A dynamic simulation of bisphenol A dosimetry in neuroendocrine organs

Bisphenol A (BPA) is a known xenoestrogen with similar properties to 17b-estradiol. BPA and estrogen are hydrophobic compounds, and this affects the pharmacokinetics of both compounds in mammals. In a previous study we measured the distribution of BPA in female F344 rats exposed to oral doses of 0.1, 10 and 100 mg/kg. The results showed distribution to target neuroendocrine organs at all doses tested. Using these results, we developed a pharmacokinetic model to predict the dynamic uptake and excretion of BPA by various routes of exposure (po, iv, sc, ip). The model was able to simulate the entire time course (48 h) following various routes of exposure in rats over the dose ranges tested. The model indicated that the ultimate tissue uptake of BPA was established by the rapid initial transfer of free BPA into tissues. After free BPA enters the systemic circulation, metabolism and excretion reactions cause a relatively short duration and rapid decline. This period is followed by a slower long-term decline characteristic of BPA’s biphasic pharmacokinetics. Plasma protein and tissue binding reactions established the long-term half-life of BPA in the body. Route differences in tissue uptake were directly related to the competition between transfer and binding reactions during the absorption phase.

Distribution of bisphenol A in the neuroendocrine organs of female rats

The distribution of 14C-bisphenol A (BPA) in plasma and neuroendocrine organs was determined in Fischer 344 female rats following three oral doses (0.1, 10 or 100 mg/kg). Plasma and tissue maximum concentrations (Cmax) were reached within 15-30 min of dosing. Plasma areas-under-the-curve (AUC) ranged from 0.06 to 53.9 mg-h/mL. The AUCs of the pituitary gland and uterus/gonads were 16-21% higher than that of plasma. The AUCs of hypothalamus and the rest of the brain were 43.7% and 77% of the plasma AUCs, respectively. In the brain tissue, the exposure increased linearly with the oral dose, as the dose was increased from 0.1 to 10 and 100 mg/kg; the exposure in the brain relative to the plasma increased by factors of 1, 1.19 and 1.24. This indicates that the brain barrier systems do not limit the access of the lipophilic BPA to the brain. The increases of the uterus/gonads relative to the plasma were 1, 1.07 and 1.04. Tissue partitioning was also examined in vitro by the uptake of 14C-BPA. The BPA tissue/blood partition coefficients were as follows: heart, 7.5; liver, 6.1; kidney, 6.4; fat, 3.6; muscle, 2.6; breast, 3.6; ovaries, 9.1; uterus, 5.9; stomach, 5.1; and small intestine, 6.7. The tissue/cerebrospinal fluid partition coefficients were as follows: pituitary gland, 12.8; brain stem, 6.1; cerebellum, 6.4; hippocampus, 7.1; hypothalamus, 6.1; frontal cortex, 4.9; and caudate nucleus, 6.8.

Bisphenol A (BPA) pharmacokinetics with daily oral bolus or continuous exposure via silastic capsules in pregnant rhesus monkeys: Relevance for human exposures

We measured serum dBPA in non-pregnant and pregnant female rhesus monkeys, fetuses and amniotic fluid. dBPA was administered by a daily oral bolus or sc implantation of Silastic capsules; both resulted in daily average serum unconjugated dBPA concentrations of <1ng/ml. We observed lower serum concentrations of unconjugated dBPA in pregnant females relative to pre-pregnancy values, and generally lower concentrations in fetal serum than in maternal serum. Differences in pharmacokinetics of dBPA were evident between pre-pregnancy, early and late pregnancy, likely reflecting changes in maternal, fetal and placental physiology. The serum ratio of conjugated to unconjugated dBPA after continuous sc release of dBPA was similar to values reported in human biomonitoring studies and markedly lower than with oral administration, suggesting oral bolus exposure is not an appropriate human exposure model. We report elsewhere that there were numerous adverse effects on fetuses exposed to very low serum dBPA in these studies.

Effect of bisphenol A on rat metabolic profiling studied by using capillary electrophoresis time-of-flight mass spectrometry

Bisphenol A (BPA), a chemical widely used in the manufacture of polycarbonate plastics, has raised considerable concern in recent decades because of its hormone-like properties. Whether BPA exposure is a health risk remains controversial in many countries. A metabolomics study based on capillary electrophoresis time-of-flight mass spectrometry (CE-TOF/MS) was performed to study the urine metabolic profiles of Sprague-Dawley rats fed with four dose levels of BPA (0, 1, 10, and 100 μg/kg body weight) for 45 days. Multivariate pattern recognition directly reflected the metabolic perturbations caused by BPA. On the basis of univariate analysis, 42 metabolites including amino acids, polyamines, nucleosides, organic acids, carbohydrates, pterins, polyphenols, and sugar phosphates were found as the most significantly differential metabolites. The marked perturbations were related with valine, leucine and isoleucine biosynthesis, D-glutamine and D-glutamate metabolism, etc. Significant alterations of neurotransmitters (glutamate, gamma-aminobutyric acid, and noradrenaline) and neurotransmitter-related metabolites (tyrosine, histamine, valine, and taurine) suggested that the toxic effects of small-dose BPA (below 50 mg/kg/day) may contribute to its interactions with the neuromediating system. Our study demonstrated that metabolomics may offer more specific insights into the molecular changes underlying the physiological effects of BPA.

Fetal liver bisphenol A concentrations and biotransformation gene expression reveal variable exposure and altered capacity for metabolism in humans

Widespread exposure to the endocrine active compound, bisphenol A (BPA), is well documented in humans. A growing body of literature suggests adverse health outcomes associated with varying ranges of exposure to BPA. In the current study, we measured the internal dose of free BPA and conjugated BPA and evaluated gene expression of biotransformation enzymes specific for BPA metabolism in 50 first- and second-trimester human fetal liver samples. Both free BPA and conjugated BPA concentrations varied widely, with free BPA exhibiting three times higher concentrations than conjugated BPA concentrations. As compared to gender-matched adult liver controls, UDP-glucuronyltransferase, sulfotransferase, and steroid sulfatase genes exhibited reduced expression whereas β-glucuronidase mRNA expression remained unchanged in the fetal tissues. This study provides evidence that there is considerable exposure to BPA during human pregnancy and that the capacity for BPA metabolism is altered in the human fetal liver.

Interaction of zearalenone and soybean isoflavone in diets on the growth performance, organ development and serum parameters in prepubertal gilts

The aim of the present research was to determine the interactive effect of zearalenone (ZEA) and soybean isoflavone (ISO) on the growth performance, development of organs and serum parameters in prepubertal gilts. Ninety 75-day-old female pigs (Duroc × Landrace × Yorkshire, 26.5 ± 0.60 kg) were randomly allocated to nine diet treatments during the 21-day study. The experiment employed a 3 × 3 factorial design using a non-soybean meal diet with the addition of 0, 0.5 or 2.0 mg/kg ZEA and 0, 300 or 600 mg/kg ISO. The results indicated that simultaneous addition of ZEA and ISO had no significant influence on the growth performance in prepubertal gilts. Zearalenone with 2 mg/kg increased (p < 0.05) the relative weight of the reproductive organs (including uterus and vagina) but had no obvious effects (p > 0.05) on the relative weight of the heart, liver, lung, kidney and spleen. Isoflavone at 600 mg/kg could offset the increased weight of the reproductive organs induced by ZEA. Simultaneous addition of ZEA and ISO to prepubertal gilts increased the level of alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase in the serum (p < 0.05) at day 14 but their levels decreased (p < 0.05) over time. Zearalenone increased the level of malondialdehyde and decreased the concentrations of superoxide dismutase and glutathione peroxidase (p < 0.05) in the serum. The results suggested that ISO added to diets at 600 mg/kg could reduce the increase in the relative weight of reproductive organs and relieve the oxidative stress induced by ZEA added at 2 mg/kg during the growth phase in prepubertal gilts.

Serum bisphenol A pharmacokinetics and prostate neoplastic responses following oral and subcutaneous exposures in neonatal Sprague-Dawley rats

The present study examines BPA pharmacokinetics in neonatal rats following s.c. injection or oral delivery of 10 μg BPA/kg BW and compares susceptibility to estrogen-induced prostate intraepithelial neoplasia (PIN) following either exposure route. Serum BPA in PND3 rats was measured using HPLC-MS-MS. Free and total BPA at C(max) were 1.77 and 2.0 ng/ml, respectively following injection and 0.26 and 1.02 ng/ml, respectively following oral exposure. The AUC(0-2) for free and total BPA was 4.1-fold and 1.8-fold greater, respectively, in s.c. vs. oral delivery. While exposure route affected BPA metabolism, internal dosimetry following s.c. injection of 10 μg BPA/kg BW is similar to BPA levels observed in humans. Prostates from aged rats given s.c. or oral BPA neonatally and T+E implants as adults exhibited nearly identical, heightened susceptibility to PIN incidence and score as compared to neonatal oil-controls. These findings on prostate health are directly relevant to humans at current BPA exposure levels.

Estrogen receptor α and β expressions in hypothalamus-pituitary-ovary axis in rats exposed lactationally to soy isoflavones and bisphenol A

OBJECTIVES

This paper aims to investigate the uterotrophic activities of lactational exposure to combination of soy isoflavones (SIF) and bisphenol A (BPA) and to examine estrogen receptor α (ERα) and estrogen receptor β (ERβ) expressions in hypothalamus-pituitary-ovary axis and uterus.

METHODS

Maternal rats that were breeding about 8 litters were randomly divided into four groups with seven dams in each group. Dams in different treatment groups received corn oil (control), 150 mg/kg BW of SIF, 150 mg/kg BW of BPA or combination of 150 mg/kg BW of SIF and 150 mg/kg BW of BPA, respectively, from postnatal day 5 to 11 (PND5-11) by gavage. On PND12 and PND70, 10 female litters were killed and hypothalamus, pituitary, ovary and uterus were collected. ERα and ERβ expressions in these organs were detected with Western blotting assay. And vaginal opening time and estrus cycle were examined in animals fed for PND70.

RESULTS

On PND12, the relative uterine weight of rats treated with ISF or BPA or their combination was significantly higher than that of untreated rats (P<0.05). But the relative uterine weight of rats in the co-exposure group was slightly lower than that in the group only exposed to SIF or BPA. On PND 70, however, the relative uterine weight in each treatment group was not statistically different from that in the control group (P>0.05). Vaginal opening time and estrus cycle in groups treated with SIF or BPA or their combination were similar to those in the control group (P>0.05). Exposure to SIF or BPA or their combination could up-regulate or down-regulate ERα and ERβ expressions in hypothalamus, pituitary, ovary and uterus on PND12 and PND70. These regulation patterns for ERα and ERβ were different in different organs at different time points.

CONCLUSION

Lactational exposure to ISF or BPA or their combination could induce uterotrophic responses in neonate rats, which disappeared in later life. But these data fail to suggest a possibility for synergic actions between SIF and BPA. It was also demonstrated that the uterotrophic effects of SIF and BPA exposure might, at least, involve modification of ERα or ERβ expressions in the hypothalamus-pituitary-ovary axis.

The detection of dioxin- and estrogen-like pollutants in marine and freshwater fishes cultivated in Pearl River Delta, China

In this study we aimed to assess the dioxin- and estrogen-like activities of contaminants extracted from twenty species of freshwater and seawater fishes, using luciferase reporter assays. Transfected MCF7 cells were treated with sample extracts and luciferase activities were then measured at 24-h of post-treatment. The mean values of the detected dioxin- and estrogen-like activities in the freshwater fishes were 25.3 pg TEQ/g ww and 102.3 pM EEQ/g ww whereas in the seawater fishes, the values were 46.2 pg TEQ/g ww and 118.8 pM EEQ/g ww. Using sample-relevant dosage of estrogen, inductions of cell proliferation markers (i.e. retinoblastoma, cyclin D) and stimulations of cell growth were revealed by Western blotting, colony formation and BrdU uptake assays. A cotreatment with TCDD significantly reduced these effects. Using the sample extracts with different dioxin- and estrogen-like activities, similar observation was revealed. The data highlighted the mixture effect of food contaminants on human health.

Assessment of bisphenol A exposure in Korean pregnant women by physiologically based pharmacokinetic modeling

The objective of this study was to predict the exposure to bisphenol A (BPA) after oral intake in human blood and tissues using physiologically based pharmacokinetic (PBPK) modeling. A refined PBPK model was developed taking into account of glucuronidation, biliary excretion, and slow absorption of BPA in order to describe the second peak of BPA observed following oral intake. This developed model adequately described the second peak and BPA concentrations in blood and various tissues in rats after oral administration. A prospective validation study in rats additionally supported the proposed model. For extrapolation to humans, a daily oral BPA dose of 0.237 mg/70 kg/d or 0.0034 mg/kg/d was predicted to achieve an average steady-state blood concentration of 0.0055 ng/ml (median blood BPA concentration in Korean pregnant women). This dose was lower than the reference dose (RfD, 0.016 mg/kg/d) and the tolerable daily intake established by the European Commission (10 μg/kg/d). Data indicate that enterohepatic recirculation may be toxicologically important as this pathway may increase exposure and terminal half-life of BPA in humans.

Basic exploratory research versus guideline-compliant studies used for hazard evaluation and risk assessment: bisphenol A as a case study

BACKGROUND

Myers et al. [Environ Health Perspect 117:309-315 (2009)] argued that Good Laboratory Practices (GLPs) cannot be used as a criterion for selecting data for risk assessment, using bisphenol A (BPA) as a case study. They did not discuss the role(s) of guideline-compliant studies versus basic/exploratory research studies, and they criticized both GLPs and guideline-compliant studies and their roles in formal hazard evaluation and risk assessment. They also specifically criticized our published guideline-compliant dietary studies on BPA in rats and mice and 17beta-estradiol (E(2)) in mice.

OBJECTIVES

As the study director/first author of the criticized E(2) and BPA studies, I discuss the uses of basic research versus guideline-compliant studies, how testing guidelines are developed and revised, how new end points are validated, and the role of GLPs. I also provide an overview of the BPA guideline-compliant and exploratory research animal studies and describe BPA pharmacokinetics in rats and humans. I present responses to specific criticisms by Myers et al.

DISCUSSION AND CONCLUSIONS

Weight-of-evidence evaluations have consistently concluded that low-level BPA oral exposures do not adversely affect human developmental or reproductive health, and I encourage increased validation efforts for "new" end points for inclusion in guideline studies, as well as performance of robust long-term studies to follow early effects (observed in small exploratory studies) to any adverse consequences.

Predicting plasma concentrations of bisphenol A in children younger than 2 years of age after typical feeding schedules, using a physiologically based toxicokinetic model

BACKGROUND

Concerns have recently been raised regarding the safety of potential human exposure to bisphenol A (BPA), an industrial chemical found in some polycarbonate plastics and epoxy resins. Of particular interest is the exposure of young children to BPA via food stored in BPA-containing packaging.

OBJECTIVES

In this study we assessed the age dependence of the toxicokinetics of BPA and its glucuronidated metabolite, BPA-Glu, using a coupled BPA-BPA-Glu physiologically based toxicokinetic (PBTK) model.

METHODS

Using information gathered from toxicokinetic studies in adults, we built a PBTK model. We then scaled the model to children < 2 years of age based on the age dependence of physiologic parameters relevant for absorption, distribution, metabolism, and excretion.

RESULTS

We estimated the average steady-state BPA plasma concentration in newborns to be 11 times greater than that in adults when given the same weight-normalized dose. Because of the rapid development of the glucuronidation process, this ratio dropped to 2 by 3 months of age. Simulation of typical feeding exposures, as estimated by regulatory authorities, showed a 5-fold greater steady-state BPA plasma concentration in 3- and 6-month-olds compared with adults, reflecting both a reduced capacity for BPA metabolism and a greater weight-normalized BPA exposure. Because of uncertainty in defining the hepatic BPA intrinsic clearance in adults, these values represent preliminary estimates.

CONCLUSIONS

Simulations of the differential BPA dosimetry between adults and young children point to the need for more sensitive analytical methods for BPA to define, with greater certainty, the adult hepatic BPA intrinsic clearance, as well as a need for external exposure data in young children.

Bioequivalence of two formulations of daidzein administered in a single dose to healthy Chinese volunteers

In this two-treatment, two-period, randomized, crossover bioequivalence study of daidzein, which belongs to the isoflavone class of flavonoids and is classified as a phytoestrogen, two formulations (dripping pills, a rapidly-dissolvable formulation, and tablets) were compared in 20 healthy Chinese male subjects. The drug was given in a single dose of 50 mg and blood samples were withdrawn during 24 h after drug administration. Daidzein was separated and analyzed using a validated liquid chromatography - tandem mass spectrometry (LC-MS/MS) method. The pharmacokinetic parameters were determined from the plasma concentration-time profiles of both formulations. The primary calculated pharmacokinetic parameters were compared statistically to evaluate bioequivalence between the two preparations, using various statistical methods. The analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals fell within the acceptable range (80 - 120%) for bioequivalence. Based on these statistical inferences it can be concluded that the two formulations of daidzein are likely to be bioequivalent.

Development of a physiologically based pharmacokinetic model for bisphenol A in pregnant mice

Bisphenol A (BPA) is a weakly estrogenic monomer used to produce polymers for food contact and other applications, so there is potential for oral exposure of humans to trace amounts via ingestion. To date, no physiologically based pharmacokinetic (PBPK) model has been located for BPA in pregnant mice with or without fetuses. An estimate by a mathematical model is essential since information on humans is difficult to obtain experimentally. The PBPK model was constructed based on the pharmacokinetic data of our experiment following single oral administration of BPA to pregnant mice. The risk assessment of bisphenol A (BPA) on the development of human offspring is an important issue. There have been limited data on the exposure level of human fetuses to BPA (e.g. BPA concentration in cord blood) and no information is available on the pharmacokinetics of BPA in humans with or without fetuses. In the present study, we developed a physiologically based pharmacokinetic (PBPK) model describing the pharmacokinetics of BPA in a pregnant mouse with the prospect of future extrapolation to humans. The PBPK model was constructed based on the pharmacokinetic data of an experiment we executed on pregnant mice following single oral administration of BPA. The model could describe the rapid transfer of BPA through the placenta to the fetus and the slow disappearance from fetuses. The simulated time courses after three-time repeated oral administrations of BPA by the constructed model fitted well with the experimental data, and the simulation for the 10 times lower dose was also consistent with the experiment. This suggested that the PBPK model for BPA in pregnant mice was successfully verified and is highly promising for extrapolation to humans who are expected to be exposed more chronically to lower doses.

Metabolic Barrier against Bisphenol A in Rat Uterine Endometrium

Exposure to environmental chemicals with estrogenic activity during the early stage of pregnancy can seriously affect embryonic development and the maintenance of pregnancy. To estimate the metabolism and pharmacodynamics of a xenoestrogen, bisphenol A, in a reproductive organ, the metabolite of bisphenol A was analyzed after incubating a rat uterine sac in buffer solutions containing the chemical. When the inner or the outer side of the uterine sac was exposed to bisphenol A, the concentration of the parent chemical was decreased in buffer solution and then, only one metabolite, bisphenol A-glucuronide, was observed only in the outer, that is, the maternal, side. A small amount of the parent chemical could pass through the uterine sac without being modified. Uridine diphosphate (UDP)-glucuronosyltransferase (UGT) was shown by immunohistochemical staining analysis to be distributed in epithelial cells of the endometrium, oviduct, and uterine glands. Based on measurements of enzyme activity and on Western blot analysis, UGT activity toward bisphenol A and UGT protein were identified in the microsomal fractions prepared from rat uterus. UGT isoforms, such as UGT1A1, 1A2, 1A5, 1A6, and 1A7, were expressed, and MRP-1 (multidrug resistance-associated protein) and MRP-3, which are well-known to be transporters of various drug-glucuronides, were detected in the rat uterus by reverse transcription-PCR. These results elucidate the rat uterine barrier system by showing that most bisphenol A perfused into the uterus was glucuronidated in the epithelium, resulting in transport of glucuronides to the maternal side.

On the transfer of the Fusarium toxins deoxynivalenol (DON) and zearalenone (ZON) from sows to their fetuses during days 35–70 of gestation

Eleven pregnant sows with a body weight between 153 and 197 kg were fed a control diet (CON, 0.15 mg DON and 0.0035 mg ZON/kg diet) or a diet containing 15% of Fusarium toxin contaminated triticale (MYCO, 4.42 mg DON and 0.048 mg ZON/kg diet) in the period of day 35 and 70 of gestation. The indirect effect of feed intake was separated from the direct effects of the Fusarium toxins by the restricted feeding regimen where all sows were fed the same amount of feed (2000 g/d) over the whole study. At the end of experiment, fetuses were delivered by Caesarian section and samples of serum, bile, urine, liver, kidney and spleen of euthanatized sows and fetuses were taken to analyze the concentrations of DON, ZON and their metabolites. Feeding the Fusarium toxin contaminated diet to pregnant sows caused neither adverse effects on performance, organ weights and maintenance of pregnancy of sows nor on fetus weight and length. Furthermore, no teratogenic or embryolethal effects could be observed in the MYCO group. Hematological and clinical-chemical parameters of sows and fetuses were not affected by feeding, with the exception of significantly lower GLDH (glutamate dehydrogenase) serum activities in MYCO sows. The carry over of DON and ZON from the diet to the sow or fetus tissues was calculated by the diet ratio (sum of concentrations of all metabolites in the physiological specimen divided by the dietary toxin concentration), while the fetus ratio was evaluated by the sum of concentrations of all metabolites in the physiological specimen of the fetus divided by that of the sows. DON and deepoxy-DON were found in urine, bile, serum, liver, kidney and spleen of sows of the MYCO group, but not in the bile of fetuses (spleen not analyzed). ZON and its metabolite alpha-zearalenol (alpha-ZOL) were detected in urine and bile of sows, while all specimens of fetuses as well as serum and liver of sows were negative for ZON metabolites. The maximum diet ratios for urine and bile in sows of the MYCO group were 0.84 and 0.05 for DON metabolites and 1.2 and 3.8 for ZON metabolites, underscoring the differences in metabolism and excretion of both toxins. The maximum diet ratio of DON and deepoxy-DON into liver, kidney and spleen of MYCO sows were 0.003, 0.007 and 0.003, respectively. The maximum fetus ratio of DON and deepoxy-DON into urine, bile, serum, liver and kidney of fetuses were 0.006, 0, 0.5, 0.88, and 0.33, while the maximum placental ratio (sum of toxin concentrations in the physiological specimen of the fetus divided by the toxin serum concentration of the sow) were 0.64, 0, 0.50, 0.70 and 0.52, respectively. Therefore, it can be concluded that the developing fetus is exposed to DON between the gestation days 35 and 70 when the sows are fed a Fusarium toxin contaminated diet. ZON concentration in the MYCO diet was too low to get reliable results for fetus or placental ratios.

Genistein accumulates in body depots and is mobilized during fasting, reaching estrogenic levels in serum that counter the hormonal actions of estradiol and organochlorines

Isoflavones are important dietary compounds that are consumed with the daily diet and elicit important biological actions. Here we report on the ability of genistein to partially accumulate in body depots of male mice, be released following fasting, and modulate the actions of estradiol and environmental estrogens in reproductive and nonreproductive target organs of estrogen-reporter mice (ERE-tK-luciferase). After the consumption of 50 mg/kg/day for 3 days, genistein accumulates in body compartments where it remains at functionally active levels for at least 15 days. Following 48 h of fasting, its concentration increased in serum from 99 +/- 13 to 163 +/- 17 nM. These levels are sufficient to exert an estrogenic effect in the testis and liver, as revealed by a twofold increase in luciferase gene expression. beta-Benzene-hexachloride (betaBHC) given at the concentration of 100 mg/kg/day for 3 days also accumulates in the body and is released by fasting, reaching serum levels of 176 +/- 33 nM, upregulating the luciferase gene in the liver and inhibiting its expression in the testis. When genistein was given in combination with betaBHC at doses sufficient to induce accumulation of both in body depots, the genistein mobilized by fasting reversed the action of the mobilized betaBHC in the testis. Acute administration of nutritional doses of genistein inhibited the action of estradiol and reversed the antiestrogenic action of o,p'-DDT: 1,1,1,-trichloro-2(p-chlorophenyl)-2-(o-chlorophenyl)ethane in the liver and the antiestrogenic action of betaBHC in the testis. Genistein had an additive effect with the ER agonist p,p'-DDT: 1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane in the liver. The observed effects may be relevant to a protective action of phytoestrogens against estrogen receptor-interacting pollutants as well as the dietary modulation of estradiol action.

Review on the toxicity, occurrence, metabolism, detoxification, regulations and intake of zearalenone: An oestrogenic mycotoxin

Zearalenone (ZEA) is a mycotoxin produced mainly by fungi belonging to the genus Fusarium in foods and feeds. It is frequently implicated in reproductive disorders of farm animals and occasionally in hyperoestrogenic syndromes in humans. There is evidence that ZEA and its metabolites possess oestrogenic activity in pigs, cattle and sheep. However, ZEA is of a relatively low acute toxicity after oral or interperitoneal administration in mice, rat and pig. The biotransformation for ZEA in animals involves the formation of two metabolites alpha-zearalenol (alpha-ZEA) and beta-zearalenol (beta-ZEA) which are subsequently conjugated with glucuronic acid. Moreover, ZEA has also been shown to be hepatotoxic, haematotoxic, immunotoxic and genotoxic. The exact mechanism of ZEA toxicity is not completely established. This paper gives an overview about the acute, subacute and chronic toxicity, reproductive and developmental toxicity, carcinogenicity, genotoxicity and immunotoxicity of ZEA and its metabolites. ZEA is commonly found on several foods and feeds in the temperate regions of Europe, Africa, Asia, America and Oceania. Recent data about the worldwide contamination of foods and feeds by ZEA are considered in this review. Due to economic losses engendered by ZEA and its impact on human and animal health, several strategies for detoxifying contaminated foods and feeds have been described in the literature including physical, chemical and biological process. Dietary intakes of ZEA were reported from few countries from the world. The mean dietary intakes for ZEA have been estimated at 20 ng/kgb.w./day for Canada, Denmark and Norway and at 30 ng/kgb.w./day for the USA. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) established a provisional maximum tolerable daily intake (PMTDI) for ZEA of 0.5 microg/kg of body weight.

Evaluation of ex vivo human skin permeation of genistein and daidzein

The percutaneous absorption of genistein (GEN) and daidzein (DAI), whose oestrogenic-like activity is well known, is scantily investigated. In this work the ability of GEN and DAI to reach therapeutic steady-state plasma concentrations following transdermal administration was studied. The skin permeation studies were conducted by using modified Franz diffusion cell and human epidermis as a membrane. PEG400 was the most effective vehicle for both molecules. On the basis of the ex vivo permeation results and estimating therapeutic plasma concentration, we assume that pure GEN can be efficaciously administered by the transdermal route.

Down regulation of bisphenol A glucuronidation in carp during the winter pre-breeding season

Environmental pollution by bisphenol A is prevalent in many rivers. The influence of bisphenol A on the reproductive organs of carp has been demonstrated to be serious, especially in the winter pre-breeding season. Although bisphenol A is detoxified as bisphenol A-glucuronide in carp organs, principally the intestine, the seasonal variation in the efficiency of the detoxification is not known. To estimate the seasonal risk of bisphenol A in carp, we investigated seasonal changes in microsomal UDP-glucuronosyltransferase activity toward bisphenol A in male-carp. Seasonal elimination efficiency of bisphenol A was also examined by organ perfusion in everted intestine. No marked seasonal differences were observed in UDP-glucuronosyltransferase activity toward 1-naphthol, but high activity toward sex steroid hormones (testosterone and estradiol) was observed in the winter pre-breeding season. Low UDP-glucuronosyltransferase activity toward bisphenol A was indicated in winter. The addition of bisphenol A into the mucosal fluid of the everted intestine resulted in excretion of bisphenol A into the mucosal side of the intestine as the metabolite, bisphenol A-glucuronide. Excretion of bisphenol A-glucuronide from carp intestine was highest in summer (proximal intestine: 13.3 nmol; middle intestine: 8.3 nmol; distal intestine: 7.9 nmol) and lowest in winter (proximal intestine: 1.0 nmol; middle intestine: 1.0 nmol; distal intestine: 0.9 nmol). These results suggest that metabolism and excretion of bisphenol A in carp hepatopancreas and intestine are impaired by down regulation of UDP-glucuronosyltransferase activity in the winter pre-breeding season.

Expression of 3alpha- and 3beta-hydroxy steroid dehydrogenase mRNA in COCs and granulosa cells determines Zearalenone biotransformation

Zearalenone (ZEA) is a mycoestrogen found in diverse food and feed materials, particularly in corn and small grains. Following ingestion, the parent zearalenone is converted predominantly into alpha-zearalenol (alpha-ZOL) and beta-zearalenol (beta-ZOL) by hepatic hydroxy steroid dehydrogenases (HSD). The present study demonstrated by standard RT-PCR the expression of 3alpha- and 3beta-HSD also in porcine cumulus oocyte complexes (COCs) and granulosa cells isolated form cumulus oocyte complexes. Analysis of the rate of bioconversion of zearalenone (ZEA) by the cultured granulose cells showed the extra-hepatic production of both hydroxy metabolites of ZEA with alpha-ZOL being the dominating metabolites as previously observed in incubations with liver microsomes. The endogenous steroids 5alpha-dihydrotestosterone (5alpha-DHT), and progesterone (PGTN), both known substrates for 3alpha-HSD inhibited the conversion of ZEA into alpha-ZOL. In the presence of pregnelonone (PGN), a major substrate for 3beta-HSD only a slight inhibitory effect on the apparent beta-ZOL formation could be observed. In conclusion, these data indicate that both 3alpha- and 3beta-HSDs are expressed in porcine COCs and GCs, whereas the biotransformation experiments confirm the involvement of these enzymes in the extra-hepatic biotransformation of ZEA.

CAR and PXR: xenosensors of endocrine disrupters?

The pregnane X-receptor (PXR) and the constitutive androstane receptor (CAR) are orphan nuclear receptors activated by a variety of ligands. Currently it remains uncertain whether these receptors have a high-affinity ligand or instead function as more generalized steroid/xenobiotic sensors. Both receptors are important regulators of several steroid and xenobiotic detoxification enzymes and transporters (phases I-III) in the liver and intestine and thus are important regulators of adaptation to chemical stress. The detoxification proteins induced are responsible for the metabolism, deactivation and transport of bile acids, thyroid and steroid hormones, numerous environmental chemicals, and several drugs. PXR and CAR received their names because of steroid ligands that activate and inhibit their transcriptional activity, respectively. Interestingly, some steroids and steroid mimics activate one or both receptors, including several endocrine disrupting chemicals. Environmental estrogens, such as the pesticides methoxychlor, endosulfan, dieldrin, DDT, and the plasticizer nonylphenol activate either PXR or both PXR and CAR. Because PXR and CAR are activated by numerous steroids and endocrine disrupters, it appears that these receptors protect the integrity of the endocrine system. They recognize an increase in steroid-like chemicals and, in turn, induce detoxification. Furthermore, PXR and CAR induce enzymes, such as the CYP2B and CYP3A family members, responsible for the metabolism of steroid and thyroid hormones and this may alter their normal physiological function. This review summarizes the available data on the activity of endocrine disrupters and endocrine active chemicals on PXR and CAR, examines the role of PXR and CAR in protection from these chemicals, and evaluates potential adverse physiological consequences of PXR and CAR activation.

On the effects ofFusariumtoxin-contaminated wheat and the feed intake level on the metabolism and carry over of zearalenone in dairy cows

The aim was to investigate the effect of feeding Fusarium toxin-contaminated wheat to dairy cows on the metabolism and carry over of zearalenone (ZON) and its metabolites at different feed intakes. Fourteen dairy cows equipped with rumen and duodenal fistulae were used. The experiment consisted of a control period in which the uncontaminated wheat was fed and a mycotoxin period in which the Fusarium toxin-contaminated wheat (8.21 mg deoxynivalenol (DON) and 91 microg ZON kg(-1) dry matter (DM)) was replaced by the control wheat (0.25 mg DON kg(-1) and 51 microg ZON kg(-1) DM). The wheat portion of the concentrate fed daily amounted to 55% on a DM basis. The ration was completed with maize and grass silage (50:50), whereby the maize silage contained 62 microg ZON kg(-1) DM. Feed intakes were adjusted to the current performance of the individual cows. The ZON metabolites alpha-zearalenol (alpha-ZOL) and beta-zearalenol (beta-ZOL) were recovered at the duodenum beside the parent toxin ZON. The recovery of ingested ZON as ZON plus alpha-ZOL plus beta-ZOL at the duodenum ranged between 19 and 247%. The portion of ZON (ranging from 29 to 99%) of the ZON plus alpha-ZOL plus beta-ZOL flow at the duodenum increased significantly with increasing ZON feed intake, whereas the portion of beta-ZOL (up to 57%) decreased significantly. In contrast, portions of ZON in faeces (32-100%), alpha-ZOL (up to 39%) and beta-ZOL (up to 43%) of ZON plus alpha-ZOL plus beta-ZOL were independent of ZON intake. It seems that a lower retention time of the feed and the toxins in the rumen as an effect of the increased feed intake may limit the ruminal metabolization of ZON. The relatively steady recovery of ingested ZON as ZON, alpha-ZOL and beta-ZOL in faeces at the different levels of ZON intake would suggest a further reduction of ZON by intestinal microorganisms. Furthermore, ZON and its metabolites in the milk were lower than the detection limits at daily ZON and DM intakes between 75 and 1125 microg and 5.6 and 20.5 kg day(-1), respectively, and milk yields (fat corrected milk, FCM) between 10 and 42 kg day(-1).

QUANTITATION OF BISPHENOL A AND BISPHENOL A GLUCURONIDE IN BIOLOGICAL SAMPLES BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Bisphenol A (BPA) is a weak estrogen. Pharmacokinetic studies of BPA have demonstrated a rapid and extensive metabolism of BPA to the nonestrogenic BPA-monoglucuronide (BPA-gluc). Some investigators have reported that BPA was found at parts per billion concentrations in the tissues or urine of humans without known exposure to BPA. This work developed a rapid and sensitive method for the determination of BPA and BPA-gluc in plasma and urine based on liquid chromatography-tandem mass spectrometry. The liquid chromatography-electrospray ionization-tandem mass spectrometry method for quantitation of BPA and BPA-gluc uses stable isotope-labeled internal standards. A linear ion trap mass spectrometer permits identification and quantitation of BPA-gluc and BPA without sample workup. Development of separation conditions reduced the BPA-background in solvent samples to below 2.5 pmol/ml for BPA. Limit of quantitation (LOQ) for BPA in control urine was 15 pmol/ml; LOQ for BPA-gluc was 65 pmol/ml. Application of the method to urine samples from human subjects (n = 6) after administration of 25 microg of BPA/person (estimated maximum human daily intake) permitted the determination of excretion kinetics for BPA-gluc; BPA was below the LOD in all except two of the samples. In urine or blood samples of human subjects (n = 19) without intentional exposure to BPA, BPA concentrations were always below the limit of detection ( approximately 2.5 pmol/ml) with or without prior glucuronidase treatment. The results show that care is required for analysis of BPA and its major metabolite BPA-gluc. The LOD obtained and the absence of detectable levels of BPA in samples from individuals suggests that general exposure of humans to BPA is much lower than the worst-case exposure scenario developed.

Kinetics and metabolism of zearalenone in young female pigs

The fate of a single bolus of the Fusarium mycotoxin zearalenone (ZON) given intravenously to pigs was followed up. Pigs were equipped with duodenal re-entrant cannulas, post-valvular T-shape cannulas and with a urinary bladder balloon catheter. The animals were divided into three groups. Pigs of the control group were injected with ZON (Co), and pigs of the second group were also injected with ZON but their duodenal digesta was quantitatively exchanged for 12 h with corresponding pigs of the third group, not injected with ZON. Therefore, the second group had a disrupted entero-hepatic cycling of ZON (DEHC) and the third one had an induced entero-hepatic cycling of ZON (IEHC). The kinetic profile of ZON and its metabolites in plasma and their flow with urine, duodenal and ileal digesta and with faeces was examined over the next 72 h after the bolus was given. Eleven days later, pigs were slaughtered for collection of bile, urine and liver to analyse ZON residues. In all specimens examined, alpha-zearalenol (ZOL) was detected as the only metabolite of ZON. Kinetic evaluation of the plasma data revealed that the terminal elimination half-life of ZON was reduced from 2.63 h in pigs of Co-group to 1.1 h when EHC of ZON was disrupted for 12 h (DEHC-group). The maximum ZON concentration in plasma of pigs with the IEHC was found at 2.73 h after the bolus was given to their counterparts. The percentage of the alpha-ZOL- and ZON-area under the curves (AUC) estimated for the IEHC-group amounted to approximately 18% of the corresponding AUC of the Co-group which would suggest that a substantial proportion of both substances are re-cycled via entero-hepatic re-circulation. Cumulative recovery of ZON and alpha-ZOL, expressed as percentage of the ZON-bolus was characterized by a saturation kinetics in urine and duodenal digesta, and after 72 h, the respective values for Co-, DEH-, and IEHC-groups were 70%, 55% and 12%; and 35%, 22% and 11%. Faecal excretion started to increase steeply after 48 h and still continued to increase after 72 h when the cumulative excretion was 6%, 3% and 2% for Co-, DEHC- and IEHC-groups respectively. Fourteen days after the bolus injection, ZON and alpha-ZOL concentrations in bile, liver and urine were lower than the detection limits of the applied method. The results would suggest that within this period of time a massive single bolus of ZON is nearly completely eliminated from the body.

Validated liquid chromatography-tandem mass spectrometric method for the quantitative determination of daidzein and its main metabolite daidzein glucuronide in rat plasma

A highly selective and sensitive liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed and validated to determine daidzein and its main metabolite daidzein glucuronide in rat plasma. The analytes and internal standard genistein were extracted from plasma samples by n-hexane-diethyl ether (1:4, v/v), and separated on a C18 column. The mobile phase consisted of acetonitrile-water-formic acid (80 : 20: 1, v/v/v). Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via atmospheric pressure chemical ionization (APCI) source. The method has a limit of quantification of 0.24 ng/ml. The linear calibration curves were obtained in the concentration range of 0.24-1000 ng/ml. The intra- and inter-day precisions were lower than 13.2% in terms of % RSD. The accuracy ranged from -0.5% to 2.4% in terms of % RE (relative error). This method was successfully applied to the determination of plasma concentration of daidzein and its main metabolite daidzein glucuronide in rats after an oral administration of 20 mg/kg daidzein.

Prevention of zearalenone-induced hyperestrogenism in prepubertal mice

Previous methods for the control of zearalenone (ZEN)-induced hyperestrogenism in animals have proven largely ineffective. The main objective in this study was to identify an enterosorbent that decreases the dietary bioavailability, and subsequent estrogenic effects, of ZEN. Initial in vitro screenings in aqueous solution (4 microg ZEN/ml) indicated that an activated carbon (AC) was the most efficient sorbent (99%), followed by a combination of 2 parts AC plus 3 parts HEC (hectorite) (69%), cetylpyridinium-exchanged low-pH montmorillonite (CP-LPHM) clay (58%), hexadecyltrimethylammonium-exchanged low-pH montmorillonite (HDTMA-LPHM) clay (54%), and HEC alone (28%). Results from the adult hydra bioassay suggested that the addition of either AC or HEC effectively decreased the effects of ZEN on Hydra attenuata without toxicity, as was observed with the use of either CP-LPHM or HDTMA-LPHM. Based on these results, AC, HEC, and 2AC:3HEC were evaluated in prepubertal mice. At a dietary inclusion level of 0.8% (w/w), AC alone significantly protected mice against the estrogenic effects induced by 35 mg ZEN/kg feed. Inclusion of 1.2% HEC with the 0.8% AC showed no additional protection; whereas 1.2% HEC alone failed to decrease the estrogenic effects. Ground flaxseed (25% w/w) in the diet also elicited protection, but to a lesser extent. Preliminary studies suggested that three similar carbons failed to decrease ZEN bioavailability. These findings suggest that the AC used in this study may be efficacious as an enterosorbent in animals consuming ZEN-contaminated diets. However, further studies are needed to evaluate the binding specificity, as well as the safety of chronic exposure.

Evaluation of Oral and Intravenous Route Pharmacokinetics, Plasma Protein Binding, and Uterine Tissue Dose Metrics of Bisphenol A: A Physiologically Based Pharmacokinetic Approach

Bisphenol A (BPA) is a weakly estrogenic monomer used in the production of polycarbonate plastic and epoxy resins, both of which are used in food contact and other applications. A physiologically based pharmacokinetic (PBPK) model of BPA pharmacokinetics in rats and humans was developed to provide a physiological context in which the processes controlling BPA pharmacokinetics (e.g., plasma protein binding, enterohepatic recirculation of the glucuronide [BPAG]) could be incorporated. A uterine tissue compartment was included to allow the correlation of simulated estrogen receptor (ER) binding of BPA with increases in uterine wet weight (UWW) in rats. Intravenous- and oral-route blood kinetics of BPA in rats and oral-route plasma and urinary elimination kinetics in humans were well described by the model. Simulations of rat oral-route BPAG pharmacokinetics were less exact, most likely the result of oversimplification of the GI tract compartment. Comparison of metabolic clearance rates derived from fitting rat i.v. and oral-route data implied that intestinal glucuronidation of BPA is significant. In rats, but not humans, terminal elimination rates were strongly influenced by enterohepatic recirculation. In the absence of BPA binding to plasma proteins, simulations showed high ER occupancy at doses without uterine effects. Restricting free BPA to the measured unbound amount demonstrated the importance of including plasma binding in BPA kinetic models: the modeled relationship between ER occupancy and UWW increases was consistent with expectations for a receptor-mediated response with low ER occupancy at doses with no response and increasing occupancy with larger increases in UWW.

Physiologically based pharmacokinetics of bisphenol A

A physiologically based pharmacokinetic (PBPK) model consisting of vein, artery, lung, liver, spleen, kidneys, heart, testes, muscle, brain, adipose tissue, stomach, and small intestine was developed to predict the tissue distribution and blood pharmacokinetics of bisphenol A in rats and humans. To demonstrate the validity of the developed PBPK model, bisphenol A was administered to rats by multiple iv injections to steady state. The PBPK model predicted the steady-state levels of bisphenol A in blood and various tissues observed in rats after multiple iv injections. The PBPK model was further applied to predict blood and various tissue levels of bisphenol A in a 70 kg-human after single iv injection (5-mg dose) and multiple oral administrations to steady state (100-mg doses every 24 h). The simulated steady-state human blood levels (0.9-1.6 ng/ml) were comparable to basal blood levels of bisphenol A reported in literature (1.49 ng/ml). Furthermore, pharmacokinectic parameters of CL (116.6 L/h), Vss (141.8 L), and t1/2 (76.8 min) predicted for humans were comparable to those previously predicted by simple allometric scaling. This PBPK model may provide insights into the tissue distribution characteristics as a result of human exposure to bisphenol A.

Disposition of low doses of 14C-bisphenol A in male, female, pregnant, fetal, and neonatal rats

Bisphenol A (BPA) is a weak xenestrogen (ADI = 50 microg kg(-1), US EPA) which is mass-produced, with potential for human exposure. To study absorption, distribution, excretion, and metabolism of BPA, BPA labeled with carbon-14 was administered p.o. to male and female Fischer (F344) rats at relatively low doses (20, 100, and 500 microg kg(-1)), and i.v. injected at 100 and 500 microg kg(-1). 14C-BPA (500 microg kg(-1)) was also administered orally to pregnant and lactating rats to examine the transfer of radioactivity to fetuses, neonatal rats, and milk. Radioluminographic determination using phosphor imaging plates was employed to achieve highly sensitive determination of radioactivity. Absorption ratios of radioactivity after three oral doses were high (35-82%); parent 14C-BPA in the circulating blood was quite low, however, suggesting considerable first-pass effect. After an oral dose of 100 microg kg(-1) 14C-BPA, the radioactivity was distributed and eliminated rapidly, but remained in the intestinal contents, liver, and kidney for 72 h. The major metabolite in the plasma and urine was BPA glucuronide, whereas most of the BPA was excreted with the feces as free BPA. A second peak in the time-course of plasma radioactivity suggested enterohepatic recirculation of BPA glucuronide. There was limited distribution of 14C-BPA to the fetus and neonate after oral administration to the dam. Significant radioactivity was not detected in fetuses on gestation days 12 and 15. On day 18, however, radioactivity was detected in the fetal intestine and urinary bladder 24 h after oral dosing of 14C-BPA to the pregnant rats. Part of radioactivity was transferred to neonatal rats from the milk of the treated lactating dam and remained in the intestine of the neonates after 24-h nursing by an untreated dam.

Functional changes in dopamine D3 receptors by prenatal and neonatal exposure to an endocrine disruptor bisphenol-A in mice

Bisphenol-A (BPA), one of the most common environmental endocrine disrupters, has been evaluated extensively for toxicity and carcinogenicity. However, little is still known about its action on the central nervous system (CNS). In the previous study, we found that prenatal and neonatal exposure to BPA markedly enhanced the rewarding effect induced by morphine. Here we found that prenatal and neonatal exposure to BPA resulted in the attenuation of dopamine D3 receptor-mediated G-protein activation by 7-OH-DPAT in the mouse limbic forebrain. This treatment also caused a significant decrease in the B(max) value of [(3)H]PD128907, a dopamine D3 receptor ligand, in this area. Under these conditions, no change in dopamine D3 receptor mRNA expression in the limbic forebrain and lower midbrain was observed by prenatal and neonatal exposure to BPA. The present data provide further evidence that prenatal and neonatal exposure to BPA leads to the reduction of functional dopamine D3 receptors without affecting the new synthesis of dopamine D3 receptors in the mouse limbic forebrain.

Age and Dose Dependency of the Pharmacokinetics and Metabolism of Bisphenol A in Neonatal Sprague-Dawley Rats Following Oral Administration

Previous studies demonstrated the rapid clearance of bisphenol A (BPA) from blood following oral administration to adult rats with the principal metabolite being BPA-monoglucuronide (BPA-glucuronide). Since the ontogeny of glucuronyl transferases (GT) differs with age, the pharmacokinetics of BPA were studied in neonatal animals. (14)C-BPA was administered via gavage at 1 or 10 mg/kg body weight to rats at postnatal day (pnd) 4, pnd 7, pnd 21, or to 11 week old adult rats (10 mg/kg dose only). Blood (neonates and adults) and selected tissues (neonates) were collected at 0.25, 0.75, 1.5, 3, 6, 12, 18, and 24 h postdosing. BPA and BPA-glucuronide in the plasma were quantified by high-performance liquid chromatography; radioactivity in the plasma and tissues was quantified by liquid scintillation spectrometry. The data indicate that neonatal rats at all three ages metabolized BPA to BPA-glucuronide, although an age dependency in the number and concentration of plasma metabolites was observed, consistent with the ontogeny of GT. BPA-glucuronide and BPA concentrations in the plasma were greater in neonates than in adults, except at 24 h postdosing, suggesting an immaturity in the development of hepatic excretory function in neonatal rats. Nevertheless, the half-lives for the elimination of BPA-glucuronide in plasma were more rapid in neonatal animals than in adults, likely due to reduced microflora beta-glucuronidase activity and an absence of enterohepatic recirculation. A dose dependency in the metabolism and pharmacokinetics of BPA administered to neonates was also observed with nearly complete metabolism of BPA to BPA-glucuronide (94-100% of the plasma radioactivity) at a dose of 1 mg/kg. This was in contrast to finding up to 13 different plasma metabolites observed at the 10 mg/kg dose. These data indicate that, from early in neonatal life through pnd 21, there is sufficient GT activity in rats to efficiently metabolize BPA to its nonestrogenic metabolite at low doses.

Estrogenic effects in flounder Platichthys flesus orally exposed to 4-tert-octylphenol

The estrogenic effect of dietary 4-tert-octylphenol in the flounder Platichthys flesus was investigated in the laboratory. In the first experiment male flounders were fed doses of 10, 50 and 100 mg 4-tert-octylphenol kg(-1) BW or 0.05 mg 17beta-estradiol kg(-1) BW every second day for 10 days. Increases in the plasma content of vitellogenin were observed on day 6 by the first sampling in all treated groups. An effect of octylphenol on the size of the liver and testis was only seen in one of the exposed group (50 mg 4-tert-octylphenol kg(-1) BW). An increase in the concentration of 4-tert-octylphenol was found in both liver and muscle tissues of all 4-tert-octylphenol treated fish. The concentration of 4-tert-octylphenol (ng g(-1) WW) in liver tissue was four to five times greater than the concentration in muscle tissue. Only about 8% of the 4-tert-octylphenol administered to the group receiving 50 mg 4-tert-octylphenol kg(-1) BW was retained in the liver and the muscles at the end of the experiment. In the second experiment male flounders were exposed to a low dose range of 4-tert-octylphenol (1 to 25 mg 4-tert-octylphenol kg(-1) BW) in order to establish the dose-response relationship of 4-tert-octylphenol when applied by feeding to flounder. Vitellogenin induction (LOED) occurred at 10 and 5 mg 4-tert-octylphenol kg(-1) BW after, respectively, 6 and 11 days of exposure. Based on a logistic regression analysis the effect dose (ED(50)) could be determined as 8.2 and 5.6 mg 4-tert-octylphenol kg(-1) BW on day 6 and 11, respectively. 4-tert-octylphenol accumulated in liver, muscle and testis tissue, and a significant accumulation in liver was found at 2.5 mg 4-tert-octylphenol kg(-1) BW and in muscle and testis at 5 mg 4-tert-octylphenol kg(-1) BW. Finally, a positive correlation between the plasma vitellogenin concentration and the liver tissue concentration of 4-tert-octylphenol was established as well as a positive correlation between the content of 4-tert-octylphenol in liver and muscle/testis tissue.

Bioavailability of phyto-oestrogens

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

Disposition of a low dose of 14C-bisphenol A in male rats and its main biliary excretion as BPA glucuronide

Bisphenol A (BPA) is a weak xenoestrogen mass-produced with potential human exposure. The disposition of bisphenol A in male Fischer-344 (F344) rats dosed orally (100 or 0.10 mg/kg) or intravenously (0.10 mg/kg) was determined. Smaller amounts of the dose appeared in the urine. The main excretion route was feces in rats irrespective of dose and administration route. The biliary excretion during 6 h was 58-66% after iv dosing and 45-50% after oral dosing at 0.10 mg 14C-BPA/kg. Toxicokinetic parameters obtained from 14C-BPA-derived radioactivity in blood were the terminal elimination half-life, t1/2beta = 39.5 h, and total body clearance, CLtot = 0.52 l/h/kg after iv dosing of 0.10 mg 14C-BPA/kg to male rats. The blood concentration reached its maximum of 5.5 ng-eq/ml at 0.38 h after oral dose. AUC(0-6 h), AUC(0-48 h), and AUCinf of 14C-BPA-derived radioactivity, were 34, 118, and 192 ng-eqh/ml for the iv dose and 18, 102, and 185 ng-eqh/ml for the oral dose, respectively. The oral bioavailability of F(0-6 h), F(0-48 h), and Finf were 0.54, 0.86, and 0.97, respectively. The 14C-BPA-derived radioactivity was strongly bound to plasma protein (free fraction, fu = 0.046) and preferentially distributed to the plasma with a blood/plasma ratio of 0.67. From the bile of male rats orally dosed at 100 mg/kg, we have isolated and characterized BPA glucuronide (BPA-gluc) by ESI/MS, 1H and 13C NMR spectroscopy. HPLC analysis showed that BPA-gluc was the predominant metabolite in bile and urine. Unchanged BPA was mostly detected in feces. These results suggest that BPA is mainly metabolized to BPA-gluc and excreted into feces through the bile and subject to enterohepatic circulation in rats irrespective of dose and administration route.

The effects of phytoestrogenic isoflavones on the formation and disposition of paracetamol sulfate in the isolated perfused rat liver

This study examines the potential for the phytoestrogenic isoflavones, a type of complementary medicine, to be involved in pharmacokinetic interactions in the liver. Rat livers were isolated and perfused to steady state, in single-pass mode, with either 5 microM paracetamol (n = 6), or 5 microM paracetamol with a 50:50 molar mixture of genistein and biochanin A or daidzein and formononetin, at a total isoflavone concentration of 1 and 10 microM (n = 6 for each mixture at each concentration). At 1 microM, neither isoflavone mixture had any effect, while at 10 microM both mixtures decreased the clearance of paracetamol and the formation clearance to paracetamol sulfate. Genistein and biochanin A (10 microM) also increased the biliary extraction of hepatically-generated paracetamol sulfate. Additional livers were perfused with an infusion of 5 microM (14)C-paracetamol in the absence (n = 4), or presence, of a 10 microM genistein and biochanin A mixture (n = 4). Analysis of washout perfusate and bile samples (up to 30 min after stopping the infusion) revealed that the isoflavones reduced the first-order rate constant for paracetamol sulfate transport into perfusate, but not for transport into bile. The results indicate that isoflavones can reduce the formation of paracetamol sulfate and that its enhanced excretion into bile arises from the inhibition of sinusoidal efflux transport.

Evaluation of the estrogenic effects of legume extracts containing phytoestrogens

Seven legume extracts containing phytoestrogens were analyzed for estrogenic activity. Methanol extracts were prepared from soybean (Glycine max L.), green bean (Phaseolus vulgaris L.), alfalfa sprout (Medicago sativa L.), mung bean sprout (Vigna radiata L.), kudzu root (Pueraria lobata L.), and red clover blossom and red clover sprout (Trifolium pratense L.). Extracts of kudzu root and red clover blossom showed significant competitive binding to estrogen receptor beta (ERbeta). Estrogenic activity was determined using an estrogen-dependent MCF-7 breast cancer cell proliferation assay. Kudzu root, red clover blossom and sprout, mung bean sprout, and alfalfa sprout extracts displayed increased cell proliferation above levels observed with estradiol. The pure estrogen antagonist, ICI 182,780, suppressed cell proliferation induced by the extracts, suggesting an ER-related signaling pathway was involved. The ER subtype-selective activities of legume extracts were examined using transiently transfected human embryonic kidney (HEK 293) cells. All seven of the extracts exhibited preferential agonist activity toward ERbeta. Using HPLC to collect fractions and MCF-7 cell proliferation, the active components in kudzu root extract were determined to be the isoflavones puerarin, daidzin, genistin, daidzein, and genistein. These results show that several legumes are a source of phytoestrogens with high levels of estrogenic activity.

Phytoestrogens and prostate cancer

Androgcns are required to maintain the integrity of the prostate and the survival of androgen dependent epithelial cells within the gland. Anti-androgens arc the primary treatment strategy for non-localized prostate cancer, but ultimately fail over time with the development of androgen independent tumors. Estrogens affect the growth and development of the prostate and may affect the development of prostate cancer. Because of the side effects of estrogen treatment alternative therapies include the use of phytoestrogens as chemopreventative and chemotherapeutic treatment modalities. Phytoestrogens, can cause growth arrest and in some cases apoptosis in prostate cancer cells in vivo and in vitro. This may be due to the estrogenic properties of the compounds or alternative mechanisms of action. A number of phytoestrogens have been shown to have anti-androgenic effects and anti-oxidant activities. Other mechanisms include inhibition of 5alpha-reductase, 17beta-hydroxysteroid dehydrogenase, aromatase, tyrosine specific protein kinases and DNA topoisomerase II. This review examines the possible relation between phytoestrogens and prostate cancer and their possible use in prostate cancer prevention or management.

Quantitative structure-activity relationships for estrogen receptor binding affinity of phenolic chemicals

The estrogen receptor (ER) binding affinities of 25 compounds including 15 industrial phenolic chemicals, two phytoestrogens, three natural steroids and one man-made steroid were detected by a binding competition assay. The 17 industrial phenolic chemicals were selected as objective compounds because they are possibly released from epoxy and polyester-styrene resins used in lacquer coatings of concrete tank and lining of steel pipe in water supply system. A quantitative structure-activity relationship (QSAR) for structurally diverse phenols, nine alkylphenols with only one alkyl group, four hydroxyl biphenyls, bisphenol A and four natural and man-made estrogens was established by applying a quantum chemical modeling method. Logarithm of octanol-water coefficient (logPow), molecular volume (V(m)), and energies of the highest occupied molecular orbital ( epsilon (HOMO)) and lowest unoccupied molecular orbital ( epsilon (LUMO)) were selected as hydrophobic, steric (V(m)), and electronic chemical descriptors, respectively. Chemicals capable of ER binding had large V(m) and high epsilon (HOMO), while the effects of logPow and epsilon (LUMO) on the binding affinity could not be identified. The QSAR made successful predictions for the three phytoestrogens. Also, the successful prediction of ER-binding affinity for biochanin A, another phytoestrogen, two indicators of pH (phenolphthalin and phenolphthalein) and one alkylphenolic chemical with three alkyl groups (4-methyl-2,6-di-butyl-phenol), by amending the V(m) in the above-mentioned QSAR according to the electron-density distribution (or HOMO density) is an additional step in the elucidation of chemical steric and electronic parameters for predicting the binding affinities of phenolic compounds.

Isoflavonoid and lignan phytoestrogens as dietary biomarkers

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

Potential risks and benefits of phytoestrogen-rich diets

Interest in the physiological role of bioactive compounds present in plants has increased dramatically over the last decade. Of particular interest in relation to human health are the class of compounds known as the phytoestrogens, which embody several groups of non-steroidal oestrogens including isoflavones & lignans that are widely distributed within the plant kingdom. Data from animal and in vitro studies provide plausible mechanisms to explain how phytoestrogens may influence hormone dependent states, but although the clinical application of diets rich in these oestrogen mimics is in its infancy, data from preliminary studies suggest potential beneficial effects of importance to health. Phytoestrogens are strikingly similar in chemical structure to the mammalian oestrogen, oestradiol, and bind to oestrogen receptors (ER) with a preference for the more recently described ER beta. This suggests that these compounds may exert tissue specific effects. Numerous other biological effects independent of the ER (e.g. antioxidant capacity, antiproliferative and antiangiogenic effects) have been ascribed to these compounds. Whether phytoestrogens have any biological activity in humans, either hormonal or non hormonal is a contentious issue and there is currently a paucity of data on human exposure. Much of the available data on the absorption and metabolism of dietary phytoestrogens is of a qualitative nature; it is known that dietary phytoestrogens are metabolised by intestinal bacteria, absorbed, conjugated in the liver, circulated in plasma and excreted in urine. Recent studies have addressed quantitatively what happens to isoflavones following ingestion--with pure compound and stable isotope data to compliment recent pharmacokinetic data for soy foods. The limited studies conducted so far in humans clearly confirm that soya isoflavones can exert hormonal effects. These effects may be of benefit in the prevention of many of the common diseases observed in Western populations (such as breast cancer, prostate cancer, menopausal symptoms, osteoporosis) where the diet is typically devoid of these biologically active naturally occurring compounds. However since biological effects are dependent on many factors including dose, duration of use, protein binding affinity, individual metabolism and intrinsic oestrogenic state, further clinical studies are necessary to determine the potential health effects of these compounds in specific population groups. However we currently know little about age related differences in exposure to these compounds and there are few guidelines on optimal dose for specific health outcomes.

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Phytoestrogens: pharmacological and therapeutic perspectives

Phytoestrogens exert different estrogen receptor-dependent and -independent pharmacological actions. They share with estrogens several structural features and show greater affinity for the newly described estrogen receptor-beta. Many hope that phytoestrogens can exert the cardioprotective, anti-osteoporotic and other beneficial effects of the estrogens used in hormone replacement therapy in postmenopausal women without adversely affecting the risk of thrombosis and the incidence of breast and uterine cancers. Although there are many positive indications that phytoestrogens can fulfil this role, it remains to be proven: controlled interventional studies are lacking, and many questions remain unanswered. This review analyzes, on the basis of available experimental and epidemiological studies, the pros and cons of phytoestrogen use and describes the potential tissue targets and mechanisms of action of phytoestrogens.

Evaluating bioaccumulation of suspected endocrine disruptors into periphytons and benthos in the Tama River

There are two major routes through which fish are exposed to endocrine disruptors (EDs); one route is through water that is a habitat; the other is through aquatic food such as algae and benthos. Few studies on the bioaccumulation of EDs in food have been conducted. Therefore, we evaluated the concentration in food of nonylphenol (NP), bisphenol A (BPA) and 17beta-estradiol (E2), which were frequently detected in river water and in final discharge of Wastewater Treatment Plants (WWTPs) in Japan. We also evaluated the estrogenicity of samples using recombinant yeast. NP concentrations ranged 0.1-0.4 microg/L in the river water, while they ranged 8-130 microg/kg-wet in the periphytons and 8-140 microg/kg-wet in the benthos. BPA concentrations ranged 0.02-0.15 microg/L in the river water, while they ranged 2-8.8 microg/kg-wet in the periphytons and 0.3-12 microg/kg-wet in the benthos. E2 concentrations ranged 0.0001-0.0076 microg/L in the water, while they ranged 0.09-2.26 microg/kg-wet in the periphytons and <0.01-0.22 microg/kg-wet in the benthos. The estrogenicity ranged 0.0001-0.0464 microg-E2equivalent/L in the water, while it ranged 3.4-66.8 microg-E2equivalent/kg-wet in the periphytons and 7.4-5458 microg-E2equivalent/kg-wet in the benthos. Bioaccumulation factors of NP are estimated as 160-650 for the periphytons, and 63-990 for the benthos, respectively. Bioaccumulation factors of BPA are estimated as 18-650 for the periphytons, and 8-170 for the benthos, respectively. Bioaccumulation factors of E2 are estimated as 64-1,200 for the periphytons, and 100-160 for the benthos, respectively. The ratios of the periphytons and the benthos to the water in terms of the estrogenicity were larger than those in terms of the chemicals. In particularly, the ratio of the benthos to the water is about 10(6) in the maximum. The results suggest that food may be a more important route for fish exposed to EDs in water environment.

Xenoestrogen exposure and mechanisms of endocrine disruption

Environmental xenoestrogens can be divided into natural compounds (e.g. from plants or fungi), and synthetically derived agents including certain drugs, pesticides and industrial by-products. Dietary exposure comes mainly from plant-derived phytoestrogens, which are thought to have a number of beneficial actions. However, high levels of exogenous estrogens including several well-known synthetic agents are associated with harmful effects. Chemicals like xenoestrogens, which can mimic endogenous hormones or interfere with endocrine processes, are collectively called endocrine disruptors. Adverse effects by endocrine disrupting chemicals (particularly xenoestrogens) include a number of developmental anomalies in wildlife and humans. Critical periods of urogenital tract and nervous system development in-utero and during early post-natal life are especially sensitive to hormonal disruption. Furthermore, damage during this vulnerable time is generally permanent, whereas in adulthood, ill effects may sometimes be alleviated if the causative agent is removed. The most commonly studied mechanism in which xenoestrogens exert their effects is through binding and activation of estrogen receptors a and similar to endogenous hormone. However, endocrine disruptors can often affect more than one hormone (sometimes in opposite directions), or different components of the same endocrine pathway, therefore making it difficult to predict effects on human health. In addition, xenoestrogens have the potential to exert tissue specific and nongenomic actions, which are sensitive to relatively low estrogen concentrations. The true risk to humans is a controversial issue; to date, little evidence exists for clear-cut relationships between xenoestrogen exposure and major human health concerns. However, because of the complexity of their mechanism and potential for adverse effects, much interest remains in learning how xenoestrogens affect normal estrogen signaling.

Benzophenone-induced estrogenic potency in ovariectomized rats

To assess the estrogenic potency of benzophenone by in-vivo uterotrophic assay, we gave orally either the compound (100 or 400 mg/kg) or 17beta-estradiol (0.2 mg/kg) as a positive control, once per day for 3 days, to ovariectomized Sprague-Dawley (SD) rats, and all rats were killed 24 h after being given the last dose. The high dose of benzophenone elicited an approximately 1.9-fold increase in absolute and relative uterine weight, and 17beta-estradiol increased uterine weight approximately fivefold relative to the control. The uterine response caused by both compounds was accompanied by an increase in luminal epithelium height and stromal cell numbers in the uterus and an increase in the thickness of vaginal epithelium cell layers with cornification. At 24 h after the last dose, the mean serum concentrations of benzophenone, benzhydrol and p-hydroxybenzophenone in the high-dosed rats were 10.4+/-1.0, 1.5+/-0.3, and 0.7+/-0.2 (mean +/- SE) micro mol/l, respectively, whereas in the serum of low-dosed rats these compounds were not detected. When a single oral administration of benzophenone (100 or 400 mg/kg) was given to intact female rats, serum concentrations of benzophenone, benzhydrol and p-hydroxybenzophenone increased in a dose-dependent manner 6 h later. Previously, Nakagawa et al. (2000) and Nakagawa and Tayama (2001) reported that the subcutaneous injection of p-hydroxybenzophenone into juvenile female rats elicited estrogenic activity in reproductive organs, whereas neither benzophenone nor benzhydrol had such an effect. In addition, p-hydroxybenzophenone itself rather than the parent compound caused a proliferation of estrogen receptor-positive MCF-7 cells in vitro. Based on these findings, it is apparent that the pro-estrogenic compound benzophenone requires biotransformation to p-hydroxybenzophenone, a metabolite with intrinsic hormonal activity.