Toxicokinetics of the phytoestrogen daidzein in female DA/Han rats

Mucin coated protein-polyphenol microcarriers for daidzein delivery

Daidzein, an isoflavone found abundantly in legumes, may benefit from bypassing upper gut absorption to reach the colon where it can be metabolized into the potent estrogen equol by the gut microbiome. To achieve this, we developed mucin coated protein-tannin multilayer microcarriers. Highly porous functionalized calcium carbonate (FCC) microparticles efficiently absorbed daidzein from a dimethyl sulfoxide solution, with a loading capacity of 21.6 ± 1.8 wt% as measured by ultra-high pressure liquid chromatography - mass spectrometry (UPLC-MS). Daidzein-containing FCC microparticles were then coated with a bovine serum albumin (BSA)-tannin n-layer film terminated with mucin ((BSA-TA)n-mucin) by layer-by-layer deposition from corresponding aqueous solutions followed by FCC decomposition with HCl. Raman spectroscopy confirmed mucin-tannin complexation involving both hydrophobic interactions and hydrogen bonding. The resulting multilayer microcarriers contained 54 wt% of nanocrystalline daidzein as confirmed by X-ray diffraction and UPLC-MS. Preliminary screening of several types of mucin coatings using an in vitro INFOGEST digestion model demonstrated that mucin type III from porcine stomach provided the highest protection against upper intestinal digestion. (BSA-TA)8-mucin and (BSA-TA)4-mucin microcarriers retained 71 ± 16.4% and 68 ± 4.6% of daidzein, respectively, at the end of the small intestinal phase. Mucin-free (BSA-TA)8 retained a lower daidzein amount of 46%. Daidzein release and further conversion into equol were observed during in vitro colonic studies with fecal microbiota from a healthy non-equol-producing donor and Slackia equolifaciens. The developed approach has potential for encapsulating other hydrophobic nutraceuticals or therapeutics, enhancing their bioaccessibility in the colon.

Use of Physiologically Based Kinetic Modeling to Predict Rat Gut Microbial Metabolism of the Isoflavone Daidzein to S-Equol and Its Consequences for ERα Activation

SCOPE

To predict gut microbial metabolism of xenobiotics and the resulting plasma concentrations of metabolites formed, an in vitro-in silico-based testing strategy is developed using the isoflavone daidzein and its gut microbial metabolite S-equol as model compounds.

METHODS AND RESULTS

Anaerobic rat fecal incubations are optimized and performed to derive the apparent maximum velocities (Vmax ) and Michaelis-Menten constants (Km ) for gut microbial conversion of daidzein to dihydrodaidzein, S-equol, and O-desmethylangolensin, which are input as parameters for a physiologically based kinetic (PBK) model. The inclusion of gut microbiota in the PBK model allows prediction of S-equol concentrations and slightly reduced predicted maximal daidzein concentrations from 2.19 to 2.16 µm. The resulting predicted concentrations of daidzein and S-equol are comparable to in vivo concentrations reported.

CONCLUSION

The optimized in vitro approach to quantify kinetics for gut microbial conversions, and the newly developed PBK model for rats that includes gut microbial metabolism, provide a unique tool to predict the in vivo consequences of daidzein microbial metabolism for systemic exposure of the host to daidzein and its metabolite S-equol. The predictions reveal a dominant role for daidzein in ERα-mediated estrogenicity despite the higher estrogenic potency of its microbial metabolite S-equol.

Dietary daidzein decreases food intake accompanied with delayed gastric emptying in ovariectomized rats

We previously found that equol, a metabolite of intestinal bacterial conversion from soy isoflavone daidzein, has female-specific anorectic effects. In the present study, we used seven-week-old female ovariectomized (OVX) Sprague Dawley rats to test the hypothesis that the anorectic effect of dietary daidzein may be attributed to delayed gastric emptying. Results suggest that dietary daidzein delays gastric emptying and that it has an anorectic effect with residual gastric contents, but not without gastric contents. Dietary equol significantly decreased daily food intake in the OVX rats without sleeve gastrectomy, but not in those with sleeve gastrectomy, suggesting that the accumulation of food in the stomach is required for the anorectic effect of equol to occur. These results support the hypothesis that the anorectic effect of dietary daidzein is attributed to delayed gastric emptying.

Dietary daidzein induces accumulation of S-equol in enterohepatic circulation to far higher levels than that of daidzein in female rats with and without ovariectomy

We previously found that daidzein decreased food intake in female rats. To understand the mechanism of anorectic action of dietary daidzein, it is necessary to determine distributions of daidzein and S-equol, a metabolite of intestinal bacterial conversion from daidzein, in the body. In the present study, we measured the concentrations of daidzein and S-equol in serum and bile in sham-operated and ovariectomized female rats fed a diet containing 150 mg/kg daidzein for 7 days. Dietary daidzein increased serum and bile concentrations of S-equol to far higher levels than those of daidzein. S-equol concentration was more than several hundred fold-higher in bile than in serum, regardless of ovariectomy. Moreover, to investigate whether accumulation of S-equol is facilitated by efficient enterohepatic circulation during continuous intake of daidzein and S-equol, female rats were fed diet containing daidzein or S-equol (both 150 mg/kg), or control diet for 1, 2, 3, or 5 days. Dietary daidzein significantly increased serum and bile concentrations of S-equol in a time-dependent manner, but not those of daidzein. These results indicated that substantial proportion of dietary daidzein was converted to S-equol, which underwent efficient enterohepatic circulation and predominantly accumulated there.

The daidzein- and estradiol- induced anorectic action in CCK or leptin receptor deficiency rats

We investigated the effect of daidzein feeding and estradiol treatment on food intake in cholecystokinin-1 receptor (CCK1R) deficiency, leptin receptor (ObRb) deficiency rats and their wild-type rats. These rats underwent an ovariectomy or a sham operation. For the 5 week experiment, each rat was divided in three groups: control, daidzein (150 mg/kg diet), and estradiol (4.2 μg/rat/day) groups. In both CCK1R+ and CCK1R− rats, daidzein feeding and estradiol treatment significantly decreased food intake. Daidzein feeding significantly reduced food intake in ovariectomized ObRb− rats, although not in ObRb+ rats. Estradiol treatment significantly lowered food intake in ovariectomized ObRb+ and ObRb− rats. In the ovariectomized rats, estradiol treatment significantly increases uterine weight, while daidzein feeding did not change it, suggesting that daidzein might have no or weak estrogenic effect in our experiment. These results suggest that CCK1R and ObRb signalings were not essential for the daidzein- and estradiol-induced anorectic action.

Dynamics of appetite-mediated gene expression in daidzein-fed female rats in the meal-feeding method

We previously found that daidzein decreased food intake in female rats. The present study aimed to elucidate the relationship between dynamics of appetite-mediated neuropeptides and the anorectic effect of daidzein. We examined appetite-mediated gene expression in the hypothalamus and small intestine during the 3 meals per day feeding method. Daidzein had an anorectic effect specifically at the second feeding. Neuropeptide-Y (NPY) and galanin mRNA levels in the hypothalamus were significantly higher after feeding in the control but not in the daidzein group, suggesting that daidzein attenuated the postprandial increase in NPY and galanin expression. The daidzein group had higher corticotrophin-releasing hormone (CRH) mRNA levels in the hypothalamus after feeding, and increased cholelcystokinin (CCK) mRNA levels in the small intestine, suggesting that CCK is involved in the hypothalamic regulation of this　anorectic effect. Therefore, daidzein may induce anorexia by suppressing expression of NPY and galanin and increasing expression of CRH in the hypothalamus.

Improvement of the circulatory function partially accounts for the neuroprotective action of the phytoestrogen genistein in experimental ischemic stroke

We tested the hypothesis that the phytoestrogen genistein protects the brain against ischemic stroke by improving the circulatory function in terms of reduced production of thromboxane A2 and leukocyte-platelet aggregates, and of preserved vascular reactivity. Ischemia-reperfusion (90 min-3 days, intraluminal filament) was induced in male Wistar rats, and functional score and cerebral infarct volume were the end points examined. Genistein (10mg/kg/day) or vehicle (β-cyclodextrin) was administered at 30 min after ischemia or sham-operation. Production of thromboxane A2 and leukocyte-platelet aggregates, as well as reactivity of carotid artery to U-46619 (thromboxane A2 analogue) and to platelet releasate was measured. At 3 days post-ischemia, both improvement in the functional examination and reduction in the total infarct volume were shown in the ischemic genistein-treated group. Genistein significantly reverted both the increased thromboxane A2 concentration and the increased leukocyte-platelet aggregates production found in samples from the ischemic vehicle-treated group. Both U-46619 and platelet releasate elicited contractions of the carotid artery, which were significantly lower in the ischemic vehicle-treated group. Genistein significantly restored both the decreased U-46619- and the decreased platelet releasate-elicited contractile responses. In conclusion, genistein protects the brain against an ischemia-reperfusion challenge, at least in part, by its beneficial effects on the circulatory function.

Proliferative and estrogenic sensitivity of the mammary gland are modulated by isoflavones during distinct periods of adolescence

Isoflavone (ISO) exposure during adolescence has been demonstrated to modulate the estrogenic and proliferative sensitivity of the adult breast tissue. In this study, we investigated whether ISO exposure restricted to the period of puberty is sufficient to result in similar effects. Female rats were divided into three groups receiving either lifelong an ISO-free diet (IDD) or an ISO-rich diet (ISD), or an ISD from postnatal day (PND) 30 to PND 60 covering the time period of puberty (pISD). Serum concentrations of ISO and metabolites were determined at PND 50 and 80. At PND 50, ISD animals had significant higher equol serum levels than pISD animals. Onset of puberty occurred significantly earlier in the pISD and ISD group compared to the animals fed IDD. Cycle length was shortest in pISD group. To determine estrogen sensitivity of the adult breast tissue, adult rats were ovariectomized and subcutaneously treated either with estradiol (E(2)) or with genistein (GEN) for 3 days (PND 77-80). Analysis of Ki-67 and proliferating cell nuclear antigen (PCNA) expression showed a reduced proliferative response of the breast to E(2) in pISD and ISD animals compared to IDD group, while the induction of progesterone receptor (PR) was higher in both IDD and pISD compared to ISD fed rats. Our results demonstrate that ISO exposure during puberty is sufficient to reduce the proliferative response of the adult mammary gland but not to reduce the response of classical E(2) sensitive genes like the PR. In summary, our results demonstrate that animals exposed during different periods of their adolescence to ISO differ in several physiological aspects. In addition, the detected differences in the serum equol levels between pISD and ISD rats and the detected differences in the estrogen sensitivity of the breast clearly underline this assumption.

Analysis of daidzein in nanoparticles after oral co-administration with sodium caprate to rats by ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry

An ultra-performance-liquid-chromatography-quadrupole-time-of-flight mass spectrometry (UPLC/Q-TOF-MS) method was developed and validated for the quantitation of daidzein (DZ) in rat plasma. Ethylparaben was chosen as internal standards (IS). DZ was linear over the range of 0.001-5 μg/mL. The lower limit of quantification (LLOQ) was 0.001 μg/mL and the limit of detection (LOD) was 0.0005 μg/mL. The intra-day and inter-day relative standard deviations (RSDs) were ranged from 3.59% to 6.43% and 5.35% to 7.25%, respectively. This UPLC/Q-TOF-MS method provided good specifity, highly sensitivity, accurate and high-speed detection (6 min), applicable to the pharmacokinetics study in rats in vivo after oral administration of free daidzein solution, daidzein-loaded poly (lactide-co-glycolide) (PLGA) nanoparticles (D-NPs) suspension and D-NPs co-administered with sodium caprate (C(10)) which as the oral absorption promoter. It was shown that the pharmacokinetics behavior was significantly improved after the oral administration of D-NPs suspension co-administered with absorption promoter C(10) by the fact that the relative bioavailability were enhanced about 4.24-fold, compared to that of DZ suspension.

Chemoprotective activity of the isoflavones, genistein and daidzein on mutagenicity induced by direct and indirect mutagens in cultured HTC cells

Isoflavones are phenolic compounds widely distributed in plants and found in a high percentage in soybeans. They have important biological properties and are regarded as potential chemopreventive agents. The aim of this study was to verify the preventive effect of two soy isoflavones (genistein and daidzein) by a micronucleus assay, analysis of GST activity, and real-time RT-PCR analysis of GSTa2 gene expression. Mutagens of direct (doxorubicin) and indirect (2-aminoanthracene) DNA damage were used. Hepatoma cells (HTC) were treated with genistein or daidzein for 26 h at noncytotoxic concentrations; 10 μM when alone, and 0.1, 1.0 and 10 μM when combined with genotoxic agents. The micronucleus test demonstrated that both isoflavones alone had no genotoxic effect. Genistein showed antimutagenic effects at 10 μM with both direct and indirect DNA damage agents. On phase II enzyme regulation, the current study indicated an increase in total cytoplasmic GST activity in response to genistein and daidzein at 10 μM supplementation. However, the mRNA levels of GSTa2 isozymes were not differentially modulated by genistein or daidzein. The results point to an in vitro antimutagenic activity of genistein against direct and indirect DNA damage-induced mutagenicity.

Evaluation of daidzein-loaded chitosan microspheres in vivo after intramuscular injection in rats

Daidzein-loaded chitosan microspheres were prepared by emulsification/chemical-crosslinking technique. The dialysis bag method determined the release of daidzein from the microspheres. It demonstrated that the accumulative release curve in vitro was fit for the zero-order release equation and had good correlation with the absorptive fraction in vivo, suggesting the dialysis bag method evaluated the release of the microspheres well. The release of chitosan determined by the ninhydrin assay in vitro was very slow, less than 3 percent at 35 day. The pathological section by hematoxylin-eosin staining found the good biocompatibility of the prepared microspheres in the injective site. Combining the degradation photos by scanning electron microscopy with the plasma concentration-time data, it was speculated that the drug on the surface of the microspheres firstly released, then the major of drug near the surface and the inner of the microspheres released by diffusion through the shallow cavities and crack, lastly the drug released rapidly and completely being companied with the beginning of polymer degradation.

The comparison of different daidzein-PLGA nanoparticles in increasing its oral bioavailability

The aim of this research was to increase the oral bioavailability of daidzein by the formulations of poly(lactic-co-glycolic) acid (PLGA) nanoparticles loaded with daidzein. Amongst the various traditional and novel techniques of preparing daidzein-loaded PLGA nanoparticles, daidzein-loaded phospholipid complexes PLGA nanoparticles and daidzein-loaded cyclodextrin inclusion complexes PLGA nanoparticles were selected. The average drug entrapment efficiency, particle size, and zeta potential of daidzein-loaded phospholipid complexes PLGA nanoparticles and daidzein-loaded cyclodextrin inclusion complexes PLGA nanoparticles were 81.9% ± 5%, 309.2 ± 14.0 nm, -32.14 ± 2.53 mV and 83.2% ± 7.2%, 323.2 ± 4.8 nm, -18.73 ± 1.68 mV, respectively. The morphological characterization of nanoparticles was observed with scanning electron microscopy by stereological method and the physicochemical state of nanoparticles was valued by differential scanning calorimetry. The in vitro drug-release profile of both nanoparticle formulations fitted the Weibull dynamic equation. Pharmacokinetic studies demonstrated that after oral administration of daidzein-loaded phospholipid complexes PLGA nanoparticles and daidzein-loaded cyclodextrin inclusion complexes PLGA nanoparticles to rats at a dose of 10 mg/kg, relative bioavailability was enhanced about 5.57- and 8.85-fold, respectively, compared to daidzein suspension as control. These results describe an effective strategy for oral delivery of daidzein-loaded PLGA nanoparticles and might provide a fresh approach to enhancing the bioavailability of drugs with poor lipophilic and poor hydrophilic properties.

Enhanced intestinal absorption of daidzein by borneol/menthol eutectic mixture and microemulsion

In the present study, the effect of a borneol/menthol eutectic mixture (25:75) and microemulsion on the absorption of daidzein in rat intestinal membrane was evaluated. The microemulsion formulation was composed of ethyl oleate (oil), Cremophor RH40 (surfactant), PEG400 (co-surfactant), and water. The borneol/menthol eutectic mixture and its microemulsion were found to enhance the intestinal absorption of daidzein in vitro. A diffusion chamber system with isolated rat intestinal membranes was used. In contrast, verapamil (0.3 mM), a typical P-glycoprotein inhibitor, showed no effect on the absorption of daidzein by this system. A pharmacokinetic study was conducted in rats. After oral administration of daidzein at a dose of 10 mg/kg in the form of either borneol/menthol eutectic mixtures or suspension, the relative bioavailability of borneol/menthol eutectic mixtures and microemulsion was enhanced by about 1.5- and 3.65-fold, respectively, compared with a daidzein suspension. In conclusion, a borneol/menthol eutectic mixture can enhance the absorption of daidzein, although the mechanism of absorption enhancement is still unclear.

Risks and benefits of dietary isoflavones for cancer

A high intake of fruits and vegetables is associated with a lower risk of cancer. In this context, considerable attention is paid to Asian populations who consume high amounts of soy and soy-derived isoflavones, and have a lower risk for several cancer types such as breast and prostate cancers than populations in Western countries. Hence, interest focuses on soyfoods, soy products, and soy ingredients such as isoflavones with regard to their possible beneficial effects that were observed in numerous experiments and studies. The outcomes of the studies are not always conclusive, are often contradictory depending on the experimental conditions, and are, therefore, difficult to interpret. Isoflavone research revealed not only beneficial but also adverse effects, for instance, on the reproductive system. This is also the case with tumor-promoting effects on, for example, breast tissue. Isoflavone extracts and supplements are often used for the treatment of menopausal symptoms and for the prevention of age-associated conditions such as cardiovascular diseases and osteoporosis in postmenopausal women. In relation to this, questions about the effectiveness and safety of isoflavones have to be clarified. Moreover, there are concerns about the maternal consumption of isoflavones due to the development of leukemia in infants. In contrast, men may benefit from the intake of isoflavones with regard to reducing the risk of prostate cancer. Therefore, this review examines the risks but also the benefits of isoflavones with regard to various kinds of cancer, which can be derived from animal and human studies as well as from in vitro experiments.

Endocrine milieu and erectile dysfunction: is oestradiol-testosterone imbalance, a risk factor in the elderly?

Oestrogens are not exclusive to the female gender but occur in moderate circulating levels of 25-70 pg ml⁻¹ in men, compared to 44-153 pg ml⁻¹ in women. Arising from aromatisation of testosterone (T), oestrogen is considered to have many opposing physiological functions and the progressive T decline in the aging male is associated with relative and/or absolute increase in serum oestradiol (E₂). Sexual disinterest and erectile dysfunction (ED) in the elderly may well be due to pathophysiological E₂-T imbalance; the altered hormonal ratio may also explain the higher incidence of ED in hyperestrogenism or following exposure to environmental/plant oestrogens.

Urinary isoflavone phytoestrogens in German children and adolescents--a longitudinal examination in the DONALD cohort

SCOPE

In light of concerns about hormonally active agents, it is important to assess human exposure to such compounds, especially in children as a susceptible subgroup. Estrogenic plant constituents are present in the human diet in varying levels, in particular the isoflavones daidzein (DAI) and genistein (GEN). We aimed to examine age-dependent and secular trends in phytoestrogen exposures and to investigate equol (EQ) excretion of German children using biomarker analysis in 24-h urine samples from a longitudinally designed study.

METHODS AND RESULTS

The concentrations of DAI, its metabolite EQ and GEN were determined by GC-MS analysis in 24-h urines (510 samples) collected between 1985 and 2000 in 90 (47 boys) German children (6-18 years old), who are participants in the Dortmund Nutritional and Anthropometric Longitudinally Designed study. The results from the urinary biomarker analysis indicate isoflavone exposures at quite variable levels in German children: Analyte concentrations in over 500 urine samples cover the range reported previously in adults on typical German diet and with soy intake. EQ, the DAI metabolite produced by the gastrointestinal microflora, was detected in a high fraction of all samples, with 28/90 children (31%) excreting EQ in all their urines, and 62/90 children (68%) in at least one sample. Interestingly, when multiple urines obtained from individuals at different ages (6-18 years) were analyzed, EQ formation did not appear to be a constant trait over time. When stratified by sex, DAI, EQ and GEN concentrations (ng/mL) in urines and excretion rates (μg/day) were similar in boys and girls. Total isoflavone excretion rates (μg/day) increased during childhood (6-12 years) (p=0.02) and were constant during adolescence (13-18 years) (p=0.6). No clear trend for changes in dietary isoflavone exposure over the total study period was seen (p=0.7).

CONCLUSIONS

In conclusion, biomarkers in urine of German children and adolescents indicate a frequent, but widely variable dietary isoflavone intake and suggest no secular increase (1985-2000) in the exposure to isoflavone phytoestrogens among German children and adolescents.

Modulation of monoamine neurotransmitters in fighting fish Betta splendens exposed to waterborne phytoestrogens

Endogenous estrogens are known to affect the activity of monoamine neurotransmitters in vertebrate animals, but the effects of exogenous estrogens on neurotransmitters are relatively poorly understood. We exposed sexually mature male fighting fish Betta splendens to environmentally relevant and pharmacological doses of three phytoestrogens that are potential endocrine disruptors in wild fish populations: genistein, equol, and β-sitosterol. We also exposed fish to two doses of the endogenous estrogen 17β-estradiol, which we selected as a positive control because phytoestrogens are putative estrogen mimics. Our results were variable, but the effects were generally modest. Genistein increased dopamine levels in the forebrains of B. splendens at both environmentally relevant and pharmacological doses. The environmentally relevant dose of equol increased dopamine levels in B. splendens forebrains, and the pharmacological dose decreased norepinephrine (forebrain), dopamine (hindbrain), and serotonin (forebrain) levels. The environmentally relevant dose of β-sitosterol decreased norepinephrine and dopamine in the forebrain and hindbrain, respectively. Our results suggest that sources of environmental phytoestrogens, such as runoff or effluent from agricultural fields, wood pulp mills, and sewage treatment plants, have the potential to modulate neurotransmitter activity in free-living fishes in a way that could interfere with normal behavioral processes.

Responses of estrogen sensitive tissues in female Wistar rats to pre- and postnatal isoflavone exposure

Effects of isoflavones on estrogen sensitive tissues are discussed controversially. This study was designed to investigate tissue specific effects of an isoflavone exposure through different periods of life in female Wistar rats and to compare the effects of genistein (GEN) to those of mixed dietary isoflavones, GEN and daidzein (DAI). One group received an isoflavone-free diet (IDD), another was fed an isoflavone-rich diet (IRD) and the third group an IDD supplemented with GEN (GEN(d)) prior to mating, throughout pregnancy and up to weaning. The offspring were kept on the respective diets during growth, puberty and adulthood. The weight of the uterus, the height of the uterine and vaginal epithelium, the bone mineral density of the tibia, and the expression of the estrogen sensitive gene CaBP9K in the liver were determined. At d21, the uterine weight, the uterine epithelium and the expression of CaBP9K in the liver were significantly stimulated in GEN(d) animals compared to IDD and IRD. Interestingly, bone mineral density was increased in GEN(d) and in IRD animals. Around puberty (d50) neither uterine wet weights nor trabecular bone density differed significantly among the isoflavone groups and the IDD control. At d80 no significant differences in uterine weight were observed among IDD, GEN(d) and IRD animals. However, bone mineral density was increased in GEN(d) and IRD animals. In summary, our results demonstrate that lifelong dietary exposure to isoflavones can affect estrogen sensitive tissues, apparently in a tissue selective manner. With respect to health risk and benefit our data indicate that an increased bone mineral density can be achieved by lifelong exposure to an IRD, which, in contrast to GEN supplementation, does not seem to stimulate the proliferation of the uterine epithelium.

In vivo metabolic tracking of 14C-radiolabelled isoflavones in kudzu (Pueraria lobata) and red clover (Trifolium pratense) extracts

Absorption, distribution and elimination of 14C-labelled isoflavone-containing extracts from kudzu (Pueraria lobata) root culture and red clover (Trifolium pratense) cell culture were investigated in an in vivo rat model. The predominant isoflavones in the kudzu extract were the glycosides puerarin, daidzin and malonyl daidzin, while in the red clover extract, the major isoflavones were formononetin and its derivatives, genistein and biochanin A, with radioactivities of 3.770 and 7.256 MBq/g, respectively. Male Sprague-Dawley rats, implanted with a jugular catheter and a subcutaneous ultrafiltrate probe, were orally administered with 14C-labelled isoflavone extracts from either kudzu or clover cell cultures. Serum, interstitial fluid (ISF), urine and faeces were collected using a Culex Automated Blood Collection System for 24 h. Analysis of bone tissues revealed that radiolabel accumulated in the femur, tibia and vertebrae at 0.04, 0.03 and 0.01 % of the administered dose, respectively, in both kudzu and red clover treatments. The liver accumulated the greatest concentration of radiolabel among the tissues tested, at 1.99 and 1.54 % of the administered kudzu and red clover extracts, respectively. Serum and ISF analysis showed that both extracts were rapidly absorbed, distributed in various tissues, and largely eliminated in the urine and faeces. Urine and faeces contained 8.53 and 9.06 % of the kudzu dose, respectively, and 3.60 and 5.64 % of the red clover dose, respectively. Serum pharmacokinetics suggest that extracts from kudzu may undergo enterohepatic circulation.

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

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

Dietary soy isoflavone-aglycone lowers food intake in female rats with and without ovariectomy

OBJECTIVE

Estrogens downregulate eating behavior, and soy isoflavones are known to be estrogenic agents. We aimed to examine whether the estrogenic property of soy isoflavones can affect food intake and body weight.

METHODS AND PROCEDURES

Seven-week-old male, female, and ovariectomized (OVX) Sprague-Dawley rats were given free access to a diet containing 100-300 mg total isoflavone/kg diet, or to a control diet, either with or without concurrent administration of estradiol by subcutaneous implantation.

RESULTS

Dietary soy isoflavone was shown to lower food intake in female rats, whether or not the animals had undergone ovariectomy. Administration of estradiol lowered the food intake in male rats and in OVX female rats. The decrease in weekly food intake in female rats led to a reduction in their weekly gain in body weight. Dietary soy isoflavone significantly increased the concentration of serum isoflavones, especially equol (a metabolite of daidzein), regardless of gender or ovariectomy. Dietary soy isoflavone did not affect either serum estradiol concentration or uterine and didymus weights, but estradiol administration improved the uterine atrophy in OVX rats, and decreased the didymus weight in male rats.

DISCUSSION

Soy isoflavone lowers the food intake in female rats, but not in the male animals. Contrary to the hypothesis currently in vogue, the reduction in food intake caused by soy isoflavone may not be a purely estrogenic effect. This follows from the finding that the effects of soy isoflavones on food intake and on the reproductive organs differ from the corresponding effects produced by estrogen.

Simultaneous determination of daidzein, equol, genistein and bisphenol A in human urine by a fast and simple method using SPE and GC-MS

Human diet contains weakly estrogenic compounds such as daidzein (DAI) and genistein (GEN), phytoestrogens present in soy and many vegetables as well as bisphenol A (BPA), a contaminant from packing materials and plastic containers for foods and beverages. In light of concerns about hormonally active agents, biomonitoring methods are needed to assess human exposure to such compounds. A method for simultaneous determination of DAI, its metabolite equol (EQ), GEN, and BPA by GC-MS analysis was established, validated and applied to measure concentrations in human urine. Sample preparation involves enzymatic conjugate cleavage, SPE and derivatization by silylation. For GC/MS analysis, deuterated DAI and GEN and( 13)C-BPA are used as internal standards. LOD are 4, 4, 5 and 3 ng/mL urine for DAI, EQ, GEN and BPA, respectively. Interassay variations were 9% for DAI, 15% for EQ, 18% for GEN and 10% for BPA. Simple workup and accuracy of the method are suited for biomonitoring. An analysis of urine samples from 15 adults consuming typical German food revealed dietary exposure to phytoestrogens in all samples: GEN concentrations ranged between 13 and 238 ng/mL, those for DAI ranged from 12 to 356 ng/mL. More than half of the individuals excreted also the more estrogenic metabolite EQ, at levels of 8-128 ng/mL. Higher concentrations (GEN: 820, DAI: 960 and EQ: 1740 ng/mL) were measured in a 24 h urine sample upon ingestion of soy protein (50 g with 12.9 mg DAI and 25.2 mg GEN). Only urine collected after some days on strict phytoestrogen-free diet had undetectable isoflavone levels. BPA was detected in 9 of 15 urine samples ranging from 3 to 11 ng/mL, and at 55 ng/mL in one sample. In conclusion, a reliable method to determine BPA and isoflavones in urine was established and applied in a pilot study: Biomonitoring results show much higher dietary exposure to phytoestrogens than to BPA in German adults.

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

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

Toxicokinetics of bisphenol A in pregnant DA/Han rats after single i.v. application

Bisphenol A (BPA) is an important chemical in the production of epoxy resins and polycarbonate plastics, and basic monomers which are used for a variety of applications. Consumer exposure to BPA may be possible from migration of BPA from dental sealants or from polycarbonate or epoxy-lined food and drink containers. BPA is known to act as weak estrogen mimic in rodents, and there is a concern of adverse endocrine effects, especially from prenatal exposure to this potential 'endocrine disruptor'. To address this concern, we have studied the disposition and transplacental transfer of BPA in pregnant DA/Han rats on day 18 of gestation. The BPA concentrations were determined by GC/MS analysis in maternal blood, maternal organs (liver, kidney, uterus), placenta and fetuses (fetal liver and residual tissues) at different time-points (5-360 min) after intravenous administration of 10 mg BPA/kg body weight. Total BPA (aglycone and conjugates) was analyzed in all tissue samples after enzymatic hydrolysis and liquid/liquid extraction; in maternal plasma, total BPA and BPA aglycone were analyzed in parallel samples (with/without hydrolysis). Soon (5 min) after the i.v. injection a mean total BPA concentration of 3.8 microg/ml was found in maternal plasma; it declined in the first 2 h to 0.7 microg/ml. Early after injection, the majority of circulating BPA (almost 80%) was still in the aglycone form, but, metabolism by phase II enzymes decreased the BPA aglycone concentration to 0.3 microg/ml after 2 h. Despite this efficient conjugation, BPA was rapidly distributed in the organism: In well perfused organs peak concentrations for total BPA were attained 20-30 min after intravenous administration, with mean values of about 9.7 microg/g in maternal liver, 8.6 microg/g in kidneys, and 6.2 microg/g in the uterus. The peak values in other tissues were lower, with 4.0 microg/g for placenta, 3.3 microg/g for fetal liver, and 2.4 microg/g for residual fetus homogenate. The BPA levels in all tissues thereafter declined more or less in parallel with those in maternal blood. The rather similar concentration time course in placenta and fetal liver indicates that BPA is readily transferred across the placenta of DA/Han rats to the fetus. Our data on BPA disposition in DA/Han rats are discussed in the context of other kinetic studies with BPA in pregnant rats, and in relation to the previous results from our laboratory (Degen et al. Arch Toxicol 76:23-29, 2002a, b, c) demonstrating comparable transplacental transfer of daidzein, a phytoestrogen that accounts for a significant portion of total human exposure to potential endocrine disruptors.

Soy isoflavones and bone health: a double-edged sword?

Numerous publications and research studies on isoflavones have prompted a nationwide increase in the consumption of soy-based foods and supplements in the United States. Isoflavones are natural endocrine active compounds generally considered to promote health and prevent or slow the onset of certain chronic diseases such as osteoporosis. The beneficial effects of soy isoflavones on bone may, however, be life-stage specific and dependent on the estrogen receptor number and endogenous hormone milieu. Perimenopausal and early menopausal women may therefore be more receptive to the therapeutic effects of isoflavones on bone loss prior to the diminution of estrogen receptors that occurs in the postmenopausal years, whereas laboratory studies in developmental age range animals have demonstrated the potential for adverse effects following exposure to high levels of soy isoflavones. Clinical studies in developing humans that either support or refute findings in animal studies are lacking. The effects of chronic consumption of high levels of soy isoflavones at each life stage to assess risk-benefit ratios should be a high priority of research.

Estrogenic and genotoxic potential of equol and two hydroxylated metabolites of Daidzein in cultured human Ishikawa cells

The soy isoflavone daidzein (DAI) is known to undergo metabolism to equol (EQO) and to 3'-hydroxy-DAI (3'-HO-DAI) and 6-hydroxy-DAI (6-HO-DAI) in humans. In order to better understand the implications of soy diets for human health, the hormonal and genotoxic activities of these DAI metabolites were studied in cultured human endometrial carcinoma cells. When the estrogenicity was tested by cell-free binding to recombinant human estrogen receptor (ER) alpha and beta as well as by the induction of enzyme activity and gene expression of alkaline phosphatase (ALP) in Ishikawa cells, the ranking order was EQO>DAI>3'-HO-DAI>6-HO-DAI. All compounds had a higher affinity to ERbeta than to ERalpha. No significant anti-estrogenic effects of the DAI metabolites were observed in the cells at non-cytotoxic concentrations. The in vitro genotoxicity was assessed by analyzing effects on cell cycle distribution and cell morphology as well as the induction of micronuclei (MN). EQO caused a slight increase in G1 and decrease in S phase of the cell cycle, and slightly but significantly induced kinetochore-positive as well as kinetochore-negative MN and an elevated proportion of abnormal mitotic spindles. 3'-HO-DAI, but not 6-HO-DAI, induced kinetochore-negative MN. The observation that major human metabolites of DAI exhibit estrogenic and genotoxic potential may be of relevance for the safety evaluation of diets containing soy isoflavones.

Kudzu Root Extract Suppresses Voluntary Alcohol Intake and Alcohol Withdrawal Symptoms in P Rats Receiving Free Access to Water and Alcohol

Alcohol-preferring (P) rats, given free choice to drink water or 15% alcohol, drank 7-10 g of alcohol/kg/day, giving blood alcohol values ranging from 16 to 24 mg/dL. Body weight and food and total fluid intake values in control and alcohol-drinking P rats did not differ significantly, while water intake was inversely related to the amount of alcohol consumed. Alcohol withdrawal after 50 days of alcohol drinking caused withdrawal symptoms such as hypersensitivity, poor landing coordination, and tremors. A daily 0.5, 0.75, and 1.0 g/kg dose of kudzu root (KdR) did not affect body weight and food and water intake values in control (no alcohol) P rats. Subchronic feeding of relatively higher KdR doses (0.75 and 1.0 g/kg) caused a 25-30% reduction in weight gain. The 0.5 g/kg KdR dose caused a 50-60% reduction in alcohol consumption, abolished the development of alcohol withdrawal symptoms, but did not affect blood alcohol levels. The higher KdR doses did not further reduce alcohol consumption. Alcohol suppressed the weight-reducing effects of KdR. The KdR extract used in this study contained 150 mg/g of puerarin, 13 mg/g of daidzin, 4 mg/g of daidzein, 3 mg/g of genistin, 0.2 mg/g of genistein, and 1 mg/g of glycetin. Blood and liver samples contained mostly puerarin and a trace amount of daidzein that may have been formed by the hydrolysis of daidzin by liver enzymes. An important observation was that brain samples obtained from KdR-fed or alcohol + KdR-fed rats did not contain any of the KdR isoflavones. Thus, KdR isoflavones suppressed alcohol drinking and withdrawal symptoms without entering the brain.

Inhibition of reactive nitrogen species effects in vitro and in vivo by isoflavones and soy-based food extracts

Recent studies have shown that soy isoflavone inhibits inducible nitric oxide (NO) synthase activities and is reported to have peroxynitrite scavenging ability. Consequently, we investigated whether isoflavones (daidzein and genistein) and extracts from soy-based products (miso, soymilk, tofu, soy sprout, black soybean, soybean, and yuba) would inhibit the reactive nitrogen species (RNS) effect in vitro and in vivo. In the in vitro experiments [including the protection of cellular DNA from peroxynitrite or sodium nitroprusside damage, an inhibitory effect on nitric oxide production from lipopolysaccharide (LPS)-induced RAW 264.7 cells, and nitric oxide scavenging ability], extracts from soy-based foods showed a potent antioxidant activity and an inhibiting effect on RNS activity. These effects were correlated with total isoflavone content. In the in vivo experiments, rats were given isoflavones (4.0 mg/kg bw) or soy-based product extracts (1.0 g/kg bw) orally for 1 week and were injected with vehicle H(2)O (1 mL/kg bw) or LPS (10 mg/kg bw) on the day 7. Twelve hours after treatment, the rats were killed, and blood serum was collected for analysis. The intraperitoneal administration of LPS resulted in an increase in serum nitrite, nitrate, and nitrotyrosine concentrations. These are stable metabolite end products of nitric oxide, to 4-, 16-, and 5-fold levels, (4, 10 microM and 58 +/- 14 pmol/mL), of the placebo control, respectively. Results showed that oral administration of isoflavones and extracts from soy-based products significantly decreased serum nitrite, nitrate, and nitrotyrosine levels in LPS-induced rats. This study demonstrates that soy isoflavone supplementation may inhibit RNS-induced oxidation both in vitro and in vivo.

Estrogenic isoflavones in rodent diets

Many rodent diets contain components such as soy isoflavones (daidzein and genistein) known to have estrogenic properties. The dietary background of phytoestrogens may modulate some responses to environmental estrogens when these compounds are tested in rodent bioassays. Thus, and since only few data were available on the phytoestrogen content of rodent diets commonly used in European laboratories, it was of interest to analyze the daidzein and genistein contents of our standard animal feeds. Isoflavone contents were determined in seven batches of rodent chow (from two suppliers in Germany, Altromin and Ssniff) by high-performance liquid chromatography, and also analyzed in six rodent diets from the United States. The soy-based rodent diets from Germany contained isoflavone (daidzein plus genistein) concentrations in the range of 0.3-0.55 mg/g feed. These isoflavone contents are similar to those analyzed in the US rodent diets, and similar to values reported by others, including one particular lot of feed (with 0.35 mg isoflavones per g) which produced a large uterotrophic response in immature ovariectomized rats [Environ. Health Perspect., 106 (1998) 369]. Coumestrol was found in a sample of commercial rabbit food at rather high levels (0.27 mg/g), but, this phytoestrogen was not detected (<1 microg/g feed) in any of the other samples we analyzed. The soy components in our rodent diet produce a measurable background of daidzein and genistein in blood of female DA/Han rats, total isoflavones (aglycone plus conjugates) ranging between 90 and 290 ng/ml plasma. The ovariectomized animals kept on this chow, showed no signs of estrogenization of the reproductive tract (uterus, vagina), and responded normally to (xeno-)estrogen administration in a uterotrophic assay [J. Steroid Biochem. Mol. Biol., 73 (2000) 1]. Moreover, ovariectomized Wistar rats on our standard rodent diet (Ssniff R/M H) had lower uterine weights than animals kept on the isoflavone-free (solvent extracted) chow; both groups of rats responded to genistein administration with an increase in uterine weights. These results suggest that--albeit the sensitivity of the rodent uterotrophic assay is not reduced by the use of a diet containing soy isoflavones at commonly encountered levels--attention should be given to a variable dietary phytoestrogen background.

Integration of mechanistic data in the toxicological evaluation of endocrine modulators

Controversy has arisen concerning the likelihood of adverse health effects due to exposure to hormonally active agents or endocrine modulators such as environmental estrogens. With the aim to improve the basis for their toxicological evaluation, several chemicals of anthropogenic (bisphenol A, octylphenol, o,p'-DDT) and of natural origin (daidzein, genistein) were investigated with regard to their mode of hormonal action and potency as well as toxicokinetics. Experimental toxicodynamic and toxicokinetic data illustrate important points in a comparative assessment of environmental estrogens. A novel concept, the Hygiene-Based Margine of Safety (HBMOS), has been suggested to characterize the relative impact of these potential endocrine modulators on human health: It integrates exposure scenarios (i.a. those generated within the European Existing Chemicals Programme) and in vivo rodent potency data for xenoestrogens and for dietary phytoestrogens. On the basis of these informations, HBMOS values calculated for the alkylphenol and bisphenol A appear sufficiently high to ensure the absence of a practical risk to human health under the present exposure conditions. For slowly accumulating compounds (e.g. DDT) with much longer half-lifes than isoflavones, such comparison should be based on comparative blood levels rather than on scenarios of daily exposures.

Chromatographic techniques for the determination of putative dietary anticancer compounds in biological fluids

Although a great number of papers demonstrate an association between high intake of fruits and vegetables and reduced risk of certain types of cancer, the epidemiological evidence is not conclusive. The identification and quantification of specific dietary anticancer compounds in plasma, urine and tissues is an important aspect of this research. We surveyed the recent literature for original papers which involved the use of separation techniques for the detection and quantification in biological fluids and tissues of putative anticancer compounds which are present in the diet. The compounds included in this review are flavonoids, phytoestrogens, carotenoids, retinoids, vitamin E and ascorbic acid. The review covers papers published in the last 3 years. For each class of compounds we discuss the sample preparation, chromatographic conditions, and validation of the methods used, in order to identify current trends in the bioanalysis of each class of these substances.