exposure levels were compared: 60 nM representing the plasma concentration expected after topical application of a cosmetic product and 1 μM representing measured plasma concentrations after ingesting soya products. Genistein was applied as single and repeated topical and/or systemic doses. The kinetics of genistein and its metabolites were measured over 5 days. Toxicodynamic effects were measured using transcriptional analyses of skin and liver organoids harvested on Days 2 and 5. Route-specific differences in genistein's bioavailability were observed, with first-pass metabolism (sulfation) occurring in the skin after topical application. Only repeated application of 1 μM, resembling daily oral intake of soya products, induced statistically significant changes in gene expression in liver organoids only. This was concomitant with a much higher systemic concentration of genistein which was not reached in any other dosing scenario. This suggests that single or low doses of genistein are rapidly metabolised which limits its toxicodynamic effects on the liver and skin. Therefore, by facilitating longer and/or repeated applications, the Chip2 can support safety assessments by linking relevant gene modulation with systemically available parent or metabolite(s). The rate of metabolism was in accordance with the short half-life observed in in vivo in humans, thus supporting the relevance of the findings. In conclusion, the skin-liver Chip2 provides route-specific information on metabolic fate and toxicodynamics that may be relevant to safety assessment.

Soy isoflavones decrease fibroglandular breast tissue measured by magnetic resonance imaging in premenopausal women: A 2-year randomized double-blind placebo controlled clinical trial

BACKGROUND & AIMS

Populations consuming soy have reduced risk for breast cancer, but the mechanisms are unclear. We tested the hypothesis that soy isoflavones, which have ovarian hormone-like effects, can reduce fibroglandular breast tissue (FGBT, 'breast density'), a strong risk marker for breast cancer.

METHODS

Premenopausal women (age 30-42 years) were randomized to consume isoflavones (136.6 mg as aglycone equivalents, n = 99) or placebo (n = 98) for 5 days per week up to 2 years, and changes in breast composition measured by magnetic resonance imaging at baseline and yearly intervals were compared after square root transformation using linear mixed effects regression models.

RESULTS

By intention-to-treat analyses (n = 194), regression coefficients (β estimates) of the interaction of time and isoflavone treatment were -0.238 (P = 0.06) and -0.258 (P < 0.05) before and after BMI adjustment, respectively for FGBT, 0.620 (P < 0.05) and 0.248 (P = 0.160), respectively for fatty breast tissue (FBT), and -0.155 (P < 0.05) and -0.107 (P < 0.05), respectively for FGBT as percent of total breast (FGBT%). β Estimates for interaction of treatment with serum calcium were -2.705 for FBT, and 0.588 for FGBT% (P < 0.05, before but not after BMI adjustment). BMI (not transformed) was related to the interaction of treatment with time (β = 0.298) or with calcium (β = -1.248) (P < 0.05). Urinary excretion of isoflavones in adherent subjects (n = 135) significantly predicted these changes in breast composition. Based on the modeling results, after an average of 1.2, 2.2 and 3.3 years of supplementation, a mean decrease of FGBT by 5.3, 12.1, and 19.3 cc, respectively, and a mean decrease of FGBT% by 1.37, 2.43, and 3.50%, respectively, were estimated for isoflavone exposure compared to placebo treatment. Subjects with maximum isoflavone excretion were estimated to have 38 cc less FGBT (or ∼3.13% less FGBT%) than subjects without isoflavone excretion. Decrease in FGBT and FGBT% was more precise with daidzein than genistein.

CONCLUSIONS

Soy isoflavones can induce a time- and concentration-dependent decrease in FGBT, a biomarker for breast cancer risk, in premenopausal women, and moderate effects of calcium on BMI and breast fat, suggesting a beneficial effect of soy consumption.

TRIAL REGISTRATION

www.

CLINICALTRIALS

gov identifier: NCT00204490.

TRIAL REGISTRATION

www.

CLINICALTRIALS

gov identifier: NCT00204490.

Fluoride Exposure from Soybean Beverage Consumption: A Toxic Risk Assessment

The consumption of vegetable milk as a substitute for cow's milk has increased in recent years. Of all the vegetable beverages on the market, soy is the most widely consumed. Soy is exposed to contamination by different chemical elements during harvesting. In this study, the concentration of fluoride in soy beverages was analyzed. Fluoride is an element that in high concentrations can be toxic, causing dental and bone fluorosis. The aims of the study were (i) to analyze the fluoride concentration in 30 samples in the most popular brands (A-Brand, B-Brand, C-Brand) of soybean beverages by a fluoride ion selective potentiometer and (ii) to evaluate the toxicological risk derived from its consumption. The fluoride concentrations were 15.5 mg/L (A-Brand), 11.3 mg/L (B-Brand) and 8.5 mg/L (C-Brand). A consumption of 1 to 3 servings/day was established. One serving (200 mL) of soybean beverage offered a contribution percentage over the ADI (acceptable daily intake) for infants and children. Teenagers and adults did not exceed the ADI (10 mg/day). The consumption of soy beverages contributes significantly to the daily intake of fluoride, which could exceed the ADI with a consequent health risk. It is recommended to control the fluoride levels in the raw material and in the final product to assure the safety of these products.

(Poly)phenolic compounds and gut microbiome: new opportunities for personalized nutrition

For decades, (poly)phenols have been linked to cardiometabolic health, but population heterogeneity limits their apparent efficacy and the development of tailored, practical protocols in dietary interventions. This heterogeneity is likely determined by the existence of different metabotypes, sub-populations of individuals metabolizing some classes of (poly)phenols differently. The gut microbiota plays a major role in this process. The impact of microbiota-related phenolic metabotypes on cardiometabolic health is becoming evident, although the picture is still incomplete, and data are absent for some classes of (poly)phenols. The lack of a complete understanding of the main microbial actors involved in the process complicates the picture. Elucidation of the mechanisms behind phenolic metabotypes requires novel experimental designs that can dissect the inter-individual variability. This paper, in addition to providing an overview on the current state-of-the-art, proposes wider metabotyping approaches as a means of paving the way towards effective personalized nutrition with dietary (poly)phenols.

Soy isoflavones interact with calcium and contribute to blood pressure homeostasis in women: a randomized, double-blind, placebo controlled trial

BACKGROUND

Estrogens and calcium regulate vascular health but caused adverse cardiovascular events in randomized trials.

OBJECTIVES

Whether phytoestrogenic soy isoflavones modulate the physiological effects of calcium on blood pressure was explored.

DESIGN

A double-blind, randomized study assigned 99 premenopausal women to 136.6 mg isoflavones (as aglycone equivalents) and 98 to placebo for 5 days per week for up to 2 years. Blood pressure, serum calcium and urinary excretion of daidzein (DE) and genistein (GE) were measured repeatedly before and during treatment.

RESULTS

Isoflavones did not affect blood pressure per intake dose assignment (i.e. intention-to-treat, n = 197), but significantly affected blood pressure per measured urinary excretion of isoflavones (i.e. per protocol analysis, n = 166). Isoflavones inversely moderated calcium effects on systolic blood pressure (SBP) (interaction term β-estimates: - 3.1 for DE, - 12.86 for GE, all P < 0.05), and decreased diastolic blood pressure (DBP) (β-estimates: - 0.84 for DE, - 2.82 for GE, all P < 0.05) after controlling for calcium. The net intervention effects between the maximum and no isoflavone excretion were - 17.7 and + 13.8 mmHg changes of SBP, respectively, at serum calcium of 10.61 and 8.0 mg/dL, and about 2.6 mmHg decrease of DBP.

CONCLUSIONS

Moderation by isoflavones of the physiological effect of calcium tends to normalize SBP, and this effect is most significant when calcium concentrations are at the upper and lower limits of the physiological norm. Isoflavones decrease DBP independent of calcium levels. Further studies are needed to assess the impact of this novel micronutrient effect on blood pressure homeostasis and cardiovascular health.

TRIAL REGISTRATION

www.clinicaltrials.gov identifier: NCT00204490.

Daidzein and genistein have differential effects in decreasing whole body bone mineral density but had no effect on hip and spine density in premenopausal women: A 2-year randomized, double-blind, placebo-controlled study

Soy isoflavones are potentially beneficial phytoestrogens, but their tissue-selective effects in women are poorly understood. We tested the hypothesis that soy isoflavones affect bone mineral density (BMD), which may be influenced by individual differences in isoflavone metabolism and serum calcium levels. Ninety-nine healthy premenopausal women were randomized to isoflavones (136.6 mg aglycone equivalence) and 98 to placebo for 5 days per week for up to 2 years. BMD, serum calcium, and urinary excretion of daidzein and genistein were measured before and during treatment. In 129 adherent subjects, we found that isoflavone exposure, determined by urinary excretion levels, but not by dose assignment, interacted with serum calcium in affecting whole body BMD, but not hip and spine BMD. The regression coefficient was -0.042 for genistein excretion (GE) and 0.091 for the interaction between GE and serum calcium (all P < .05). Daidzein excretion had similar but marginal effect. Genistein significantly decreased whole body BMD only at low normal serum calcium levels but increased whole body BMD at higher serum calcium levels. Comparing maximum to minimum GE, mean changes in whole body BMD were +0.033 and -0.113 g/cm² at serum calcium levels of 10 and 8.15 mg/dL, respectively. These associations were not evident by intention-to-treat analysis, which could not model for inter-individual differences in isoflavone metabolism. In summary, soy isoflavones decrease whole body BMD only when serum calcium is low. Isoflavones are dietary substances that may influence calcium homeostasis by releasing calcium from bone while sparing the common fracture risk sites hip and spine.

Novel effects of phytoestrogenic soy isoflavones on serum calcium and chloride in premenopausal women: A 2-year double-blind, randomized, placebo-controlled study

BACKGROUND

Soy phytoestrogens are potential alternatives to postmenopausal hormone replacement therapy (HRT). Adverse effects of HRT such as myocardial infarction, stroke, and pulmonary embolism are mediated by calcium-induced signaling.

OBJECTIVE

To determine whether soy isoflavones affect serum calcium in healthy female subjects.

DESIGN

In a double-blind trial, 197 premenopausal women were randomly assigned to either isoflavone (N = 99) or placebo pills (N = 98) 5 days per week for up to 2 years, plus prenatal vitamins. Isoflavone pills contained 60 mg genistein, 60 mg daidzein and 16.6 mg glycitein (expressed as aglycone equivalents). All pills contained 15 mg riboflavin as an adherence marker. Blood chemistries and urinary daidzein, genistein and riboflavin were measured multiple times during the luteal phase before and during treatment.

RESULTS

Analysis of the adherent population (N = 83 per group), revealed significantly strong associations between urinary levels of isoflavones and serum concentrations of calcium (regression coefficients 0.082 for daidzein and 0.229 for genistein, all P < 0.01) and chloride (regression coefficient, -1.537 for genistein, P < 0.0001), mediated in part by albumin. The effects amounted to mean changes of +0.24 mg/dL for calcium and -1.45 mEq/L for chloride, with each visit for subjects excreting the most vs. the least amounts of isoflavones. These associations were not evident in the intention-to-treat analysis (N = 197) that did not assess expected variations in isoflavone levels within and between subjects from metabolism and adherence.

CONCLUSIONS

These novel and strong effects of soy isoflavones on calcium homeostasis have important implications for long term effects of these natural substances on cardiovascular diseases.

Biomarkers of legume intake in human intervention and observational studies: a systematic review

There is a growing interest in assessing dietary intake more accurately across different population groups, and biomarkers have emerged as a complementary tool to replace traditional dietary assessment methods. The purpose of this study was to conduct a systematic review of the literature available and evaluate the applicability and validity of biomarkers of legume intake reported across various observational and intervention studies. A systematic search in PubMed, Scopus, and ISI Web of Knowledge identified 44 studies which met the inclusion criteria for the review. Results from observational studies focused on soy or soy-based foods and demonstrated positive correlations between soy intake and urinary, plasma or serum isoflavonoid levels in different population groups. Similarly, intervention studies demonstrated increased genistein and daidzein levels in urine and plasma following soy intake. Both genistein and daidzein exhibited dose-response relationships. Other isoflavonoid levels such as O-desmethylangolensin (O-DMA) and equol were also reported to increase following soy consumption. Using a developed scoring system, genistein and daidzein can be considered as promising candidate markers for soy consumption. Furthermore, genistein and daidzein also served as good estimates of soy intake as evidenced from long-term exposure studies marking their status as validated biomarkers. On the contrary, only few studies indicated proposed biomarkers for pulses intake, with pipecolic acid and S-methylcysteine reported as markers reflecting dry bean consumption, unsaturated aliphatic, hydroxyl-dicarboxylic acid related to green beans intake and trigonelline reported as marker of peas consumption. However, data regarding criteria such as specificity, dose-response and time-response relationship, reliability, and feasibility to evaluate the validity of these markers is lacking. In conclusion, despite many studies suggesting proposed biomarkers for soy, there is a lack of information on markers of other different subtypes of legumes. Further discovery and validation studies are needed in order to identify reliable biomarkers of legume intake.

Riboflavin as an independent and accurate biomarker for adherence in a randomized double-blind and placebo-controlled clinical trial

BACKGROUND

Medication adherence is critical for success of clinical trials.

OBJECTIVE

To assess oral riboflavin is an adherence marker.

METHODS

Riboflavin was incorporated into active treatment and placebo pills for a clinical trial lasting for 2 years.

RESULTS

The accuracy (area under the receiver operating curve) of urinary riboflavin was 0.91 as a binary classifier of adherence, and was similar or better than for two active study ingredients daidzein (0.92) and genistein (0.87) (all p < 0.0001). Decreased adherence over time was similar in the two study groups.

CONCLUSION

Riboflavin is an accurate and useful biomarker for study pill ingestion.

Investigation of the interactions between Chrysanthemum morifolium flowers extract and intestinal bacteria from human and rat

Flos Chrysanthemi, dried flower of Chrysanthemum morifolium Ramat, has drawn much attention recently owing to its potential beneficial health effects for human. Flos Chrysanthemi products are usually taken orally and metabolized by intestinal microflora. However, there has been no investigation of the comprehensive metabolic profile of the Flos Chrysanthemi extract by intestinal flora owing to its chemical complexity and the limitations of analytical methods. In this paper, a rapid, sensitive and automated analysis method, ultra-performance liquid chromatography/quadrupole time of flight mass spectrometry including MS^E technology and automated data processing Metabolynx™ software, was developed and successfully applied for the biotransformation and metabolic profile of flavonoids in the Flos Chrysanthemi extract by intestinal flora from human and rat. A total of 32 metabolites were detected and tentatively identified in human and rat intestinal bacterial samples. These metabolites indicated that hydrolysis, hydroxylation, acetylation, methylation, hydrogenation and deoxygenation were the major conversion pathways of flavonoids in the Flos Chrysanthemi extract in vitro. Furthermore, the effects of the Flos Chrysanthemi extract on the growth of different intestinal bacteria were detected using an Emax precision microplate reader. Certain pathogenic bacteria such as Enterobacter, Enterococcus, Clostridium and Bacteroides were significantly inhibited by Flos Chrysanthemi, while commensal probiotics such as Lactobacillus and Bifidobacterium were moderately promoted. Our observation provided further evidence for the importance of intestinal bacteria in the metabolism and potential activity of the Flos Chrysanthemi extract. The results will also be helpful for the further pharmacokinetic study of Flos Chrysanthemi and to unravel how it works in vivo.

Absorption, distribution, metabolism, and excretion of isoflavonoids after soy intake

Soy is the major source of dietary exposure to isoflavonoids (IFLs). Accumulating evidence supports a role for soy and IFLs in the protection against many chronic diseases including cancer. After soy intake we found a biphasic IFL appearance pattern in plasma as well as in urine that we suggest to be due to IFL absorption in the small intestine (ca. 10%) during the first 2h after intake and IFL absorption in the large intestine (ca. 90%) 4-6 h after intake. While each IFL disappears from the circulation at different times excellent correlations between urinary and circulating IFL values were discovered and algorithms to convert urinary excretion values into circulating levels were established. We suggest the term 'apparent bioavailability' when using urinary data to describe IFL exposure. The IFL bioavailability was found to be influenced by gut bacteria, oral antibiotic treatment (OABX), and an individual's age and health status. While daidzein (DE) and genistein start to be absorbed minutes after intake, equol (EQ) appears in plasma only after a minimum of 8h following soy intake owing to the required transit time of DE to the colon where the conversion of DE to EQ takes place by intestinal microbiota. We have also shown that the apparent IFL bioavailability is higher in children than adults, higher in healthy versus non-healthy individuals, and decreased in children but increased in adults during OABX. Finally, we propose to use a urinary EQ/DE ratio of 0.018 with a DE threshold to identify EQ producers. With this cutoff definition we observed that EQ production is inconsistent over time in 5-30% of both premenopausal and postmenopausal women.

Effects of short-term fructooligosaccharide intake on equol production in Japanese postmenopausal women consuming soy isoflavone supplements: a pilot study

BACKGROUND

Recent studies suggest that some of the clinical effectiveness of soy or daidzein, which is a type of isoflavone, may be attributed to a person's ability to produce equol from daidzein. Equol, which is a metabolite of one of the major soybean isoflavones called daidzein, is produced in the gastrointestinal tract by certain intestinal microbiota where present. Habitual dietary patterns may alter the intestinal bacterial profile, and influence the metabolism of isoflavones and the production of equol. Fructooligosaccharides (FOS) have a prebiotic activity as well as being a dietary fibre. The purpose of the present study was to determine whether FOS supplementation increases equol production in equol producers and stimulates equol production in equol non-producers in Japanese postmenopausal women.

METHODS

A soy challenge was used to assess equol-producer status prior to the start of the study in healthy postmenopausal Japanese women. The study involved 4 separate groups in randomised crossover design. First, subjects were classified as equol producers (n = 25) or non-producers (n = 18), and then they were randomly assigned to the FOS or control group. All subjects received a daily dose of 37 mg isoflavone conjugates in the capsule (21 mg aglycone form) and either FOS (5 g/day) or sucrose as control, in a randomised crossover study design. Equol -production was assessed by testing the serum and urine before and after the 2-week supplementation period.

RESULTS

The analyses were conducted on 34 subjects completed the study, 21 (61.8%) were classified as equol producers, and 13 (38.2%) as non-producers. Significant differences were observed in the interaction effect of time × equol state after 1 week of intervention (p = 0.006). However there were no effects after 2 weeks of intervention (p = 0.516). Finally, in both equol producers and non-producers, FOS supplementation did not affect the serum equol concentration or the urinary equol to daidzein concentration ratios.

CONCLUSIONS

We have reported that FOS intervention (5 g/day for 2 weeks) does not significantly modulate the capacity of intestinal microbiota to produce equol in postmenopausal Japanese women, in either equol producers or non-producers in this pilot study. Further larger investigations that explore the roles of specific intestinal microbiota in equol production will enable the establishment of dietary conditions that are required to enhance equol production.

Nutritional flavonoids impact on nuclear and extranuclear estrogen receptor activities

Flavonoids are a large group of nonnutrient compounds naturally produced from plants as part of their defence mechanisms against stresses of different origins. They emerged from being considered an agricultural oddity only after it was observed that these compounds possess a potential protective function against several human degenerative diseases. This has led to recommending the consumption of food containing high concentrations of flavonoids, which at present, especially as soy isoflavones, are even available as overthecounter nutraceuticals. The increased use of flavonoids has occurred even though their mechanisms are not completely understood, in particular those involving the flavonoid impact on estrogen signals. In fact, most of the human health protective effects of flavonoids are described either as estrogenmimetic, or as antiestrogenic, while others do not involve estrogen signaling at all. Thus, the same molecule is reported as an endocrine disruptor, an estrogen mimetic or as an antioxidant without estrogenic effects. This is due in part to the complexity of the estrogen mechanism, which is conducted by different pathways and involves two different receptor isoforms. These pathways can be modulated by flavonoids and should be considered for a reliable evaluation of flavonoid, both estrogenicity and antiestrogenicity, and for a correct prediction of their effects on human health.

Impact of food matrix on isoflavone metabolism and cardiovascular biomarkers in adults with hypercholesterolemia

The role of food matrix and gender on soy isoflavone metabolism and biomarkers of activity were examined in twenty free-living adults (34.7 ± 11.5 years old) with hypercholesterolemia (221.9 ± 18.7mg dL(-1)). In a randomized crossover design study, participants consumed soy bread (3 wk) or a soy beverage (3 wk) containing 20 g soy protein with 99 and 93 mg isoflavones aglycone equivalents per day, respectively. During soy bread intervention, women had significantly greater microbial metabolite excretion (P = 0.05) of isoflavonoids than men. In men, isoflavone metabolite excretion was not discernibly different between the two matrices. Significant reductions (P≤ 0.05) in triglycerides (24.8%), LDL cholesterol (6.0%), apolipoprotein A-I (12.3%), and lipid oxidative stress capacity (25.5%), were observed after soy food intervention. Our findings suggest that the food matrix significantly impacts soy isoflavone metabolism, particularly microbial metabolites in women.

Equol production changes over time in pre-menopausal women

Equol (EQ) is a metabolite produced by gut bacteria through the chemical reduction of the soya isoflavone daidzein (DE), but only by 30-60% of the population. EQ is believed to provide benefits derived from soya intake and its production is widely viewed as a relatively stable phenomenon. In a randomised, cross-over intervention with soya foods, seventy-nine pre-menopausal women were challenged with a high-soya and a low-soya diet each for 6 months, separated by a 1-month washout period. Overnight urine was collected at three time points during each diet period and analysed for DE and EQ by liquid chromatography tandem MS. Remaining an EQ producer (EP) or non-producer (NP) or changing towards an EP or NP was assessed using an EQ:DE ratio of ≥0·018 combined with a DE threshold of ≥2 nmol/mg creatinine as a cut-off point. We observed 19 and 24% EP during the low-soya and high-soya diet periods, respectively, and found that 6-11% of our subjects changed EQ status 'within' each study period (on an average of 1·2 times), while 16% changed 'between' the two diet periods. The present finding challenges the widely held conviction that EQ production within an individual remains stable over time. The precise factors contributing to changes in EQ status, however, remain elusive and warrant further investigation.

GC-MS determined distribution of urinary equol producers as affected by age, gender, and repeated ingestions of soymilk

Status of equol excretion is likely a reflection of incidence risk of sex-hormone related diseases and deserves research attention. In this study, urine samples collected from 182 volunteers after soymilk ingestion were subjected to equol quantification using GC-MS. As categorized into male, female, and both genders and each category further classified into 6 age (year) categories, namely, <20, 21 to 30, 31 to 40, 41 to 50, >51 and overall, a trend indicating that the younger age the higher equol producer ratio was observed. For the >51 subjects, the corresponding producer ratios of males and females were 35.3% and 50.0%, respectively. Among the volunteers, 20 nonproducers were further recruited to ingest 1000 mL soymilk weekly for 16 wk and urines were analyzed bi-weekly. As resulted, 8 of 20 nonproducers were induced to become equol producers. The observed change of nonproducers to equol producers induced by repeating ingestions of soymilk is of merit from the viewpoint of healthcare.

Whole versus the piecemeal approach to evaluating soy

Soy has been singled out for attention among other legumes as a valuable source of nutrients, phytochemicals, and bioactive compounds. Early epidemiological studies established that whole soy and traditional soy foods were implicated in health-protective effects in Asian populations. The same benefits attributable to soy have not been consistently proven in Western populations that, for various reasons, opt to consume more processed soy foods or various soy components. Soy researchers continue to isolate soy components in search of identifying its salubrious components and whole soy remains relatively underinvestigated despite what we know of the health benefits it may confer to those regularly consuming it. Various dietary guidelines advocate the regular consumption of legumes that tend not to be included in our diets in sufficient quantities. This paper highlights the possibility that whole soy may have a more unique effect on health than a select soy component(s). It explores the rationale for focusing research on whole soy in an attempt to understand it better rather than trying to replicate the health benefits by targeting various soy components, which has been plagued by inconsistent results.

Consumption of Lactobacillus acidophilus and Bifidobacterium longum does not alter phytoestrogen metabolism and plasma hormones in men: a pilot study

OBJECTIVE

The aim of this study was to determine whether equol excretion status and plasma hormone and leptin concentrations can be influenced by consumption of a probiotic supplement. A secondary focus was to investigate whether male equol excretors have a hormone profile consistent with reduced prostate cancer risk.

DESIGN

The design was a randomized, single-blinded, placebo-controlled, parallel-arm trial.

SUBJECTS

Thirty-one (31) of the initially enrolled 39 subjects, 18 to 37 years old, completed all study requirements.

INTERVENTION

Subjects consumed either probiotic capsules (containing Lactobacillus acidophilus and Bifidobacterium longum) or placebo capsules for 2 months. Fasting plasma concentrations of testosterone (T), dihydrotestosterone (DHT), androstanediol glucuronide (AAG), androstenedione (A), dehydroepiandrosterone sulfate (DHEAS), sex hormone-binding globulin (SHBG), and leptin were measured on days 1 and 57. Urinary excretion of genistein, glycitein, daidzein, O-desmethylangolensin (O-Dma), and equol was measured on days 4 and 61 following a 4-day soy challenge.

RESULTS

Probiotic consumption did not significantly alter equol excretor status, plasma hormone, or leptin concentrations in these subjects. At baseline, there were no differences in plasma hormone concentrations between equol excretors and nonexcretors; however, the low number of equol excretors included in this study limits the strength of this finding.

CONCLUSIONS

The 2-month intervention with probiotic capsules did not significantly alter equol excretion, plasma hormone, or leptin concentrations in these subjects. A secondary finding was that male equol excretors in this study did not exhibit a hormone profile consistent with reduced prostate cancer risk, although this result should be interpreted with caution.

Bioavailability of isoflavone phytoestrogens in postmenopausal women consuming soya milk fermented with probiotic bifidobacteria

We investigated the effects of consuming an isoflavone aglycone-enriched soya milk containing viable bifidobacteria on urinary isoflavone excretion and percentage recovery. Sixteen postmenopausal women were randomly divided into two groups to consume either fermented or non-fermented soya milk. Each group participated in a double-blind, crossover study with three 14 d supplementation periods, separated by a 14 d washout. Subjects ingested three daily dosages of isoflavone via the soya milk and collected four 24 h pooled urine specimens per supplementation period. Soya milks were prepared with soya protein isolate and soya germ, followed by fermentation with bifidobacteria. Isoflavone levels were quantified using HPLC. Non-fermented soya milks at 20, 40 and 80 mg isoflavone/200 ml contained 10 %, 9 % and 7 % aglycone, respectively, with their fermented counterparts containing 69 %, 57 % and 36 % aglycone (P<0·001). A trend to a greater percentage urinary recovery of daidzein and glycitein was observed among women consuming fermented soya milk at a dosage of 40 mg isoflavone (P=0·13). A distinct linear dose response for the fermented soya milk group (R2=0·9993) compared with the non-fermented group (R2=0·8865) suggested less interindividual variation in isoflavone absorption. However, total urinary isoflavone excretion was similar for both groups (P>0·05), with urinary isoflavone recovery at approximately 31 %. Increasing the isoflavone dosage correlated positively with its urinary excretion, but urinary percentage recovery of isoflavone was inversely related to dosage level. Hence, a modest dosage ranging from 20 to 30 mg/d may provide the most bioavailable source of isoflavone, regardless of whether it is via an aglycone-rich fermented soya milk or a glucoside-rich soya milk.

One-month exposure to soy isoflavones did not induce the ability to produce equol in postmenopausal women

OBJECTIVE

As more and more postmenopausal women are taking soy isoflavone supplementation for relieving menopausal symptoms, we investigated the impact of chronic exposure on their bioavailability, with focus on achievable plasma concentrations and potential stimulation of the capacity to produce equol.

SUBJECTS

A total of 12 Caucasian postmenopausal women.

INTERVENTION

Volunteers ingested 100 mg isoflavones/day (aglycone equivalents, in cereal bars and yoghurts) for 1 month. Plasma concentrations of metabolites at 2, 4, 6, 8, 10, 12 and 24 h postdose, as well as urinary excretion in fractions over 36 h were compared between days 1 and 30.

RESULTS

Similar plasma kinetic curves were obtained at day 1 and day 30 for genistein and daidzein. Maximum plasma concentrations were 1.68+/-0.68 micromol/l on day 1 compared to 2.27+/-0.76 micromol/l on day 30 for daidzein (P=0.056), and 3.88+/-1.50 micromol/l on day 1 compared to 5.30+/-2.38 micromol/l on day 30 for genistein (P=0.091). Urinary excretion of daidzein and genistein did not differ significantly between days 1 and 30. Maximum plasma concentration of equol increased significantly from 0.31+/-0.27 to 0.99+/-0.51 micromol/l for equol-producer volunteers (P=0.046). However, the seven volunteers who were classified as non-equol producers on day 1 did not acquire the ability to produce equol after 1-month exposure.

CONCLUSIONS

Chronic exposure to isoflavones in postmenopausal women resulted in plasma concentrations as high as 2.5-5 micromol/l of each isoflavone, but did not induce the ability to produce equol.

Concentrations of isoflavones in plasma and urine of post-menopausal women chronically ingesting high quantities of soy isoflavones

Soy food or food supplements based on soy containing isoflavones (Isos) are increasingly available in Western countries. However, the variability of Isos levels in urine and plasma in humans during chronic ingestion is poorly documented. Nevertheless, this is the way these compounds will most probably be used in the future, especially if the soy-based supplements market goes on increasing. Here, glycosilated Isos in an enriched extract of Prevastein equal to 100 mg of equivalent Isos aglycone was given daily to 27 post-menopausal women for 30 days and to 12 post-menopausal women for 60 days. Volunteers were given Prevastein in a cereal bar (25 mg Isos) and in a yoghurt (25 mg Isos) both at breakfast and dinner. Plasma samples were collected after overnight fasting. Urine samples were aliquots of a 24 h collection checked on volume and creatinin excretion levels. Genistein, daidzein and equol were measured at day 0 and every 15 days afterwards, using original specific ELISAs. Constant levels were reached from the 15th day. About 59.2% of the volunteers were significant equol producers in the first experiment and 58.3% in the second. A large variability in plasma and urine levels was observed among post-menopausal women consuming 100 mg Isos per day, although remaining relatively stable in each individual subject. This could partly account for the controversial effects of Isos recorded so far in clinical studies. So Isos plasma levels would have to be assayed during chronic exposures, and could help to better understand the large variability of the effects classically observed in clinical studies. ELISA techniques could be easily exported to analytical laboratories to help physicians and nutritionists with their prescriptions.

Genistein stimulates growth of human breast cancer cells in a novel, postmenopausal animal model, with low plasma estradiol concentrations

We have demonstrated that genistein (GEN) stimulates growth of estrogen-dependent breast tumors in vivo. In this study, we evaluated whether dietary GEN can act in an additive manner with low circulating levels of 17beta-estradiol (E2). We developed an E2 delivery system using silastic implants that yield low circulating plasma E2 levels similar to those observed in postmenopausal women. We inserted various concentrations of E2 silastic implants (1:127, 1:63, 1:31, 1:15 and 1:7 = E2:cholesterol) and injected estrogen-dependent human breast cancer (MCF-7) cells into ovariectomized athymic mice. The E2 implants tested (1:127-1:7) generated 30.1-101.6 pM E2 in plasma, which is comparable to the E2 levels observed in postmenopausal women. The E2 implants stimulated MCF-7 tumor growth in a dose-dependent manner. We selected the 1:31 ratio of E2 implant to evaluate if dietary GEN acts in an additive manner with low E2 levels to influence the growth of MCF-7 tumors. Ovariectomized mice were divided into four groups: MCF-7 control, 500 ppm GEN, 1:31 E2, and 1:31 E2 + 500 ppm GEN. At week 17, the average tumor sizes were 7.6, 32.1, 67.4 and 106.8 mm2 for these groups, respectively (P < 0.05), demonstrating that 500 ppm GEN additively stimulated MCF-7 tumor growth in the presence of low levels of E2. In summary, we established a preclinical mouse model that results in E2 blood concentrations similar to those found in postmenopausal women. Further, we observed that these concentrations regulate the growth rate of MCF-7 breast tumors. Using this model, we demonstrated that dietary GEN in the presence of low levels of circulating E2 act in an additive manner to stimulate estrogen-dependent tumor growth in vivo. Results from this study suggest that consumption of products containing GEN may not be safe for postmenopausal women with estrogen-dependent breast cancer.

Soy phytochemicals prevent orthotopic growth and metastasis of bladder cancer in mice by alterations of cancer cell proliferation and apoptosis and tumor angiogenesis

A role of dietary bioactive components in bladder cancer prevention is biologically plausible because most substances or metabolites are excreted through the urinary tract and are consequently in direct contact with the mucosa of the bladder. We first determined antigrowth activity of genistein against poorly differentiated 253J B-V human bladder cancer cells in vitro. Genistein inhibited the cell growth in a time- and dose-dependent manner via G(2)-M arrest, down-regulation of nuclear factor kappaB (NF-kappaB), and induction of apoptosis. We also evaluated both genistin, which is a natural form of genistein, and the isoflavone-rich soy phytochemical concentrate (SPC) on the growth and metastasis of 253J B-V tumors in an orthotopic tumor model. Mice treated with genistin and SPC had reduced final tumor weights by 56% (P < 0.05) and 52% (P < 0.05), respectively, associated with induction of tumor cell apoptosis and inhibition of tumor angiogenesis in vivo. In addition, SPC treatment, but not genistin treatment, significantly inhibited lung metastases by 95% (P < 0.01) associated with significant down-regulation of NF-kappaB expression in tumor tissues and reduction of circulating insulin-like growth factor-I levels, suggesting that SPC may contain other bioactive ingredients that have antimetastatic activity. The results from our studies suggest that further clinical investigation should be warranted to apply soy phytochemicals, such as SPC, as a potent prevention regimen for bladder cancer progression. This orthotopic human bladder tumor model also provides a clinically relevant experimental tool for assessing potential preventive activity of other dietary components against bladder tumor growth and metastasis.

Effects of dietary daidzein and its metabolite, equol, at physiological concentrations on the growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in ovariectomized athymic mice

Genistein and daidzein are the main isoflavones in legumes. Equol is an intestinal bacterial metabolite of daidzein. In this study, we evaluated the estrogenic potential of daidzein and synthetic (+/-)-equol to stimulate growth of estrogen-dependent breast cancer (MCF-7) in vitro and in vivo. We hypothesize that estrogenic effects of daidzein and (+/-)-equol could modulate the growth of MCF-7 cells both in vitro and also once implanted into ovariectomized athymic mice. At concentrations between 0.001 and 50 microM, daidzein and (+/-)-equol stimulated the growth of MCF-7 cells with maximal stimulation at 1 muM in vitro. To evaluate their effects on the growth of MCF-7 cells implanted in ovariectomized athymic mice, two dietary dose-response studies [daidzein (125, 250, 500 and 1000 p.p.m.) and (+/-)-equol (250, 500 and 1000 p.p.m.)] were conducted. Tumor size and body weight were monitored weekly during the study. At completion of the study, we analyzed cellular proliferation of tumors using immunohistochemical staining (ki-67), pS2 expression in tumors using a real time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and total daidzein and (+/-)-equol levels in plasma using liquid chromatography-electrospray tandem mass spectrometry (LC-ES/MS/MS). Dietary daidzein had a slight but significant stimulatory effect on MCF-7 tumor growth in mice. No significant induction of pS2 mRNA (an estrogen-responsive marker) in tumors by dietary daidzein was observed. Total plasma daidzein concentrations in plasma were between 0.25 and 1.52 microM. Dietary equol treatment (for 37 weeks) did not stimulate MCF-7 tumor growth. There were no statistical differences in tumor size, proliferation and pS2 expression among any treatment groups. Total equol concentrations in plasma were 2.10-3.21 microM. In conclusion, daidzein and (+/-)-equol have proliferative effects on MCF-7 cell growth in vitro within the concentration range tested. Dietary daidzein had a slight but significant stimulatory effect on tumor growth, whereas (+/-)-equol did not stimulate the growth of estrogen-dependent breast tumor growth in athymic mice, increase the cell proliferation in tumors, or induce an estrogen-responsive pS2 expression. Total daidzein or (+/-)-equol plasma levels in mice fed the isoflavones were in the range that stimulated MCF-7 cell growth in vitro. These results suggest that pharmacokinetic and/or metabolic factors attenuate the estrogenic effects of daidzein and equol in vivo.

Urinary isoflavone excretion as a compliance measure in a soy intervention among young girls: a pilot study

OBJECTIVE

To investigate the compliance of young girls with a soy intervention.

DESIGN

An 8-week dietary intervention and urine sample collection.

SETTING

Free-living girls.

SUBJECTS

A convenience sample of 8- to 14-y-old girls (20 started and 17 finished the study) recruited through flyers distributed to staff members and previous study participants.

INTERVENTION

The girls consumed one daily serving of soymilk, soy nuts, or tofu, completed 3-day food records, kept daily soy intake logs, and collected weekly urine samples.

MAIN OUTCOME MEASURES

Compliance with the intervention was evaluated by daily soy intake logs, 3-day food records analyzed by the center's Food Composition and Food Groups Servings Databases, and weekly urinary isoflavone excretion using high-pressure liquid chromatography. The statistical analysis included paired t-tests, analysis of variance, and Spearman's rank-order correlation coefficients.

RESULTS

Daily soy intake logs indicated a mean intake of 6.28 servings out of a maximum of 7.0 servings per week. The food records revealed a six-fold increase in isoflavone intake during the study period (P<0.01) which was confirmed by an increase in urinary isoflavone excretion of similar magnitude (23.3-142.1 nmol/mg creatinine, P=0.02).

CONCLUSIONS

This study demonstrated the ability of young girls to consume one daily soy serving and the usefulness of urinary isoflavones as a primary compliance measure. The high urinary isoflavone excretion levels detected in girls as compared to adult women suggest less intestinal degradation and/or greater absorption of isoflavones in nonadult populations. This finding requires further investigations into the pharmacokinetics of isoflavones.

Consumption of Lactobacillus acidophilus and Bifidobacterium longum do not alter urinary equol excretion and plasma reproductive hormones in premenopausal women

OBJECTIVE

To confirm the results of an earlier study showing premenopausal equol excretors to have hormone profiles associated with reduced breast cancer risk, and to investigate whether equol excretion status and plasma hormone concentrations can be influenced by consumption of probiotics.

DESIGN

A randomized, single-blinded, placebo-controlled, parallel-arm trial.

SUBJECTS

In all, 34 of the initially enrolled 37 subjects completed all requirements.

INTERVENTION

All subjects were followed for two full menstrual cycles and the first seven days of a third cycle. During menstrual cycle 1, plasma concentrations of estradiol (E(2)), estrone (E(1)), estrone-sulfate (E(1)-S), testosterone (T), androstenedione (A), dehydroepiandrosterone-sulfate (DHEA-S), and sex-hormone-binding globulin (SHBG) were measured on cycle day 2, 3, or 4, and urinary equol measured on day 7 after a 4-day soy challenge. Subjects then received either probiotic capsules (containing Lactobacillus acidophilus and Bifidobacterium longum) or placebo capsules through day 7 of menstrual cycle 3, at which time both the plasma hormone concentrations and the post-soy challenge urinary equol measurements were repeated.

RESULTS

During menstrual cycle 1, equol excretors and non-excretors were not significantly different with respect to subject characteristics, diet, or hormone concentrations. Significant inverse correlations were found between E(2) and body mass index (BMI) (P=0.02), SHBG and BMI (P=0.01), DHEA-S and dietary fiber (P=0.04), and A and protein:carbohydrate ratio (P=0.02). Probiotic consumption failed to significantly alter equol excretor status or hormone concentrations during menstrual cycle 3, although there were trends towards decreased concentrations of T (P=0.14) and SHBG (P=0.10) in the probiotic group.

CONCLUSIONS

We were unable to verify a previously reported finding of premenopausal equol excretors having plasma hormone concentrations different from those of nonexcretors. Furthermore, a 2-month intervention with probiotic capsules did not significantly alter equol excretion or plasma hormone concentrations.

Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies

Polyphenols are abundant micronutrients in our diet, and evidence for their role in the prevention of degenerative diseases is emerging. Bioavailability differs greatly from one polyphenol to another, so that the most abundant polyphenols in our diet are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Mean values for the maximal plasma concentration, the time to reach the maximal plasma concentration, the area under the plasma concentration-time curve, the elimination half-life, and the relative urinary excretion were calculated for 18 major polyphenols. We used data from 97 studies that investigated the kinetics and extent of polyphenol absorption among adults, after ingestion of a single dose of polyphenol provided as pure compound, plant extract, or whole food/beverage. The metabolites present in blood, resulting from digestive and hepatic activity, usually differ from the native compounds. The nature of the known metabolites is described when data are available. The plasma concentrations of total metabolites ranged from 0 to 4 mumol/L with an intake of 50 mg aglycone equivalents, and the relative urinary excretion ranged from 0.3% to 43% of the ingested dose, depending on the polyphenol. Gallic acid and isoflavones are the most well-absorbed polyphenols, followed by catechins, flavanones, and quercetin glucosides, but with different kinetics. The least well-absorbed polyphenols are the proanthocyanidins, the galloylated tea catechins, and the anthocyanins. Data are still too limited for assessment of hydroxycinnamic acids and other polyphenols. These data may be useful for the design and interpretation of intervention studies investigating the health effects of polyphenols.

Urinary isoflavonoid excretion is inversely associated with the ratio of protein to dietary fibre intake in young women

OBJECTIVE

To examine the prevalence of excretion of urinary isoflavonoids in women and determine any relationships with accustomed macronutrient intake.

DESIGN

Volunteers in one of two 4-month studies. Study 1 was a randomised crossover study whereby subjects consumed a placebo or isoflavone supplement for 2 months and crossed over. Study 2 was a parallel design in which subjects consumed a placebo for 1 month and an isoflavone supplement for 3 months.

SETTING

All subjects were free-living, healthy volunteers.

SUBJECTS

A total of 25 (study 1, n=14; study 2, n=11) premenopausal women were recruited through advertisements.

INTERVENTIONS

Volunteers were supplemented for 2 months (study 1) or 3 months (study 2) with purified isoflavones (86 mg/day) derived from red clover. Urinary isoflavonoids were measured during the placebo and the second month of isoflavone treatment. Macronutrient intakes were determined from weighed food records.

RESULTS

During isoflavone supplementation, the concentration of urinary total isoflavonoids increased by 15-fold (P<0.0001), with 5.4-fold variation between individuals. Multiple linear regression analysis showed that 24% of this variation could be explained by an interaction between dietary fibre and protein (P=0.047), with a highly significant inverse association between total isoflavonoid concentration and the protein to fibre ratio (r=-0.51, P=0.009).

CONCLUSIONS

Supplementation with purified isoflavones results in an increase in urinary isoflavonoid excretion and part of the individual variation in response is associated with an interaction between intakes of protein and dietary fibre. Whether manipulation of these macronutrients could enhance efficacy of isoflavone supplements remains to be determined.

Influence of 10 wk of soy consumption on plasma concentrations and excretion of isoflavonoids and on gut microflora metabolism in healthy adults

BACKGROUND

Little information is currently available on the role of the gut microflora in modulating isoflavone bioavailability or on sex differences in isoflavone metabolism and bioavailability.

OBJECTIVE

We sought to determine whether chronic soy consumption influences isoflavone bioavailability as judged by plasma isoflavone concentrations and modified gut microflora activities [beta-glucoside hydrolysis and equol and O-desmethylangolensin (O-DMA) production]. We also examined whether sex differences in isoflavone metabolism exist.

DESIGN

A randomized, parallel, controlled study design was used to compare a high-soy diet (104 +/- 24 mg total isoflavones/d) with a low-soy diet (0.54 +/- 0.58 mg total isoflavones/d) in 76 healthy young adults for 10 wk.

RESULTS

Concentrations of isoflavones and their gut microflora metabolites in the plasma, urine, and feces were significantly higher in the subjects who consumed the high-soy diet than in those who consumed the low-soy diet. Concentrations of O-DMA in plasma and urine were higher in the men than in the women. Fecal bacteria from subjects consuming both diets could convert daidzein to equol ex vivo. Fecal beta-glucosidase activity was significantly higher in the subjects who consumed the high-soy diet than in those who consumed the low-soy diet.

CONCLUSIONS

Although interindividual variation in isoflavone metabolism was high, intraindividual variation was low. Only concentrations of O-DMA in plasma and urine appeared to be influenced by sex. Chronic soy consumption does not appear to induce many significant changes to the gut metabolism of isoflavones other than higher beta-glucosidase activity.

Polyphenols: food sources and bioavailability

Polyphenols are abundant micronutrients in our diet, and evidence for their role in the prevention of degenerative diseases such as cancer and cardiovascular diseases is emerging. The health effects of polyphenols depend on the amount consumed and on their bioavailability. In this article, the nature and contents of the various polyphenols present in food sources and the influence of agricultural practices and industrial processes are reviewed. Estimates of dietary intakes are given for each class of polyphenols. The bioavailability of polyphenols is also reviewed, with particular focus on intestinal absorption and the influence of chemical structure (eg, glycosylation, esterification, and polymerization), food matrix, and excretion back into the intestinal lumen. Information on the role of microflora in the catabolism of polyphenols and the production of some active metabolites is presented. Mechanisms of intestinal and hepatic conjugation (methylation, glucuronidation, sulfation), plasma transport, and elimination in bile and urine are also described. Pharmacokinetic data for the various polyphenols are compared. Studies on the identification of circulating metabolites, cellular uptake, intracellular metabolism with possible deconjugation, biological properties of the conjugated metabolites, and specific accumulation in some target tissues are discussed. Finally, bioavailability appears to differ greatly between the various polyphenols, and the most abundant polyphenols in our diet are not necessarily those that have the best bioavailability profile. A thorough knowledge of the bioavailability of the hundreds of dietary polyphenols will help us to identify those that are most likely to exert protective health effects.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

Dietary constituents as novel therapies for pain

The use of complementary and alternative medicine has dramatically increased in the United States. The effects of select dietary constituents in animal models and clinical pain states are reviewed. Specifically, the antinociceptive and analgesic properties of soybeans, sucrose, and tart cherries are discussed. The potential actions of dietary constituents as antiinflammatory and antioxidant agents are presented.

Bioavailability of phyto-oestrogens

The term phyto-oestrogen encompasses isoflavone compounds, such as genistein and daidzein, found predominantly in soya products and the lignans, such as matairesinol and secoisolariciresinol, found in many fruits, cereals and in flaxseed. There is evidence that they have potential health benefits in man particularly against hormone-dependent diseases such as breast and prostate cancers and osteoporosis. This has led to intense interest in their absorption and biotransformation in man. The metabolism of isoflavones and lignans in animals and man is complex and involves both mammalian and gut microbial processes. Isoflavones are present predominantly as glucosides in most commercially available soya products; there is evidence that they are not absorbed in this form and that their bioavailability requires initial hydrolysis of the sugar moiety by intestinal beta-glucosidases. After absorption, phyto-oestrogens are reconjugated predominantly to glucuronic acid and to a lesser degree to sulphuric acid. Only a small portion of the free aglycone has been detected in blood, demonstrating that the rate of conjugation is high. There is extensive further metabolism of isoflavones (to equol and O-desmethylangolensin) and lignans (to enterodiol and enterolactone) by gut bacteria. In human subjects, even those on controlled diets, there is large interindividual variation in the metabolism of isoflavones and lignans, particularly in the production of the gut bacterial metabolite equol (from daidzein). Factors influencing absorption and metabolism of phyto-oestrogens include diet and gut microflora.

Analysis of phyto-oestrogens in biological matrices

A review covering different methods for the analysis of phyto-oestrogens in biological matrices is presented. Sample pretreatment and analysis of isoflavonoids and lignans by HPLC and GC with various detection methods are discussed. The immunoassay method is also briefly presented.

Isoflavonoid and lignan phytoestrogens as dietary biomarkers

Isoflavones and lignans are biologically active plant-food constituents that have potential chemopreventive properties. Quantitation of isoflavones and lignans in humans is necessary to establish the benefits and risks of exposure to these compounds in populations and to determine which components of a mixed diet contribute to the exposure. Isoflavones and lignans are metabolized by colonic bacteria to more biologically active metabolites; thus both the parent compounds and the metabolites are measured routinely. Isoflavonoids (genistein, daidzein, dihydrodaidzein, O-desmethylangolensin and equol) and lignans (enterolactone, enterodiol, matairesinol and secoisolariciresinol) can be quantified in various body fluids. Typically, high concentrations of isoflavonoids in urine and serum are associated with soy consumption, and high concentrations of lignans are associated primarily with intake of whole grains and other fiber-containing plant foods. Controlled feeding studies and nutritional epidemiologic studies demonstrate a linear dose response between dietary intake and urinary excretion of isoflavones. Lignan excretion is associated positively with dietary fiber intake as well as with diets that are on average higher in fiber and carbohydrate and lower in fat; thus lignans have also been proposed as a marker of healthier dietary patterns. The complex interactions between the colonic environment and the external and internal factors that modulate it contribute to significant variation in serum and urinary phytoestrogen levels among individuals. Understanding these sources of variation is important to be able to use these measures effectively as dietary biomarkers.

Comparing the pharmacokinetics of daidzein and genistein with the use of 13C-labeled tracers in premenopausal women

BACKGROUND

Despite significant interest in the risks and benefits of phytoestrogens to human health, few data exist on their pharmacokinetics in humans.

OBJECTIVE

We investigated the pharmacokinetics of the (13)C isotopic forms of daidzein and genistein in healthy humans, specifically addressing intraindividual variability, effect of increasing intake, and influence of prolonged exposure to a soy food diet.

DESIGN

Premenopausal women (n = 16) were administered 0.4 mg [(13)C]daidzein or [(13)C]genistein/kg body wt orally on 3 occasions, including once after eating soy foods for 7 d. On a further occasion the dose was doubled. Plasma and urinary [(13)C]isoflavone concentrations were measured by mass spectrometry.

RESULTS

Serum concentrations of [(13)C]genistein and [(13)C]daidzein peaked after 5.5 and 7.4 h, respectively. The systemic bioavailability and maximum serum concentration of [(13)C]genistein were significantly greater than those of [(13)C]daidzein. The bioavailability of both isoflavones did not increase linearly when the dietary intake was doubled. The mean volume of distribution normalized to bioavailability (V(d)/F), clearance rate, and half-life of [(13)C]daidzein were 336.25 L, 30.09 L/h, and 7.75 h, respectively; the corresponding values for [(13)C]genistein were 258.76 L, 21.85 L/h, and 7.77 h. The average recovery of [(13)C]daidzein and [(13)C]genistein in urine was 30.1% and 9.0% of the dose ingested, respectively.

CONCLUSIONS

The serum pharmacokinetics of [(13)C]daidzein and [(13)C]genistein were reproducible among healthy women, and genistein was more bioavailable than was daidzein. Pharmacokinetics were unaffected by chronic exposure to soy foods. Urinary isoflavone concentrations correlated poorly with maximal serum concentrations, indicating the limitations of urine measurements as a predictor of systemic bioavailability. The bioavailability of both isoflavones was nonlinear at higher intakes, suggesting that uptake is rate-limiting and saturable.

Phytoestrogens as modulators of steroid action in target cells

Although numerous reports exist on the potential beneficial role of nutritional phytoestrogens in human health, their molecular mechanism in target cells is still not completely understood. Phytoestrogens promote estrogen and antiestrogen effects by interacting with numerous molecules, carrier proteins, enzymes and membrane and nuclear receptors, directly or indirectly involved in the transfer of estrogen signals. The hypothesis that the ER beta subtype plays a key role in antiproliferative effect of phytoestrogens, especially in breast cancer, is examined here. This review focus on the effects of phytoestrogens in developmental processes such as those linked to reproductive function, tumorigenesis and angiogenesis.

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.

Isoflavones for prevention of cancer, cardiovascular diseases, gynecological problems and possible immune potentiation

Japanese women show low incidence of and mortality from breast cancer, cardiovascular disease and climacteric symptoms compared to Caucasians. High soy bean intake is considered to attribute to that, but it is not clear whether soy protein itself or isoflavones (IFs) mixed in the soy protein has such effects. Presence of IFs in soy beans was varied by site, so we made IF-rich tablets from daidzein-rich soy germ (hypocotyl) for intervention studies. Our intervention study on young women by using the IF-rich tablet (20 and 40 mg/day) showed slight elongation of the menstrual cycle, but no adverse effects occurred. Intervention study on climacteric women showed improvement of bone density, hypertension and climacteric symptoms. Health effects of IFs on cancer occurrence, cardiovascular diseases, gynecological problems and possible immune potentiation are reviewed from functional aspects.

The specific role of isoflavones on estrogen metabolism in premenopausal women

BACKGROUND

There is increasing evidence that dietary factors may play a role in the production, metabolism, and bioavailability of sex hormones and their impact on target tissues. The specific objective of this study was to evaluate the effectiveness of supplementing a group of premenopausal women who were free of breast carcinoma with a dietary supplement of isoflavones (40 mg per day) in producing a change in steroid hormones and menstrual cycle length.

METHODS

Sixty-eight consecutively recruited, premenopausal, omnivorous women of all races and ethnicities between the ages of 25 years and 55 years were admitted to the study and randomized to an experimental group supplemented with soy (40 mg genistein per day) or to a control group that consumed a placebo for a 12-week period. Changes in their anthropometric, nutritional, and hormonal biomarkers from early follicular phase were analyzed at baseline and post-intervention.

RESULTS

Serum-free estradiol and estrone levels decreased moderately in the experimental group. Serum hormone-binding globulin levels increased in 41.4% of women in the experimental group compared with 37.5% of women in the placebo group. Free estradiol decreased in 53.85% of women in the experimental group compared with 37.5% of women in the placebo group. Estrone decreased in 55.56% of women in the experimental group compared with 42.86% in the placebo group. Those women in the experimental group who were consuming soy had their mean menstrual cycle length increased by 3.52 days compared with a mean decrease of 0.06 days for women in the placebo group (P = 0.04) from baseline to the third menstrual cycle. In addition, women who were taking soy had their mean follicular phase increase by 1.46 days compared with a mean increase of 0.14 days for women who were taking the placebo (P = 0.08).

CONCLUSIONS

These data suggest that increased isoflavone intake affects estrogen metabolism by altering the steroid hormone concentrations and menstrual cycle length, thereby demonstrating a potential to reduce the risk for breast carcinoma.

Effect of soy protein on endogenous hormones in postmenopausal women

BACKGROUND

The long-term clinical effects of soy protein containing various concentrations of isoflavones on endogenous hormones are unknown.

OBJECTIVE

We examined the effects of ingestion of soy protein containing various concentrations of isoflavones on hormone values in postmenopausal women.

DESIGN

Seventy-three hypercholesterolemic, free-living, postmenopausal women participated in a 6-mo double-blind trial in which 40 g protein as part of a National Cholesterol Education Program Step I diet was provided as casein from nonfat dry milk (control), isolated soy protein (ISP) containing 56 mg isoflavones (ISP56), or ISP containing 90 mg isoflavones (ISP90). Endogenous hormone concentrations were measured at baseline and at 3 and 6 mo.

RESULTS

The concentration of thyroxine and the free thyroxine index were higher in the ISP56 group, and the concentration of thyroid-stimulating hormone was higher in the ISP90 group than in the control group at 3 and 6 mo (P < 0.05). Triiodothyronine was significantly higher in the ISP90 group only at 6 mo. Thyroxine, free thyroxine index, and thyroid-stimulating hormone at 6 mo were inversely associated with measures of baseline estrogenicity. No significant differences were found for endogenous estrogens, cortisol, dehydroepiandrosterone sulfate, insulin, glucagon, or follicle-stimulating hormone after baseline hormone values were controlled for.

CONCLUSIONS

This study does not provide evidence that long-term ingestion of soy protein alters steroid hormone values, but it suggests that soy protein may have small effects on thyroid hormone values that are unlikely to be clinically important. The thyroid effects are, however, consistent with previous findings in animals and highlight the need for future research investigating possible mechanisms of action.

Assessing the accuracy of a food frequency questionnaire for estimating usual intake of phytoestrogens

The primary objective of this study was to assess the accuracy of a modified Block food frequency questionnaire (FFQ) with respect to its ability to assess usual dietary intakes of daidzein and genistein. Participants were a convenience sample of 51 Japanese and 18 Caucasian women. All interviews were conducted between February 1997 and October 1997. At each of the four study visits, participants provided a 24-hour urine specimen and a 48-hour dietary recall. At the first visit, participants also completed an interviewer-administered modified Block FFQ. The daidzein and genistein intakes estimated using the FFQ were moderately correlated with the mean estimates of daidzein and genistein intake calculated from four 48-hour dietary recalls (correlation for daidzein = 0.49-0.58 and correlation for genistein = 0.45-0.54) and estimates of urinary concentrations of these compounds calculated from four collections (correlations for daidzein and genistein = 0.49 and 0.30, respectively). The accuracy of the modified Block FFQ for assessment of usual daidzein and genistein intakes is supported by this study. These results support the use of this instrument in epidemiological studies as an easy and low-cost method to assess the usual dietary daidzein or genistein intake.

A critical evaluation of the application of biomarkers in epidemiological studies on diet and health

One of the problems which may beset epidemiological studies is the difficulty of accurately measuring the dietary intakes of participants. Biomarkers of diet promise to provide a more accurate measure of dietary intake and a more objective one in that they are not reliant on the subject's memory. This review considers some issues of importance in epidemiology when information is obtained from biomarkers. The approach taken is to use examples both of normal dietary constituents and of contaminants in relation to a range of diet and health questions to illustrate these points. A brief overview of the role of sample collection, processing and storage is given including some generic recommendations for maximising the reliability of subsequent analytical data. Using the examples of phytoestrogens and iodine the question of whether biomarkers can accurately reflect the intake of the dietary constituents of interest at the population level or at the individual level is considered. The relationship of the biomarker to the natural history of the disease is exemplified using the role of folate in neural tube defects. Finally, intakes of vitamin D and heterocyclic amines are used to illustrate the integration of biomarkers into epidemiological studies of prostate and colorectal cancer, respectively. It is concluded that biomarkers may provide a more accurate and objective measure of diet than estimates of current or usual intake but that this approach also has limitations. A combination of methods will probably prove to be most valuable and this approach is being taken in current large prospective studies.

Dietary agents in cancer prevention: flavonoids and isoflavonoids

Flavones and isoflavones may play a prominent role in cancer prevention since these compounds are found in numerous plants that are associated with reduced cancer rates. This article reviews recent epidemiological and animal data on isoflavones and flavones and their role in cancer prevention. It covers aspects of the bioavailability of these dietary constituents and explores their mechanism of action. Human epidemiology data comes primarily from studies in which foods rich in isoflavones or flavones are associated with cancer rates. This approach has been particularly useful with isoflavones because of their abundance in specific foods, including soy foods. The bioavailability of flavones and isoflavones has been shown to be influenced by their chemical form in foods (generally glycoside conjugates), their hydrophobicity, susceptibility to degradation, the microbial flora of the consumer, and the food matrix. Some information is available on how these factors influence isoflavone bioavailability, but the information on flavones is more limited. Many mechanisms of action have been identified for isoflavone/flavone prevention of cancer, including estrogenic/antiestrogenic activity, antiproliferation, induction of cell-cycle arrest and apoptosis, prevention of oxidation, induction of detoxification enzymes, regulation of the host immune system, and changes in cellular signaling. It is expected that some combination of these mechanisms will be found to be responsible for cancer prevention by these compounds. Compelling data suggest that flavones and isoflavones contribute to cancer prevention; however, further investigations will be required to clarify the nature of the impact and interactions between these bioactive constituents and other dietary components.

Wheat bran and soy protein feeding do not alter urinary excretion of the isoflavan equol in premenopausal women

The capacity to convert the soy isoflavone daidzein to equol in vivo is presumably determined by an individual's intestinal microfloral populations; however, diet may also influence this conversion. The objectives of the present study were to determine whether a 1-mo supplementation of dietary fiber as wheat bran increases urinary equol excretion in equol excreters and stimulates equol production in nonexcreters and whether longer-term soy isoflavone intake increases equol production or alters overall urinary isoflavone excretion. First, we screened 74 women, ages 20-40 y, and determined their equol-excreter status. In these women, health and lifestyle patterns and habitual dietary intake did not differ according to equol-excreter status. Next, 26 of the women (13 equol excreters and 13 nonexcreters) were assigned (blocked on equol-excreter status) to either longer-term (1 mo) or short-term (4 d) soy protein supplementation. Within each soy treatment group, women participated in two 1-mo intervention periods (the exact length was determined by each woman's menstrual cycle) during which they consumed their usual diets supplemented daily with either 0 or 16 g dietary fiber in a randomized crossover design. A 1-mo washout period separated the two diet periods. Among the 19 women who completed both periods, fiber supplementation did not increase equol production in equol excreters or nonexcreters. In addition, isoflavonoid excretion did not differ by fiber dose or length of soy intervention. These results suggest that a daily 16 g-fiber dose as wheat bran and the addition of soy protein do not alter significantly the capacity of colonic microflora to produce equol.

Cholesterol lowering benefits of soy and linseed enriched foods

Foods such as breads and breakfast cereals enriched with a combination of soy protein (soy grits and/or soy flour) and whole linseed are gaining popularity. Regular consumption of either whole grains or soy protein can lower risk factors for coronary heart disease. Furthermore, linseed is a rich source of the omega-3 fatty acid. alpha-linolenic acid (LNA), with purported cardiovascular benefits. The aim of this study was to determine the effect of daily consumption of soy and linseed containing foods and Canola (as an added source of LNA) on plasma lipid concentrations in 20 mildly hypercholesterolaemic postmenopausal women. Fasted blood samples were taken initially and after 3 and 8 weeks to assay plasma lipids and both plasma and erythrocyte membrane fatty acids. Urinary isoflavones were also measured. Data from 18 subjects were used for analysis. Plasma total, low-density lipoprotein (LDL) and non-high-density lipoprotein (HDL) cholesterol concentrations fell significantly (10, 12.5 and 12%, respectively) within 3 weeks. Although attenuated, there were still significant reductions in total and non-HDL cholesterol (5 and 6.5%, respectively) after 8 weeks of intervention. These reductions were associated with increases in urinary isoflavone excretion. This pilot study indicates that regular inclusion of foods containing soy and linseed in the diet may improve plasma lipids in subjects with hypercholesterolaemia.

Interindividual variation in metabolism of soy isoflavones and lignans: influence of habitual diet on equol production by the gut microflora

The soy isoflavones, daidzein and genistein, and the lignans, matairesinol and secoisolariciresinol, are phytoestrogens metabolized extensively by the intestinal microflora. Considerable important evidence is already available that shows extensive interindividual variation in isoflavone metabolism, and we have investigated the extent of this variation in a crossover study of a soy-containing food low or high in isoflavones (each treatment period lasted for 17 days, and the 2 treatment periods were separated by a 25-day washout period) in 24 healthy subjects [19 women and 5 men, mean age 30 yr, range 19-40, mean body mass index 22.5 +/- 3.5 (SD) kg/m2]. There was a 16-fold variation in total isoflavonoid excretion in urine after the high-isoflavone treatment period. The variation in urinary equol excretion was greatest (664-fold), and subjects fell into two groups: poor equol excretors and good equol excretors (36%). A significant negative correlation was found between the proportion of energy from fat in the habitual diet and urinary equol excretion (r = -0.55; p = 0.012). Good equol excretors consumed less fat as percentage of energy than poor excretors (26 +/- 2.3% compared with 35 +/- 1.6%, p < 0.01) and more carbohydrate as percentage of energy than poor excretors (55 +/- 2.9% compared with 47 +/- 1.7%, p < 0.05). Interindividual variation in the urinary excretion of O-desmethyl-angolensin (O-DMA) was also apparent (76-fold after the high-isoflavone treatment period), but there was no relationship between equol excretion and O-DMA excretion. Enterolactone was the major lignan metabolite in urine and plasma but showed less interindividual variation than equol and O-DMA. It is suggested that the dietary fat intake decreases the capacity of gut microbial flora to synthesize equol.