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

Genistein decreases food intake, body weight, and fat pad weight and causes adipose tissue apoptosis in ovariectomized female mice

Genistein, an isoflavone in soybean products, has estrogenic activity and is used as a natural substitute for estrogen replacement therapy in postmenopausal women. Genistein was also shown to decrease fat pad weight in female mice. The primary objective of this study was to determine the effect of genistein on adipose tissue apoptosis in vitro and in vivo. 3T3-L1 preadipocytes and mature adipocytes were treated with 0, 1, 10, 100, and 400 micromol/L genistein and then assayed for apoptosis, whereas only mature adipocytes were assayed for viability. Mature adipocytes treated with genistein demonstrated a dose-related increase in apoptosis. Ovariectomized female mice (9 mo old) were given 0, 150, or 1,500 mg/kg genistein in the semipurified phytoestrogen-free casein-based diet for 3 wk (n=10). After mice were killed, body composition was determined by dual-energy X-ray absorptiometry analysis, and parametrial (PM), inguinal (ING), and retroperitoneal (RP) fat pads were weighed and assayed for apoptosis (% DNA fragmentation). Genistein (1500 mg/kg) reduced food intake (FI) by 14% (P<0.01) and body weight (BW) by 9% (P<0.01). Body composition was not significantly affected, but PM and ING weights were decreased 22% (P<0.05) and 19% (P<0.07), respectively, by 1,500 mg/kg genistein. Apoptosis in ING fat was increased 290% (P<0.05) by 1,500 mg/kg genistein. These findings show that oral genistein treatment can reduce BW, mobilize body fat, and induce apoptosis of adipose tissue in ovariectomized female mice. Thus, genistein may be useful in treating or preventing increased adiposity after menopause.

Critical review of health effects of soyabean phyto-oestrogens in post-menopausal women

A consensus view of soyabean phyto-oestrogens in clinical interventions in post-menopausal women is presented that is based on data from the EU-funded project Phytohealth. The phyto-oestrogens, primarily genistein and daidzein, were given as soyabean-protein isolates, whole-soyabean foods or extracts, supplements or pure compounds. A comprehensive literature search was conducted with well-defined inclusion or exclusion criteria. For areas for which substantial research exists only placebo-controlled double-blind randomised controlled trials (RCT) conducted on healthy post-menopausal women were included. For emerging areas all available human studies in post-menopausal women were reviewed. In order to make cross comparisons between studies the doses of isoflavones were calculated as aglycone equivalents. There is a suggestion, but no conclusive evidence, that isoflavones from the sources studied so far have a beneficial effect on bone health. The consumption of whole-soyabean foods and soyabean-protein isolates has some beneficial effects on lipid markers of cardiovascular risk. The consumption of isolated isoflavones does not affect blood lipid levels or blood pressure, although it may improve endothelial function. For menopausal symptoms there is currently limited evidence that soyabean-protein isolates, soyabean foods or red-clover (Trifolium pratense L.) extract are effective but soyabean isoflavone extracts may be effective in reducing hot flushes. There are too few RCT studies to reach conclusions on the effects of isoflavones on breast cancer, colon cancer, diabetes or cognitive function. The health benefits of soyabean phyto-oestrogens in healthy post-menopausal women are subtle and even some well-designed studies do not show protective effects. Future studies should focus on high-risk post-menopausal women, especially in the areas of diabetes, CVD, breast cancer and bone health.

Plasma and prostate phytoestrogen concentrations in prostate cancer patients after oral phytoestogen supplementation

BACKGROUND

Phytoestrogens have been suggested to reduce the risk of prostate cancer (CaP), but no data exists on how oral phytoestrogen supplementation influences phytoestrogen concentrations in prostate tissue.

METHODS

Forty men with CaP, assigned for radical prostatectomy, received 240 mg of clover phytoestrogens or placebo daily for a 2-week period before their operation in a prospective and randomized study. Phytoestrogens were measured in plasma and prostate tissue by time-resolved fluoroimmunoassay (TR-FIA).

RESULTS

All patients had low baseline phytoestrogen concentrations and only 35% had a detectable plasma concentration of equol. Oral supplementation with phytoestrogens induced a statistically significant (P<0.001) 23- and 7-fold increase in prostate tissue concentrations of the phytoestrogens genistein and daidzein, respectively. Supplemented patients demonstrated prostate tissue genistein and daidzein concentrations that were over twofold higher than their plasma. Interestingly, even though the placebo group did not receive phytoestrogen challenge, they also demonstrated twofold prostate tissue genistein and daidzein concentrations compared to their plasma values, suggesting that the prostate can concentrate available phytoestrogens. In addition, after the supplementation, 90% of the supplemented patients had a detectable plasma equol concentration.

CONCLUSIONS

We conclude that prostate tissue can concentrate genistein and daidzein. Significant elevation of intraprostatic genistein and daidzein concentrations can be achieved with a short-term dietary phytoestrogen supplementation.

Factors affecting the bioavailability of soy isoflavones in humans after ingestion of physiologically relevant levels from different soy foods

The precise role that isoflavones play in the health-related effects of soy foods, and their potential for adverse effects are controversial. This may be due in part to a lack of basic knowledge regarding their bioavailability and metabolism, particularly as it relates to the soy source. To date, there is little information concerning possible differences in the bioavailability of isoflavones derived from natural soy foods consumed at physiologically relevant intakes and whether age- or gender-related differences influence that bioavailability. In the current study of healthy adults [premenopausal (n = 21) and postmenopausal (n = 17) women and a group of men (n = 21)], we examined the effect of age, gender, and the food matrix on the bioavailability of isoflavones for both the aglycon and glucoside forms that are naturally present in 3 different soy foods, soy milk, textured vegetable protein, and tempeh. The study was designed as a random crossover trial so that all individuals received each of the 3 foods. The dose of isoflavones administered to each individual as a single bolus dose was 0.44 mg/kg body weight. Pharmacokinetic parameters were normalized to mg of each isoflavone ingested per kilogram body weight to account for differences in daidzein and genistein content between the diets. Serum isoflavone concentrations in all individuals and groups increased rapidly after the ingestion of each soy food; as expected, genistein concentrations exceeded daidzein concentrations in serum. In this small study, gender differences in peak concentrations of daidzein were observed, with higher levels attained in women. Consumption of tempeh (mainly isoflavone aglycon) resulted in higher serum peak levels of both daidzein (P < 0.001) and genistein (P < 0.01) and the associated area under the curve (P < 0.001 and P < 0.03, respectively) compared with textured vegetable protein (predominantly isoflavone glucosides). However, soy milk was absorbed faster and peak levels of isoflavones were attained earlier than with the other soy foods. Only 30% of the subjects were equol producers and no differences in equol production with age or gender were observed.

Phyto-oestrogen intake in Scottish men: use of serum to validate a self-administered food-frequency questionnaire in older men

OBJECTIVE

To study dietary intake and serum concentrations of isoflavones in order to provide relative validation of isoflavone intake estimates from the Scottish Collaborative Group - Food-Frequency Questionnaire (SCG-FFQ).

DESIGN

Validation study.

SETTING

Southern Scotland.

METHOD

Dietary intake of isoflavones was estimated using the semiquantitative SCG-FFQ and rank correlation and Kappa statistics were used for the relative validation of intakes against serum isoflavone concentrations in 203 male participants who were population controls in a case-control study of diet and prostate cancer.

RESULTS

The median intake of isoflavones (daidzein and genistein) was 1.0mg/day (l-QR 0.6-1.8). The median serum concentration of genistein was 33.79 nmol/l (I-QR 14.12-64.93), nearly twice that of daidzein (18.00 nmol/l, I-QR 8.26-29.45). Equol was detected in 49% of subjects; in these subjects the median was 0.67 nmol/l (I-QR 0.34-1.51). Isoflavone intake was significantly correlated with serum concentrations of daidzein (p = 0.24, P = 0.001), genistein (p = 0.26, P < 0.001) and total isoflavonoids (sum of daidzein, genistein and equol) ( p = 0.27, P < 0.001). Whereas values for weighted Kappa ranged from 0.16 (P = 0.002) for daidzein and equol combined to 0.22 (P < 0.001) for genistein.

CONCLUSIONS

These results demonstrate the suitability of the SCG-FFQ to rank usual isoflavone intakes in older Scottish men, a population observed to have low consumption of soy foods.

Effects of fermented soy milk on the liver lipids under oxidative stress

AIM

To investigate the effects of fermented soy milk powder on the antioxidative status and lipid metabolism in the livers of CCl4-injected rats.

METHODS

Forty-five healthy male Sprague-Dawley rats were randomly assigned to five groups according to five different diets: control (AIN-76), AIN-76+high-dose fermented soy milk powder, AIN-76+low-dose fermented soy milk powder, AIN-76+high-dose milk yogurt powder and AIN-76+low-dose milk yogurt powder. The experiment lasted for 8 wk. After 4 wk, all the rats received intraperitoneal administration of CCl(4)(0.2 mL/100 g body weight) every week. Total cholesterol (TC), triglyceride (TG), TBARS, ALP, and antioxidative enzymes in the liver were evaluated.

RESULTS

There was also no significant difference in TBARS and antioxidative enzymes in the liver. TC and TG in the groups fed with fermented soy milk powder were generally lower than those fed with casein powder.

CONCLUSION

Consumption of fermented soy milk was positive in lowering total cholesterol and TG accumulation in the liver under CCl(4)-induced oxidative stress.

Sensitive high-performance liquid chromatographic method using coulometric electrode array detection for measurement of phytoestrogens in dried blood spots

As the epidemiological and physiological investigation of isoflavones and lignans expands, the need for sensitive methods for analyzing large numbers of samples intensifies. We have developed a method using high-performance liquid chromatography (HPLC) equipped with a coulometric electrode array detector for separation and sensitive detection of daidzein (Da), equol (Eq), genistein (Ge) and enterolactone (Enl) in dried blood spots (DBS). Detection limits ranged from 4.5 pg or 0.09 ng/mL (Eq) to 19 pg or 0.38 ng/mL (Ge) on column. Signal linearities ranged from detection limits to 200 ng/mL (Eq, Enl) and 600 ng/mL (Da, Ge) sample concentration. Correlations between DBS and serum concentrations were 0.66 (Enl), 0.88 (Eq), 0.98 (Ge) and 0.99 (Da). Intra-assay coefficients of variation (CVs) were less than 8% and inter-assay CVs ranged from 2.4 to 20.2% for Da, Eq and Ge for three levels of controls. Enl intra-assay CV was 13.6% for the low pooled control. Analytic recovery ranged from 87% (inter-assay Ge) to 98% (inter-assay Enl). DBS concentrations of Da, Ge and Eq were stable for at least 8 weeks at 4 and 25 degrees C, and at 37 degrees C for at least 5 weeks, with Enl showing greater variability at all temperatures but relative stability for 7 weeks. Measurement of samples from 135 perimenopausal Japanese women consuming habitual diets in Kyoto and Fukushima prefectures showed the former to have the expected lower concentrations of Da and Eq (416 and 87 nM) as well as Enl (49 nM) compared to the latter locale (566, 145 and 72 nM, respectively). This method could be useful in large epidemiological research or detailed physiological studies.

Association of serum phytoestrogen concentration and dietary habits in a sample set of the JACC Study

BACKGROUND: Phytoestrogens may be associated with a reduced risk of hormone dependent neoplasms such as prostate and breast cancers. We tried to determine the validity of the association between serum phytoestrogen concentrations and dietary habits obtained from a food frequency questionnaire used in the Japan Collaborative Cohort Study (JACC Study) for Evaluation of Cancer Risk sponsored by the Ministry of Education, Science, Sports and Culture of Japan (Monbusho).

METHODS: The subjects were 151 male controls who were selected for a nested case-control study for evaluating prostate cancer risk as part of the JACC Study. Dietary habits were determined using a food frequency questionnaire at baseline, and the concentrations of genistein, daidzein, and equol in frozen-stored serum samples assayed in 2002 were compared.

RESULTS: Tofu intake showed a significant association with the serum concentrations of genistein and daidzein (Spearman’s correlation coefficients (r_s) =0.30 and 0.27, respectively), and miso soup showed a slight association with serum concentrations of these phytoestrogens. In contrast, serum concentrations of equol were not associated with dietary intake of tofu and miso soup. After adjustment for serum daidzein concentration, serum equol concentration was associated with the intake of foods containing fat, meat, and coffee, but not green tea.

CONCLUSIONS: Serum genistein and daidzein concentrations were significantly associated with dietary intake of tofu, and slightly with intake of miso soup. Consumption of fat, meat, and coffee may be associated with equol production by intestinal microflora in this sample set.

Fetal exposure to phytoestrogens--the difference in phytoestrogen status between mother and fetus

The goal of this study was to investigate fetal exposure to phytoestrogens, estrogenic compounds derived from plants, by measuring serum concentrations of phytoestrogens in maternal and cord blood. This study included 51 mothers scheduled for cesarean section (C-section), to obtain the serum of mother and fetus at almost the same time. Serum concentrations of phytoestrogens, including genistein (Gen), daidzein (Dai), coumestrol (Cou), equol (Equ; a metabolite of Dai), and sulfate-conjugated Gen, were measured in maternal and cord blood samples by LC-MS/MS and HPLC. It was found that phytoestrogens were transferred from mother to fetus. The detection rates of Gen, Dai, Equ, and Cou in cord serum were 100%, 80%, 35%, and 0%, respectively. Levels of Gen and Dai were higher in cord than in maternal serum (mean=19.4 ng/ml vs.7.2 ng/ml and 4.3 ng/ml vs.1.8 ng/ml for Gen and Dai, respectively). However, a reverse pattern was seen for Equ (cord mean=0.9 ng/ml, maternal mean=2.0 ng/ml). The correlations were significant between the concentration levels of Gen and Dai, Gen and Equ, and Gen and Dai plus Equ in cord serum. However, in maternal serum, the correlations were weak. Also, in 8 of 10 cord serum samples, sulfate-conjugated Gen was detected (mean=5.2 ng/ml, standard deviation=4.7), but it was detected from only one maternal serum (8.7 ng/ml). This study demonstrates placental transfer of phytoestrogens from mother to fetus. It is suggested that the metabolic and/or excretion rates of phytoestrogens are different between mother and fetus and once phytoestrogens are transferred to the fetus, they tend to stay in the fetal side longer than in the maternal side. While the implications for the health and development of the newborn are not known, these data suggest that the effects of fetal exposure to phytoestrogens should be studied further.

Influence of dosage forms on pharmacokinetics of daidzein and its main metabolite daidzein-7-O-glucuronide in rats

AIM

To investigate the influence of dosage forms on the pharmacokinetics of daidzein and its main metabolite daidzein-7-O-glucuronide in Wistar rats.

METHODS

After administration of two typical dosage forms (daidzein solution and suspension), the concentrations of daidzein and daidzein-7-O-glucuronide were determined by an LC-MS-MS method. The pharmacokinetic parameters were calculated and analyzed statistically using the Student's t-test.

RESULTS

Absorption of daidzein after administration of daidzein solution (tmax=0.46 h) was more rapid than that of the suspension (tmax=5.00 h). The peak plasma concentrations of daidzein after administration of daidzein solution and suspension were 601.1 microg/L and 127.3 microg/L, respectively, and those of daidzein-7-O-glucuronide were 3000 microg/L and 192.6 microg/L, respectively. The absolute bioavailabilities of free daidzein in rats after administration of daidzein solution and suspension were 12.8% and 6.1%, respectively, which were calculated to be 47.0% and 12.2%, respectively, in the form of total daidzein (free plus conjugated daidzein).

CONCLUSION

Absorption of daidzein solution was better than absorption of suspension (P<0.05).

Gene Expression Profiling of 17β-Estradiol and Genistein Effects on Mouse Thymus

Estrogen regulates thymic development and involution and modulates immune function. Despite its critical role in thymus, as well as in autoimmune disorders, the mechanism by which estrogen affects the thymus is not well understood. We previously reported that the estrogenic soy isoflavone genistein, as well as 17beta-estradiol (E2), could induce thymic involution, but genistein effects were only partially mediated through estrogen receptors. To provide insights into mechanisms of estrogenic effects in the thymus, we investigated thymic gene expression changes induced by E2 (125 ng/day) and genistein (1500 ppm in feed) in weanling mice using high-density DNA arrays. We identified several E2-responsive genes involved in thymic development and thymocyte signaling during selection and maturation. Functional characterization indicated effects on genes involved in transcription, apoptosis, and the cell cycle. This study also identified changes in several E2-regulated transcripts essential to maintain immune self-tolerance. E2 upregulated more genes than genistein, while genistein downregulated more genes than E2. Though each treatment regulated several genes not altered by the other, there was considerable overlap in the genes regulated by E2 and genistein. Changes in transcription factors and cell cycle factors were consistent with decreases in cell proliferation induced by both genistein and E2. As indicated by the regulation of non-E2-responsive genes, genistein also induced unique effects through non-estrogenic mechanisms. The specific downregulation of the CD4 coreceptor transcript by genistein was consistent with the decline of CD4+ thymocytes in genistein-treated mice in our previous study. This is the first study identifying E2 and genistein target genes in the thymus. These findings provide new mechanistic insights toward explaining estrogen action on thymocyte development, selection, and maturation, as well as the effects of genistein on prenatal and neonatal thymic development and function.

S-equol, a potent ligand for estrogen receptor beta, is the exclusive enantiomeric form of the soy isoflavone metabolite produced by human intestinal bacterial flora

BACKGROUND

The discovery of equol in human urine more than 2 decades ago and the finding that it is bacterially derived from daidzin, an isoflavone abundant in soy foods, led to the current nutritional interest in soy foods. Equol, unlike the soy isoflavones daidzein or genistein, has a chiral center and therefore can occur as 2 distinct diastereoisomers.

OBJECTIVE

Because it was unclear which enantiomer was present in humans, our objectives were to characterize the exact structure of equol, to examine whether the S- and R-equol enantiomers are bioavailable, and to ascertain whether the differences in their conformational structure translate to significant differences in affinity for estrogen receptors.

DESIGN

With the use of chiral-phase HPLC and mass spectrometry, equol was isolated from human urine and plasma, and its enantiomeric structure was defined. Human fecal flora were cultured in vitro and incubated with daidzein to ascertain the stereospecificity of the bacterial production of equol. The pharmacokinetics of S- and R- equol were determined in 3 healthy adults after single-bolus oral administration of both enantiomers, and the affinity of each equol enantiomer for estrogen receptors was measured.

RESULTS

Our studies definitively establish S-equol as the exclusive product of human intestinal bacterial synthesis from soy isoflavones and also show that both enantiomers are bioavailable. S-equol has a high affinity for estrogen receptor beta (K(i) = 0.73 nmol/L), whereas R-equol is relatively inactive.

CONCLUSIONS

Humans have acquired an ability to exclusively synthesize S-equol from the precursor soy isoflavone daidzein, and it is significant that, unlike R-equol, this enantiomer has a relatively high affinity for estrogen receptor beta.

Dietary phytoestrogens and plasma lipids in Dutch postmenopausal women; a cross-sectional study

OBJECTIVE

Isoflavone supplementation in high doses is associated with plasma lipid, glucose and insulin levels. Little is known about the effects of intake within the range of western diets on these endpoints.

DESIGN

We conducted a population-based cross-sectional study in 301 women aged 60-75 years.

METHODS

Dietary isoflavone and lignan intake was assessed with a food frequency questionnaire covering habitual diet during the year preceding enrollment. The outcome measures were total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, Lp(a), fasting glucose and insulin levels. Data were analysed using linear regression and logistic regression models. In the analyses we adjusted for a wide range of potential confounders.

RESULTS

High intake of isoflavones was associated with lower Lp(a) levels (tertile three versus tertile one: odds ratio 0.36, 95% CI 0.16; 0.80). No relation was found between blood levels and the other plasma lipids, glucose or insulin was found.

CONCLUSION

The results of this study suggest that an effect of dietary phytoestrogen intake at low levels on plasma lipid levels is of limited magnitude. It is premature to advise postmenopausal women with low phytoestrogen intake to change their diet towards a phytoestrogen rich diet with the sole aim to prevent cardiovascular disease.

Biofluid 1H NMR-based metabonomic techniques in nutrition research - metabolic effects of dietary isoflavones in humans

A metabonomic approach to nutrition research may provide an insight into in vivo mechanisms of action following nutritional intervention. This approach was applied to investigate changes in the (1)H NMR spectral profile of urine collected from controlled dietary intervention studies conducted in premenopausal women before and following soy or miso consumption. The aim of the study was to identify the biochemical effects of a diet rich in soy isoflavones, phytochemicals which are receiving significant attention because of their potential importance to human health and wide bioactivity in vitro. By applying various chemometric techniques to the data the biochemical effects of conjugated and unconjugated isoflavones were determined. The biochemical changes observed suggest that soy isoflavone ingestion had significant effects on several metabolic pathways associated with osmolyte fluctuation and energy metabolism. These biochemical changes were more significant following ingestion of the unconjugated soy isoflavone (miso) diet suggesting that the chemical composition of the isoflavones present in soy-based foods may have an effect on their biological efficacy in vivo. This study describes a novel application for (1)H NMR analysis by determining subtle differences in biochemical profiles following dietary intervention and providing further insight into the mechanisms of action of phytochemicals in vivo.

Pharmacokinetics of a slow-release formulation of soybean isoflavones in healthy postmenopausal women

Pharmacokinetic studies of soybean isoflavones have shown that following oral ingestion, the two major isoflavones, daidzin and genistin, are hydrolyzed in the intestine, rapidly absorbed into the peripheral circulation, and eliminated from the body with a terminal half-life of 7-8 h. These characteristics make maintenance of steady-state plasma isoflavone concentrations difficult to attain unless there is repeated daily ingestion of foods or supplements containing isoflavones. In an attempt to sustain more constant plasma isoflavone concentrations, a new slow-release formulation of a soybean isoflavone extract was prepared by microencapsulation with a mixture of hydroxypropylcellulose and ethylcellulose to alter its dissolution characteristics. In vitro experiments confirmed slow aqueous dissolution of isoflavones from this formulation when compared with the conventional isoflavone extract. The pharmacokinetics of this slow-release isoflavone extract was studied in 10 healthy postmenopausal women after oral administration of a single capsule containing the equivalent of 22.3 mg of genistein and 7.47 mg of daidzein expressed as aglycons. A comparison of the key pharmacokinetic parameters obtained in this study with those established in extensive studies performed previously in this laboratory indicated that the mean residence time of genistein and daidzein increased 2-fold with microencapsulation. These findings are indicative of a decreased rate of absorption, consistent with the observed slow in vitro dissolution rate. These findings show that it is feasible to employ polymer matrices that slow the aqueous dissolution for preparing sustained-release formulations of soy isoflavones. Further studies to optimize such formulations are warranted.

Human fecal water content of phenolics: the extent of colonic exposure to aromatic compounds

Phenolic compounds are not completely absorbed in the small intestine and so enter the colon, where they might exert physiological effects. To identify phenolics that are present in normal human colon, fecal water was prepared from 5 free-living volunteers with no dietary restrictions and analyzed by gas chromatography-mass spectrometry. Daily measurements were also performed on a single individual to examine the variation more closely. Levels of polyphenols were variable between individuals. Naringenin and quercetin had mean concentrations of 1.20 and 0.63 microM. All other flavonoids examined were present < or =0.17 microM. Simple phenolic and other aromatic acids were present at much higher concentrations. The major components were phenylacetic acid, 479 microM; 3-phenylpropionic acid, 166 microM; 3-(4-hydroxy)-phenylpropionic acid, 68 microM; 3,4-dihydroxycinnamic acid, 52 microM; benzoic acid, 51 microM; 3-hydroxyphenylacetic acid, 46 microM; and 4-hydroxyphenylacetic acid, 19 microM. Other phenolic acids ranged from 0.04 to 7 microM. Decreased dietary phenolic intake caused a decrease in polyphenol and monophenolic acid concentration in fecal water 24 h later. This study is the first to measure the range of aromatic compounds in human fecal water and demonstrates that phenolic acid concentrations are high. The biological effects of phenolics may play an important role in colon function.

Pharmacokinetics of isoflavones, daidzein and genistein, after ingestion of soy beverage compared with soy extract capsules in postmenopausal Thai women

BACKGROUND

Isoflavones from soybeans may provide some beneficial impacts on postmenopausal health. The purpose of this study was to compare the pharmacokinetics and bioavailability of plasma isoflavones (daidzein and genistein) after a single dose of orally administered soy beverage and soy extract capsules in postmenopausal Thai women.

METHODS

We conducted a randomized two-phase crossover pharmacokinetic study in 12 postmenopausal Thai women. In the first phase, each subject randomly received either 2 soy extract capsules (containing daidzin : genistin = 7.79 : 22.57 mg), or soy beverage prepared from 15 g of soy flour (containing daidzin : genistin = 9.27 : 10.51 mg). In the second phase, the subjects received an alternative preparation in the same manner after a washout period of at least 1 week. Blood samples were collected immediately before and at 0.5, 1, 2, 4, 6, 8, 10, 12, 24 and 32 h after administration of the soy preparation in each phase. Plasma daidzein and genistein concentrations were determined by using high performance liquid chromatography (HPLC). The pharmacokinetic parameters of daidzein and genistein, i.e. maximal plasma concentration (Cmax), time to maximal plasma concentration (Tmax), area under the plasma concentration-time curve (AUC) and half-life (t1/2), were estimated using the TopFit version 2.0 software with noncompartmental model analysis.

RESULTS

There were no significant differences in the mean values of Cmax/dose, AUC0-32/dose, AUC0- proportional, variant/dose, Tmax, and t1/2 of genistein between both preparations. For pharmacokinetic parameters of daidzein, the mean values of Cmax/dose, Tmax, and t1/2 did not significantly differ between both preparations. Nonetheless, the mean AUC0-32/dose and AUC0- proportional, variant/dose after administration of soy extract capsules were slightly (but significantly, p < 0.05) higher than those of soy beverage.

CONCLUSION

The bioavailability of daidzein, which was adjusted for the administered dose (AUC/dose), following a single oral administration of soy beverage was slightly (but significantly) less than that of soy extract capsules, whereas, the bioavailability adjusted for administered dose of genistein from both soy preparations were comparable. The other pharmacokinetic parameters of daidzein and genistein, including Cmax adjusted for the dose, Tmax and t1/2, were not different between both soy preparations.

Gut bacterial metabolism of the soy isoflavone daidzein: exploring the relevance to human health

The indigenous intestinal microflora are involved in a variety of processes within the human body, and are important for maintaining host health. As such, interindividual differences in the ability to harbor certain intestinal bacteria might be associated with interindividual differences in health and/or disease susceptibility. In the last decade there has been considerable interest in phytoestrogen intakes in relation to human health. Daidzein, an isoflavone phytoestrogen found in soy, is metabolized to equol and O-desmethylangolensin (O-DMA) by intestinal bacteria. The specific bacterium/bacteria responsible for equol and O-DMA production in humans have yet to be identified definitively, but in vitro and animal studies have suggested that equol and O-DMA are more biologically active than their precursor daidzein. Interestingly, substantial interindividual differences in daidzein metabolism exist; following soy or daidzein consumption, approximately 30%-50% of the human population produce equol, and approximately 80%-90% produce O-DMA. Observational and intervention studies in humans have suggested that the ability to produce equol and O-DMA may be associated with reduced risk of certain diseases including breast and prostate cancers. However, relatively few studies have been conducted to date. In this review, we discuss the available evidence for a relationship between daidzeinmetabolizing phenotypes and human health, and suggest potential mechanisms for some of the reported relationships.

The usual intake of lignans but not that of isoflavones may be related to cardiovascular risk factors in U.S. men

Isoflavone supplementation in the form of soy protein-containing isoflavones is associated with beneficial lipid changes. Information on usual isoflavone and lignan intakes in the diet of Western men and their associations with cardiovascular risk factors is not available. From the Health Professionals Follow-up Study, we selected 468 men, aged 47-83 y, who were free of cardiovascular disease, diabetes, and cancer, and who had provided a blood sample in 1994. We measured circulating total, LDL, and HDL cholesterol, triacylglycerol, lipoprotein(a), apolipoprotein (apo) A1, apoB, hemoglobin (Hb)A1c, insulin, C-peptide, and leptin concentrations. Isoflavone and lignan intakes were calculated from a FFQ. We used multivariate linear regression. None of the cardiovascular risk factors was strongly associated with isoflavone intake. Blood levels of LDL cholesterol and apoB tended to increase with increasing lignan intake [for LDL cholesterol, quartile 4 -quartile 1 = 9% (95% CI 1%; 16%), P for trend = 0.01, and for apo B, quartile 4 -quartile 1 = 9% (95% CI 1%; 16%), P for trend = 0.02]. Fasting insulin and C-peptide tended to decrease with increasing lignan intake [for insulin, quartile 4 -quartile 1 = -11% (95% CI -55%; -8%), P for trend = 0.02, and for C-peptide, quartile 4 -quartile 1 = -25% (95% CI -44; -6%), P for trend = 0.01]. Our results suggest that intake of isoflavones within the range of Western diets is not associated with a cardiovascular risk profile among men. Diets high in lignan intake may increase apoB-containing lipoproteins and decrease fasting insulin secretion, but these findings require confirmation.

Metabolism of antioxidant and chemopreventive ellagitannins from strawberries, raspberries, walnuts, and oak-aged wine in humans: identification of biomarkers and individual variability

Ellagitannins (ETs) are dietary polyphenols, containing ellagic acid (EA) subunits, with antioxidant and cancer chemopreventive activities that might contribute to health benefits in humans. However, little is known about their metabolic fate. We investigate here the metabolism of different dietary ETs and EA derivatives in humans. Forty healthy volunteers were distributed in four groups. Each group consumed, in a single dose, a different ET-containing foodstuff, i.e., strawberries (250 g), red raspberries (225 g), walnuts (35 g), and oak-aged red wine (300 mL). After the intake, five urine fractions (F) were collected at 8 (F1), 16 (F2), 32 (F3), 40 (F4), and 56 (F5) h. Neither ETs nor EA were detected in urine after LC-MS/MS analysis. However, the microbial metabolite 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one (urolithin B) conjugated with glucuronic acid was detected along the fractions F3-F5 in all of the subjects, independently of the consumed foodstuff. The mean percentage of metabolite excretion ranged from 2.8 (strawberries) to 16.6% (walnuts) regarding the ingested ETs. Considerable interindividual differences were noted, identifying "high and low metabolite excreters" in each group, which supported the involvement of the colonic microflora in ET metabolism. These results indicate that urolithin B (a previously described antiangiogenic and hyaluronidase inhibitor compound) is a biomarker of human exposure to dietary ETs and may be useful in intervention studies with ET-containing products. The antioxidant and anticarcinogenic effects of dietary ETs and EA should be considered in the gastrointestinal tract whereas the study of potential systemic activities should be focused on the bioavailable urolithin B derivatives.

Screening of the inhibitory effect of vegetable constituents on the aryl hydrocarbon receptor-mediated activity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The aryl hydrocarbon receptor (AhR) is a ligand-activated nuclear transcription factor that mediates responses to environmental contaminants such as dioxins, which have many adverse health effects. We performed a preliminary screening of the inhibitory effects of vegetable constituents on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced activation of AhR using the AhR-based bioassay for dioxins, the Ah-Immunoassay. Ninety vegetable constituents including flavonoids, tannins, saponins, terpenes, etc., were assayed in vitro. Among them, flavones, flavonols, anthraquinones, piperine, coumestrol, brevifolincarboxylic acid, and resveratrol showed marked inhibitory effects on AhR-based bioassay activation by TCDD, and their effects were dose dependent. Curcumin, carnosol, and capsaicin also inhibited the activation of AhR in this assay, although to a lesser degree. These results suggest that several vegetable constituents might play a role in protection against dioxin toxicity.

Hepatic gene expression profiles are altered by genistein supplementation in mice with diet-induced obesity

We reported previously that genistein enhances the expression of genes involved in fatty acid catabolism through activation of peroxisome proliferator-activated receptor (PPAR) alpha in HepG2 cells, suggesting that genistein holds great promise for therapeutic applications to lipid abnormalities such as obesity and hyperlipidemia in humans. In this study, we examined the changes in hepatic transcriptional profiles using cDNA microarrays in mice with high-fat diet (HFD)-induced obesity supplemented with genistein. C57BL/6J male mice (n = 10/group) were fed a low-fat diet (LFD), a HFD, or a HFD supplemented with 2 g/kg genistein (HFD+GEN) for 12 wk. Mice fed the HFD had abnormal lipid profiles and significantly greater body weight and visceral fat accumulation than the LFD-fed group. Genistein supplementation improved lipid profiles and hepatic steatosis and attenuated the increases in body weight and visceral fat in HFD-fed mice. The cDNA microarrays revealed marked alterations in the expression of 107 genes in the mice fed the HFD and/or the HFD+GEN. Of 97 transcripts altered in the HFD-fed group, 84 genes were normalized by genistein supplementation. However, several genes involved in fatty acid catabolism were not normalized but were still upregulated in the HFD+GEN-fed group, relative to the LFD-fed group. Furthermore, carnitine O-octanoyltransferase, which accelerates fatty acid oxidation, was not affected by the HFD, but was induced by genistein supplementation. These results are consistent with our previous study showing that genistein is an activator of PPAR alpha in vitro. This study showed beneficial effects of genistein supplementation in preventing the development of obesity and metabolic abnormalities in mice with diet-induced obesity. Our results also provide interesting information about the genes associated with the beneficial effects of genistein as well as the mechanisms underlying the development and maintenance of the obesity phenotype in vivo.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

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.

Biphasic effect of daidzein on cell growth of human colon cancer cells

Colorectal cancer is one of the most common cancers in the world, poorly responding to available chemotherapeutic agents. To investigate whether natural molecules can inhibit colon cancer progression, we investigated a principle phytoestrogen found in soybean known as daidzein, and determined its effects on the human colon cancer cell line LoVo. LoVo cells were treated with 0.1, 1, 5, 10, 50 and 100 microM daidzein for 2, 3, 4 or 5 d. The results indicated that daidzein stimulated the growth of LoVo cells at 0.1 and 1 microM whereas at higher concentrations (10, 50 and 100 microM) cell growth was inhibited in a dose-dependent manner. Treatment of daidzein at 10, 50 and 100 microM resulted in cell cycle arrest at G0/G1 phase, DNA fragmentation and increases in caspase-3 activity. There were no changes in alkaline phosphatase activity (ALP), an indicator of cell differentiation, upon treatment with daidzein when compared to controls. These results indicate that daidzein has a biphasic effect on LoVo cell growth and its tumor suppressive effect is by means of cell cycle arrest and apoptosis but not through cell differentiation.

The apparent absorptions of isoflavone glucosides and aglucons are similar in women and are increased by rapid gut transit time and low fecal isoflavone degradation

We hypothesized that there would be no difference in apparent absorption, as assessed by urinary excretion, between isoflavone sources rich in glucosides or aglucons and that subjects with rapid gut transit time (GTT) and low fecal isoflavone degradation phenotype would absorb more isoflavones. Women (n = 13) with a fecal daidzein degradation rate constant, D(k) > 0.30 h(-1) (high degraders) and GTT of 106 +/- 11 h and women (n = 12) with D(k) < 0.20 h(-1) (low degraders) and GTT of 71 +/- 12 h were randomly assigned to 3 treatments: soygerm (1.1 micromol/kg body weight, n = 5 high degraders, 4 low degraders), fermented soygerm (3.3 micromol/kg, n = 4 high and 4 low degraders) or Novasoy isoflavone extract (1.5 micromol/kg, n = 4 high and 4 low degraders) for 7 d. By HPLC analysis, 24-h urinary excretion of soygerm was greater than Novasoy (51 +/- 6 vs. 26 +/- 6% of ingested dose, P < 0.05). Women of the low daidzein degradation phenotype had greater urinary isoflavone excretion than did women of the high daidzein degradation phenotype (51.6 +/- 4.8 vs. 33.8 +/- 4.7%, P < 0.05, mean of d1 and 7). The plasma total isoflavone level (estimated as a percentage of the ingested amount, mean of d 1 and 7) differed between women who consumed fermented soygerm and soygerm 3 h after feeding (1.8 +/- 0.3 vs. 0.5 +/- 0.3%, P < 0.05). Urinary excretions of aglucons and glucosides did not differ. The study confirmed that rapid GTT and low fecal isoflavone degradation rate increased the apparent absorption of isoflavones.

Biotransformation of soy isoflavone-glycosides in laying hens: intestinal absorption and preferential accumulation into egg yolk of equol, a more estrogenic metabolite of daidzein

Dietary soy-isoflavones have recently been noted as phytoestrogens with potentially beneficial effects on human health, and they are biologically transformed in the intestinal tract into aglycones and further into several specific metabolites. Here we report that in laying hens daidzin, a soy isoflavone-glycoside, in the diet was transformed into equol, absorbed, transported in circulating peripheral blood, and preferentially accumulated into egg yolk in its conjugated form. Laying hens were fed experimental diets containing two levels of soy isoflavone-glycosides (177 or 528 mg per 100 g diet) for 21 or 42 days, and blood and eggs were collected at 1- to 9-day intervals. HPLC analyses revealed that most of the isoflavones (daidzein, glycitein, and genistein) and a metabolite, equol, were present in blood and egg yolk in conjugated form. The concentration of equol-conjugates in blood plasma and egg yolk was higher than any of the other three isoflavone-conjugates analyzed and, especially in egg yolk, the equol-conjugates comprised no less than 60% of the total isoflavone-conjugates. The isoflavones, including equol, distributed mostly (95%) in the high-density fraction of blood serum, and more (65%) in the granule fraction of egg yolk. These results raise the possibility that feeding domestic animals soy-based fodder produces animal-based foods rich in a more active form of phytoestrogens.

Soy isoflavone intake lowers serum LDL cholesterol: a meta-analysis of 8 randomized controlled trials in humans

Clinical trials have noted hypocholesterolemic effects of soy protein intake, but the components responsible are not known. This meta-analysis of 8 randomized controlled trials was conducted to more precisely evaluate the effects of isoflavones on blood LDL cholesterol concentration independently of soy protein level. PubMed was searched for English-language "randomized controlled trial" articles published from 1966 to 2003 that described the effects of soy protein isolate (SPI) intake with measured isoflavone levels on blood lipids in humans using the search terms "soy protein," "isoflavones," and "cholesterol." From 31 articles identified by the search, 8 articles (with 10 low vs. high isoflavone comparisons) were selected for the meta-analysis. Subjects in each comparison consumed similar dietary fat, cholesterol, and fiber; the reported body weight of subjects did not change significantly during treatment. Serum LDL cholesterol concentration in subjects who consumed SPI (mean 50 g/d) with high isoflavone content (mean intake 96 mg/d) decreased by 0.15 mmol/L (95% CI: 0.08 to 0.23 mmol/L; P < 0.0001) compared with those who consumed the same SPI level with low isoflavone content (mean intake 6 mg/d). Decreases in serum LDL cholesterol concentration in hypercholesterolemic and normocholesterolemic subjects were 0.18 mmol/L (95% CI: 0.01 to 0.35 mmol/L; P = 0.03) and 0.14 mmol/L (95% CI: 0.06, 0.23 mmol/L; P = 0.0008), respectively. With identical soy protein intake, high isoflavone intake led to significantly greater decreases in serum LDL cholesterol than low isoflavone intake, demonstrating that isoflavones have LDL cholesterol-lowering effects independent of soy protein.

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.

Dietary phytoestrogens and vascular function in postmenopausal women

OBJECTIVE

To investigate the effects of low levels of intake of phytoestrogens in Western habitual diet on vascular function.

DESIGN

A cross-sectional study.

SETTING

A population-based study.

PARTICIPANTS

A total of 301 postmenopausal women aged 60-75 years living in The Netherlands. DETERMINANT: Dietary phytoestrogen intake as assessed using a food frequency questionnaire covering the year prior to enrollment.

MAIN OUTCOME MEASURES

Blood pressure, hypertension, endothelial function and ankle brachial index.

RESULTS

The median isoflavone intake was 0.2 mg in the lowest tertile and 11.4 mg in the highest tertile. Median lignan intake was 0.8 and 2.2 mg, respectively. No associations were found for higher intake of isoflavones, systolic and diastolic blood pressures, ankle-arm blood pressure index, endothelial function or hypertension. For lignans no association was found for ankle-arm blood pressure index or endothelial function, but we did observe lower systolic and diastolic blood pressures and a lower prevalence of hypertension (systolic blood pressure difference T3-T1, -11.2 mmHg, 95% confidence interval = -17.8 to -4.5, P for trend = 0.001; diastolic blood pressure difference T3-T1, -3.6 mmHg, 95% confidence interval = -7.8 to 0.6, P for trend = 0,08; and prevalence of hypertension, odds ratio T3 versus T1 = 0.41, 95% confidence interval = 0.22-0.76, P for trend over tertiles = 0.004).

CONCLUSION

The results of this study suggest a protective effect of dietary lignan intake on blood pressure and hypertension, even at low levels.

Evidence for genistein mediated cytotoxicity and apoptosis in rat brain

The effects of chronic treatment with high doses of genistein, a major isoflavone of soybeans and soy-based products, have yet to be determined and what is known remains controversial. The present study was undertaken to investigate the cytotoxic effects of chronic ingestion of genistein on rat brain in vivo and the observations were compared with results from in vitro studies with primary cultures of cortical neurons. Sprague-Dawley rats were given 2 or 20 mg/day genistein (p.o.) for four weeks. The high dose of genistein (20 mg/day) significantly increased lactate dehydrogenase (LDH) in rat brain tissue homogenates, whereas the low dose of genistein (2 mg/day) decreased LDH. In addition, DNA fragmentation was detected in homogenates of brain tissue from rats receiving either dose of genistein. These results are consistent with those of in vitro studies indicating that high concentrations of genistein caused cytotoxicity and DNA ladder formation in primary cultures of cortical neurons. Genistein decreased the expression of the 32 kDa caspase-3 precursor and increased the levels of cleaved caspase-3 (18 kDa) in both rat brain tissue homogenates and in primary cultures of cortical neurons. Furthermore, expression of poly (ADP-ribose) polymerase (PARP) was also decreased in both experimental systems. These results suggest that chronic administration of genistein at high doses may induce cytotoxicity and apoptosis in the rat brain.

Genistein enhances expression of genes involved in fatty acid catabolism through activation of PPARalpha

Although evidences are emerging that dietary isoflavones have beneficial effects in treatment of hyperlipidemia and cardiovascular diseases, the underlying molecular mechanism has not yet been extensively characterized. In this report, we showed that genistein, one of the major isoflavones, increased expression of genes involved in lipid catabolism such as carnitine palmitoyltransferase 1, liver form (CPT1L) in HepG2 cells, when assayed by real-time reverse-transcriptase polymerase chain reactions as well as Western blotting analysis. The increase in mRNA-level of CPT1L after genistein treatment was not changed in the presence of ICI182780, a potent inhibitor of estrogen receptor, suggesting that this effect of genistein was estrogen receptor-independent. Since these genes involved in fatty acid catabolism are considered putative downstream target genes of peroxisome proliferators-activated receptor alpha (PPARalpha), we examined whether expression of PPARalpha was modulated by genistein treatment. Interestingly, genistein induced expression of PPARalpha at both mRNA- and protein-level. Further, genistein activated transcriptional activity of PPARalpha, when determined by reporter gene analysis, suggesting genistein as a potential ligand for PPARalpha. Taken together, this study provides a picture of the regulatory action of genistein, as an activator of PPARalpha in fatty acid catabolism and potential use of genistein as lipid-lowering agent.

LC/UV/ESI-MS analysis of isoflavones in Edamame and Tofu soybeans

High-performance liquid chromatography coupled with ultraviolet and electrospray ionization mass spectrometry (HPLC/UV/ESI-MSD) was applied to the study of isoflavones in both Edamame and Tofu soy varieties, from which the immature fresh soybeans or the mature soybean seeds are consumed, respectively. Positive atmospheric pressure interface (API) MS and MS/MS were used to provide molecular mass information and led to the identification of a total 16 isoflavones, including three aglycones, three glycosides, two glycoside acetates, and eight glycoside malonates. The major isoflavones in soybean seeds were daidzein and genistein glycoside and their malonate conjugates. Trace levels of daidzein and genistein acetyl glycosides were found only in the mature dry soybean seeds. To facilitate quantitative analysis, acid hydrolysis during extraction of soy samples was selected to convert the various phytoestrogen conjugates into their respective isoflavone aglycones, allowing accurate quantitation of total phytoestrogens as aglycones. On the basis of HPLC combined with UV and MS detection, all three targeted soy isoflavone aglycones, daidzein, genistein and glycitein in hydrolyzed extracts were successfully quantified within 25 min with formononetin used as the internal standard. The standard curves of UV detection were fitted in the range of 14.16-29000 ng/mL for daidzein, 15.38-31500 ng/mL for genistein, and 11.72-24000 ng/mL for glycitein. For MS detection, the standard curves were established in the range of 3.54-1812.5 ng/mL for daidzein, 3.85-1968.75 ng/mL for genistein, and 2.93-1500 ng/mL for glycitein. Good linearities (r(2) > 0.999 for UV and r(2) > 0.99 for MS) for standard curves were achieved for each isoflavone. The accuracy and precision (RSD) were within 10% for UV detection and 15% for MS detection (n = 10). Using this method, the phytoestrogen levels of total isoflavone aglycones from 30 soybean seed varieties were then evaluated for confirmation of the technique. Total isoflavones ranged across the varieties from 0.02 to 0.12% in the Edamame varieties, which are harvested while the seeds are still immature, and from 0.16 to 0.25% in Tofu varieties, harvested when the seeds are physiologically mature. While the literature has focused on the isoflavone content of soy products and processing soy, this report provides a reliable analytical technique for screening of authenticated fresh immature Edamame soybeans and Tofu soybeans.

Influence of soya-based infant formula consumption on isoflavone and gut microflora metabolite concentrations in urine and on faecal microflora composition and metabolic activity in infants and children

The urinary excretion of soya isoflavones and gut microflora metabolites was investigated in infants and children who had been fed soya-based infant formulas in early infancy. These infants and children were compared with cows'-milk formula-fed controls, to determine at what age gut microflora metabolism of daidzein to equol and/or O-desmethylangolensin (O-DMA) was established, and whether exposure to isoflavones in early infancy influences their metabolism at a later stage of development. Sixty infants and children (aged 4 months-7 years) participated in the study; thirty in each of the soya and control groups. There were four age groups. These were: 4-6 months (seven in the soya group and seven in the control group); 7-12 months (seven in the soya group and nine in the control group); 1-3 years (six in the soya group and eight in the control group); 3-7 years (ten in the soya group and six in the control group). Urine samples were collected to measure isoflavonoids by MS, and faecal samples were collected to measure gut-health-related bacterial composition, by fluorescent in situ hybridisation with oligonucleotide probes, and metabolic activity. A soya challenge (typically a soya yoghurt alternative product containing 4.8 g soya protein and on average 22 mg total isoflavones) was given to control-group infants (>6 months) and children, and also to soya-group children that were no longer consuming soya, to determine their ability to produce equol and/or O-DMA. Urinary genistein, daidzein and glycitein were detected in all infants (4-6 months) fed soya-based infant formula; O-DMA was detected in 75 % of infants but equol was detected in only 25 %. In the controls (4-6 months), urinary isoflavonoids were very low or not detected. In the older age groups (7 months-7 years), O-DMA was found in the urine samples of 75 % of the soya group and 50 % of the controls, after the soya challenge. Equol excretion was detected in 19 % of the soya-group infants and children, and in only 5 % of the controls. However, in the oldest (3-7 years) children, the proportion excreting O-DMA and equol was similar in both groups. Faecal bacterial numbers for bifidobacteria (P<0.001), bacteroides and clostridia (P<0.05) were significantly lower for the soya group compared with the control group. There appears to be no lasting effect of early-life isoflavone exposure on isoflavone metabolism.

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.

Not all soy products are created equal: caution needed in interpretation of research results

Interest in the health benefits of soy foods has been intense among the research community, health professionals, and the public. At the same time, potential concerns associated with soy consumption, especially as related to soy isoflavones, have tempered the enthusiasm for making public health recommendations. On both accounts, the primary soybean isoflavone, genistein, has received the most attention. Because consumers are becoming increasingly confused by the often conflicting dietary messages, a balanced and accurate view of the risks and benefits of soy foods and soy food components is essential. Even among health professionals, confusion exists about proper nomenclature and about the precise composition of the agents under investigation. Levels of isoflavones are frequently assumed to be constant within categories of soy foods, and intakes are estimated rather than being directly analyzed. Furthermore, all too often research dealing singularly with genistein is interpreted by both health professionals and the media as equating directly with soy. Researchers often fail to fully understand the implications of their research outcomes and the context in which those outcomes should be placed. With the hundreds of publications yearly on soy and isoflavones, it is especially important to consider the literature in its entirety when making pronouncements about health effects. Efforts are needed by all to reduce the public confusion by adapting standardized approaches to the reporting of data. This paper provides a framework for both standardization of nomenclature and appropriate interpretation of data.

Serum phytoestrogens and prostate cancer risk in a nested case-control study among Japanese men

The purpose of this study was to examine whether a high serum concentration of phytoestrogens reduces the risk of prostate cancer in a case-control study nested in a community-based cohort in Japan (Japan Collaborative Cohort (JACC) Study). Information on lifestyles and sera of the subjects were collected in 1988-90, and they were followed up to 1999. Incident and dead cases of prostate cancer and controls were matched for study area and age. Phytoestrogens and sex hormones in sera stored at - 80 degrees C were measured in 2002. Of 14,105 male subjects of the cohort who donated their sera, 52 cases and 151 controls were identified. Three datasets were analyzed; 1) all subjects, 2) 40 cases and 101 controls after excluding subjects with low testosterone levels who were suspected of having had medical intervention, and 3) 28 cases and 69 controls with prostate specific antigen level of Collapse

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MESH Headings

• Adult
• Biomarkers, Tumor/blood
• Case-Control Studies
• Humans
• Isoflavones/blood
• Japan
• Male
• Middle Aged
• Odds Ratio
• Phytoestrogens
• Plant Preparations/blood
• Prostatic Neoplasms/blood
• Risk Factors

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Grants Collapse

Affiliation(s)

Kotaro Ozasa Department of Epidemiology for Community Health and Medicine, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kamigyo-ku, Kyoto 602-8566, Japan.
Masahiro Nakao
Yoshiyuki Watanabe
Kyohei Hayashi
Tsuneharu Miki
Kazuya Mikami
Mitsuru Mori
Fumio Sakauchi
Masakazu Washio
Yoshinori Ito
Koji Suzuki
Kenji Wakai
Akiko Tamakoshi

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Effects of isoflavone supplements on bone metabolic markers and climacteric symptoms in Japanese women

A double-blind, placebo-controlled crossover study on the effects of 40~mg/d isoflavone supplements was carried out by 58 climacteric Japanese women. A questionnaire and an interview concerning climacteric symptoms, health status, dietary and exercise habit, and medical history were carried out, and the physical check-up and biochemical tests including sex-hormone analysis were made at baseline and after 4 and 8 weeks of treatment. Urinary isoflavones were separately measured from the frozen samples. Isoflavone treatment did not cause any adverse effects on anthropometric measures or blood chemistry. Urinary deoxypyridinoline, a marker of bone resorption decreased significantly with isoflavone treatment. This tendency was remarkable among equol producers. Plasma osteocalcin and bone mineral density did not change by the four-weeks treatment. As for climacteric symptoms, hot flash decreased significantly. Systolic and diastolic blood pressure of hypertensive participants decreased significantly after isoflavone treatment compared with baseline and the placebo treatment. Isoflavone supplementation offers benefits to reduce effectively on bone resorption enhanced by menopause. The treatment also showed an improvement of climacteric hot flash and hypertension. Equol producers showed better results.

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.

Genotoxic activity of four metabolites of the soy isoflavone daidzein

Products containing phytoestrogens are increasingly promoted as the "natural" alternative to estrogen replacement therapy. In the present study, we have used the in vitro micronucleus assay in L5178Y mouse lymphoma cells to investigate the genotoxic potential of the isoflavone daidzein, and of four daidzein metabolites known to be formed in humans. Whereas no induction of micronuclei was observed with daidzein up to the limit of solubility (100 microM), all four daidzein metabolites, i.e. equol (2.3-fold induction at 100 microM), O-desmethylangolensin (6.2-fold induction at 10 microM), 4',6,7-isoflavone (6.7-fold induction at 100 microM) and 3',4',7-isoflavone (8.2-fold induction at 100 microM) induced micronuclei in a concentration-dependent manner. Thus, both reductive and oxidative metabolites of the soy isoflavone daidzein exhibit genotoxic potential in vitro.

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

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

The soy isoflavone genistein decreases adipose deposition in mice

Adipose tissue is responsive to estrogen and expresses both estrogen receptor alpha and beta. To test the hypothesis that the estrogenic soy isoflavone genistein can have effects on adipose tissue, juvenile or adult C57/BL6 mice were ovariectomized and given daily injections of vehicle, 17beta-estradiol (5 microg/kg.d) or genistein (8-200 mg/kg.d) sc for 21-28 d. To test effects of dietary genistein, 25- to 27-d-old mice were fed diets containing 0-1500 parts per million (ppm) genistein for 12 d. Mice were killed and fat pads weighed. Parametrial fat pads were used for morphometric and Northern analysis. Genistein injections decreased adipose weight and adipocyte circumference at higher doses; effects in adult and juvenile mice were similar. Genistein decreased lipoprotein lipase mRNA, which may be a critical aspect of its adipose effects. Juveniles fed 500-1500 ppm dietary genistein had dose-responsive decreases in fat pad weights of 37-57%, compared with controls; 300 ppm genistein did not cause decreases. Genistein doses of 300, 500, 1000, and 1500 ppm produced serum genistein concentrations of 1.02 +/- 0.14 microM, 1.79 +/- 0.32 microM, 2.55 +/- 0.18 microM, and 3.81 +/- 0.39 microM, respectively. These results indicate dietary genistein at 500-1500 ppm produces antilipogenic effects in mice at serum levels that humans are realistically exposed to.

Evidence for the involvement of human liver microsomes CYP1A2 in the mono-hydroxylation of daidzein

BACKGROUND

In vitro studies with rats and human liver microsomes (HLM) demonstrated that daidzein is readily metabolized to mono-hydroxylated compounds. In this study, daidzein mono-hydroxylated metabolites was investigated using human liver microsomes to identify the cytochrome P450 (CYP) isoform(s) involved in this metabolic pathway.

METHODS

Kinetic analysis for the formation rates of mono-hydroxylated metabolites of daidzein, including 7,8,4'-trihydroxyisoflavone (7,8,4'-THI), 7,3,4'-trihydroxyisoflavone (7,3,4'-THI) and 6,7,4'-trihydroxyisoflavone (6,7,4'-THI), were performed using human liver microsomes (HLM) and recombinant enzymes at substrate concentrations ranging from 0.5 to 400 micromol/l. Nine selective inhibitors or substrate probes specific for different CYP isoforms were applied for screening the isoform(s) responsible for mono-hydroxylated metabolism of daidzein.

RESULTS

Michaelis-Menten kinetic parameters were best fitted to a one-component enzyme kinetic model. The mean K(m) (micromol/l) and V(max) (micromol/g min) values (+/-S.D.) were 26.86 (10.45) and 4.76 (2.07), 53.83 (22.25) and 2.29 (1.04), 51.48 (29.32) and 2.21(0.82), for the formation rates of 7,8,4'-THI, 7,3',4'-THI and 6,7,4'-THI, respectively. Furafylline, the CYP1A2-specific inhibitor, estrogen and monoclonal antibody raised against human CYP1A2 (MAB-1A2) substantially inhibited the formation rates of mono-hydroxylated metabolites. The IC(50) of Fur for the formation of 7,3',4'-THI, 6,7,4'-THI and 7,8,4'-THI was 1.0, 0.9 and 0.8 micromol/l, respectively. The IC(50) of estrogen for the formation of 7,3',4'-THI, 6,7,4'-THI and 7,8,4'-THI was 51, 60 and 64 micromol/l, respectively. The IC(50) of MAB-1A2 for the formation of the mono-hydroxylated products was 1 micromol/l, but neither other selective inhibitor nor substrate probes, including coumarin (CYP2D6), sulphaphenzole (CYP2C9/10), omeprazole (CYP2C19), quinidine (CYP2D6), diethyldithiocarbamate (CYP2E1), troleandomycin (CYP3A4) and keteconazole (CYP3A4), did so with human liver microsomes.

CONCLUSION

Daidzein mono-hydroxylated products are principally metabolized by CYP1A2 in human.

Stability and bioaccessibility of isoflavones from soy bread during in vitro digestion

The impact of simulated digestion on the stability and bioaccessibility of isoflavonoids from soy bread was examined using simulated oral, gastric, and small intestinal digestion. The aqueous (bioaccessible) fraction was isolated from digesta by centrifugation, and samples were analyzed by high-performance liquid chromatography (HPLC). Isoflavonoids were stable during simulated digestion. Partitioning of aglycones, acetylgenistin, and malonylgenistin into the aqueous fraction was significantly (P < 0.01) affected by the concentration of bile present during small intestinal digestion. Omission of bile resulted in nondetectable genistein and <40% of total daidzein, glycitein, and acetylgenistin in the aqueous fraction of digesta. Partitioning of these compounds into the aqueous fraction was increased by physiological concentrations of bile extract. These results suggest that micellarization is required for optimal bioaccessibility of isoflavonoid aglycones. We propose that the bioavailability of isoflavones from foods containing fat and protein may exceed that of supplements due to enhanced bile secretion.