Metabolism and interaction of bisphenol A in human hepatic cytochrome P450 and steroidogenic CYP17

Unveiling the intricacies of BPA and BPS: comprehensive insights into its toxic effects using a cutting-edge microphysiological system

Concerns over Bisphenol A (BPA) and its substitute, Bisphenol S (BPS), have led to innovative exploration due to potential adverse health effects. BPS, replacing BPA in some regions to avoid toxic impacts, remains insufficiently studied. Besides this, the organ-on-a-chip technology emerges as a transformative solution in drug discovery and chemiclas toxicity testing, minimizing costs and aligning with ethical standards by reducing reliance on animal models, by integrating diverse tissues and dynamic cell environments enhances precision in predicting organ function. Here, we employ a 3-organ-on-a-chip microfluidic device with skin, intestine, and liver cultures to assess the effects of BPA and BPS via topical and oral administration. Our evaluation focused on gene markers associated with carcinogenicity, systemic toxicity, and endocrine disruption. BPA exhibited expected absorption profiles, causing liver injury and genetic modulation in related pathways. BPS, a safer alternative, induced adverse effects on gene expression, particularly in topical absorption, with distinct absorption patterns. Our findings underscore the urgency of addressing BPA and BPS toxicity concerns, highlighting the crucial role of organ-on-a-chip technology in understanding associated health risks. The study promotes the organ-on-a-chip methodology as a valuable tool for safe drug development and disease treatments, offering a novel liver toxicity screening alternative to traditional animal tests. This contributes to advancing comprehension of the biological effects of these compounds, fostering improved safety assessments in human health.

Construction of a fused grid-based CYP2C18-Template system and its application to drug metabolism

Detailed estimation of cytochrome P450 (CYP)-mediated metabolisms of medicine and other chemicals is necessary for the efficacy and safety assessments. Data on the metabolisms mediated by minor CYP enzymes like CYP2C18 are often not available in metabolisms and safety assessments of chemicals except for medical drugs developed recently. A ligand-accessible space in the active site of human CYP2C18 was thus reconstituted as a fused grid-based Template with the use of structural data of its ligands. An evaluation system of CYP2C18-mediated metabolism was then developed on Template with the introduction of the idea of movement and fastening of ligands after Trigger-residue contact. Reciprocal comparison of the data of simulations on Template with experimental results suggested a unified way of the interaction of CYP2C18, in similar to the CYP2C8 interaction (Drug Metab Pharmacokinet 2023, in press). These experiments also displayed the roles of initial Trigger-residue-localizations on their distinct catalyses among human CYP2C enzymes. Simulation experiments for over 130 reactions of CYP2C18 ligands supported the system established.

Relationship between bisphenol A and autoimmune thyroid disease in women of childbearing age

Background

Autoimmune thyroid disease (AITD) is the main cause of hypothyroidism in women of childbearing age. Bisphenol A (BPA) is an environmental factor affecting AITD. This study aims to investigate relationship between BPA and AITD in women of childbearing age, thereby contributing novel evidence for the prevention of hypothyroidism in this specific demographic.

Methods

A total of 155 women of childbearing age were enrolled in this study, including the euthyroid group comprised 60 women with euthyroidism and thyroid autoantibodies negativity and the AITD group consisted of 95 women with euthyroidism and at least one thyroid autoantibody positivity. The general information, thyroid function, thyroid autoantibodies, and thyroid ultrasound results of the two groups of women of childbearing age were recorded. Urinary BPA and urinary BPA/creatinine were detected. The difference of BPA levels between the two groups was compared. logistic regression was used to analyze the correlation between BPA and AITD.

Results

The proportion of multiparous and serum thyroid stimulating hormone levels were significantly higher in the AITD group compared to the euthyroid group. Logistic regression analysis revealed that BPA levels did not exhibit a statistically significant association with AITD. Spearman correlation analysis revealed a statistically significant correlation between BPA and urinary iodine levels (r=0.30, P < 0.05), as well as a correlation between urinary BPA and free tetraiodothyronine (FT4) levels (r=0.29, P < 0.05).

Conclusion

This study revealed a correlation between urinary BPA levels and FT4 levels. However, it did not establish a relationship between BPA and AITD in women of childbearing age.

Biotransformation of Bisphenol by Human Cytochrome P450 2C9 Enzymes: A Density Functional Theory Study

Bisphenol A (BPA, 2,2-bis-(4-hydroxyphenyl)propane) is used as a precursor in the synthesis of polycarbonate and epoxy plastics; however, its availability in the environment is causing toxicity as an endocrine-disrupting chemical. Metabolism of BPA and their analogues (substitutes) is generally performed by liver cytochrome P450 enzymes and often leads to a mixture of products, and some of those are toxic. To understand the product distributions of P450 activation of BPA, we have performed a computational study into the mechanisms and reactivities using large model structures of a human P450 isozyme (P450 2C9) with BPA bound. Density functional theory (DFT) calculations on mechanisms of BPA activation by a P450 compound I model were investigated, leading to a number of possible products. The substrate-binding pocket is tight, and as a consequence, aliphatic hydroxylation is not feasible as the methyl substituents of BPA cannot reach compound I well due to constraints of the substrate-binding pocket. Instead, we find low-energy pathways that are initiated with phenol hydrogen atom abstraction followed by OH rebound to the phenolic ortho- or para-position. The barriers of para-rebound are well lower in energy than those for ortho-rebound, and consequently, our P450 2C9 model predicts dominant hydroxycumyl alcohol products. The reactions proceed through two-state reactivity on competing doublet and quartet spin state surfaces. The calculations show fast and efficient substrate activation on a doublet spin state surface with a rate-determining electrophilic addition step, while the quartet spin state surface has multiple high-energy barriers that can also lead to various side products including C⁴-aromatic hydroxylation. This work shows that product formation is more feasible on the low spin state, while the physicochemical properties of the substrate govern barrier heights of the rate-determining step of the reaction. Finally, the importance of the second-coordination sphere is highlighted that determines the product distributions and guides the bifurcation pathways.

Can Antioxidants Reduce the Toxicity of Bisphenol?

BPA is still the subject of extensive research due to its widespread use, despite its significant toxicity resulting not only from its negative impact on the endocrine system but also from disrupting the organism’s oxidative homeostasis. At the molecular level, bisphenol A (BPA) causes an increased production of ROS and hence a change in the redox balance, mitochondrial dysfunction, and modulation of cell signaling pathways. Importantly, these changes accumulate in animals and humans, and BPA toxicity may be aggravated by poor diet, metabolic disorders, and coexisting diseases. Accordingly, approaches using antioxidants to counteract the negative effects of BPA are being considered. The preliminary results that are described in this paper are promising, however, it should be emphasized that further studies are required to determine the optimal dosage and treatment regimen to counteract BPA toxicity. It also seems necessary to have a more holistic approach showing, on the one hand, the influence of BPA on the overall human metabolism and, on the other hand, the influence of antioxidants in doses that are acceptable with the diet on BPA toxicity. This is due in part to the fact that in many cases, the positive effect of antioxidants in in vitro studies is not confirmed by clinical studies. For this reason, further research into the molecular mechanisms of BPA activity is also recommended.

Bisphenol F Exposure in Adolescent Heterogeneous Stock Rats Affects Growth and Adiposity

Bisphenol F (BPF) is increasingly substituting bisphenol A in manufacturing polycarbonates and consumer products. The cardiometabolic effects of BPF in either humans or model organisms are not clear, and no studies to date have investigated the role of genetic background on susceptibility to BPF-induced cardiometabolic traits. The primary goal of this project was to determine if BPF exposure influences growth and adiposity in male N:NIH heterogeneous stock (HS) rats, a genetically heterogeneous population. Littermate pairs of male HS rats were randomly exposed to either vehicle (0.1% ethanol) or 1.125 µg/ml BPF in 0.1% ethanol for 5 weeks in drinking water starting at 3 weeks-of-age. Water consumption and body weight was measured weekly, body composition was determined using nuclear magnetic resonance, urine and feces were collected in metabolic cages, and blood and tissues were collected at the end of the study. BPF-exposed rats showed significantly increased body growth and abdominal adiposity, risk factors for cardiometabolic disease. Urine output was increased in BPF-exposed rats, driving a trend in increased creatinine clearance. We also report the first relationship between a bisphenol metabolizing enzyme and a bisphenol-induced phenotype. Preliminary heritability estimates of significant phenotypes suggest that BPF exposure may alter trait variation. These findings support BPF exposure as a cardiometabolic disease risk factor and indicate that the HS rat will be a useful model for dissecting gene by BPF interactions on metabolic health.

Potent Clastogenicity of Bisphenol Compounds in Mammalian Cells-Human CYP1A1 Being a Major Activating Enzyme

Bisphenols (BPs) are environmental pollutants with relevant DNA damage in human population; however, they are generally inactive in standard mutagenicity assays, possibly due to insufficient metabolic activation. In this study, induction of micronuclei and double-strand DNA breaks by BPA, BPF, and BPS in Chinese hamster V79-derived cell lines expressing various human CYP enzymes and a human hepatoma (C3A) (metabolism-proficient) cell line were investigated. Molecular docking of BPs to human CYPs indicated some substrate-enzyme potentials, including CYP1A1 for each compound, which did not induce micronuclei in V79-derived cell lines expressing human CYP1A2, 2E1, or 3A4 but became positive in human CYP1A1-expressing (V79-hCYP1A1) cells. In V79-hCYP1A1 and C3A cells, all compounds induced double-strand DNA breaks and micronuclei formation, which were blocked/significantly attenuated by 1-aminobenzotriazole (CYP inhibitor) or 7-hydroxyflavone (selective CYP1A1 inhibitor). Coexposure of C3A cells to pentachlorophenol (sulfotransferase 1 inhibitor) or ketoconazole (UDP-glucuronosyltransferase 1A inhibitor) potentiated micronuclei induction by each compound, with thresholds lowered from 2.5-5.0 to 0.6-1.2 μM. Immunofluorescence staining of centromere protein B with micronuclei formed in C3A cells by each compound indicated pure clastogenic effects. In conclusion, BPs are potently clastogenic in mammalian cells, which require activation primarily by human CYP1A1 and are negatively modulated by phase II metabolism.

Role of Antioxidants in Alleviating Bisphenol A Toxicity

Bisphenol A (BPA) is an oestrogenic endocrine disruptor widely used in the production of certain plastics, e.g., polycarbonate, hard and clear plastics, and epoxy resins that act as protective coating for food and beverage cans. Human exposure to this chemical is thought to be ubiquitous. BPA alters endocrine function, thereby causing many diseases in human and animals. In the last few decades, studies exploring the mechanism of BPA activity revealed a direct link between BPA-induced oxidative stress and disease pathogenesis. Antioxidants, reducing agents that prevent cellular oxidation reactions, can protect BPA toxicity. Although the important role of antioxidants in minimizing BPA stress has been demonstrated in many studies, a clear consensus on the associated mechanisms is needed, as well as the directives on their efficacy and safety. Herein, considering the distinct biochemical properties of BPA and antioxidants, we provide a framework for understanding how antioxidants alleviate BPA-associated stress. We summarize the current knowledge on the biological function of enzymatic and non-enzymatic antioxidants, and discuss their practical potential as BPA-detoxifying agents.

Effects of prenatal bisphenol A exposure on the hepatic transcriptome and proteome in rat offspring

Developmental exposure to bisphenol A (BPA) is associated with liver dysfunction and diseases in adulthood. The aims of this study were to assess the effects of prenatal BPA exposure on the hepatic transcriptome and proteome in female and male offspring and to understand adverse outcome pathways (AOPs) to observed phenotypic effects. Pregnant Wistar rats were exposed to 50 or 5000 μg BPA/kg bw/day, or 17β-estradiol (E2, 50 μg/kg bw/day) from embryonic day 3 to 18. The liver transcriptome and proteome profiles were analyzed in the newborn (postnatal day 1; PND1) and weaning (PND21) rat offspring. Based on the differentially expressed genes/proteins derived from transcriptome and proteome profiles, we performed pathway, transcription factor, and disease enrichment analyses. A principal component analysis of transcriptome data demonstrated that prenatal BPA exposure caused masculinization of the hepatic transcriptome in females. Both of transcriptomic and proteomic data showed that prenatal BPA exposure led to the disruption of cell cycle, lipid homeostasis, and hormone balance in offspring. Most of the effects at the transcript level were extended from newborn to weaning in males, but were moderated until weaning in females. The alterations at the transcript and protein levels were accordant with the observation of increases in body weight and anogenital distance and changes in hepatosomatic index in the offspring. Collectively, we constructed AOPs with evidence of sex- and age-specific actions of prenatal BPA exposure in the offspring.

Bisphenol-A in the European Prospective Investigation into Cancer and Nutrition cohort in Spain: Levels at recruitment and associated dietary factors

Bisphenol A (BPA) is considered an endocrine disruptor and it is present in numerous products of daily use. The aim of this study was to analyze serum BPA concentrations in a subcohort of the Spanish European Prospective Investigation into Cancer and Nutrition (EPIC), as well as to identify potential predictors of the exposure. The population consisted on 3553 subjects from 4 EPIC-Spain centres and BPA levels were measured in serum samples by UHPLC-MS/MS. Almost 70% of the participants showed detectable BPA values (>0.2 ng/ml), with a geometric mean of 1.19 ng/ml (95% CI: 1.12-1.25). By sex, detectable percentages were similar (p = 0.56) but with higher serum levels in men (1.27 vs 1.11 ng/ml, p = 0.01). Based on the adjusted regression models, a 50 g/day increase in the consumption of added fats and oils were associated with 43% lower BPA serum levels, while sugar and confectionary was associated with 25% higher levels of serum BPA. We evidenced differential exposure levels by province, sex and age, but not by anthropometric or lifestyle characteristics. Further investigation is needed to understand the influence of diet in BPA exposure.

Ginger extract ameliorates bisphenol A (BPA)-induced disruption in thyroid hormones synthesis and metabolism: Involvement of Nrf-2/HO-1 pathway

Environmental exposure to BPA is alarming because of the potential health threats for example those concerning the thyroid glands which may show signs of oxidative stress. This original study aimed to investigate the possible antioxidant protective effects of ginger extract (GE) against BPA-induced thyroid injury in male rats, focusing on its effect on Nrf-2/HO-1 signaling and thyroid hormone synthesis regulating genes. The cascade of events in thyroid injury induced by chronic exposure to BPA (200 mg/kg b.w/day for 35 days) involved a preliminary overproduction of ROS followed by significant (p ≤ 0.05) depletion of reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity as well as significant increases of malondialdehyde (MDA) contents, myeloperoxidase (MPO) activity and inducible nitric oxide synthase (iNOS) gene expression. These actions consequently down-regulate the Nrf-2/HO-I signaling which eventually resulting in the DNA fragmentation within the thyroid tissues. Moreover, BPA administration caused a reduction of thyroid iodide uptake evidenced by significant inhibitions (p ≤ 0.05) of sodium-iodide symporter (NIS), thyroid peroxidase (TPO) and thyroid-stimulating hormone receptor (TSHR) mRNA expressions within the thyroid glands. A subsequent significant decreased serum levels of T3 and T4 accompanied by a significantly increased serum TSH level were also detected. These findings were confirmed by the severe pathological changes detected in the thyroid tissue of BPA treated rats. These biochemical and histological alterations were significantly alleviated with ginger administration (250 mg/kg b.w/day for 35 days) plus BPA. In conclusion, ginger extract is a potent antioxidant that can effectively protect against BPA-induced thyroid oxidative damage by activating the Nrf-2/HO-1 gene expressions and enhancing the thyroid hormones synthesis. This is the first study to show the contribution of Nrf-2/HO-1 pathway to the protective effect of ginger extract against BPA-induced thyroid oxidative damage and thyroid hormonal disruption.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Endocrine disruptors of inhibiting testicular 3β-hydroxysteroid dehydrogenase

Testicular 3β-hydroxysteroid dehydrogenase (HSD3B) is a steroidogenic enzyme, catalyzing the conversion of 3β-hydroxysteroids into 3-keto-steroids. Two distinct isoforms in the human are cloned, HSD3B1 and HSD3B2, and HSD3B2 is located in the testis. HSD3B2 is a two-substrate enzyme, which binds to cofactor NAD⁺ and a 3β-steroid. Many endocrine disruptors, including industrial compounds (phthalates, bisphenols, and perfluoroalkyl substances), insecticides and biocides (organochlorine insecticides and organotins), food additives (butylated hydroxyanisole, resveratrol, gossypol, flavones, and isoflavones), and drugs (etomidate, troglitazone, medroxyprogesterone acetate, and ketoconazole) inhibit testicular HSD3B, possibly interfering with androgen synthesis. In this review, we discuss the distinct testicular isoform of HSD3B, its gene, chemistry, subcellular location, and the endocrine disruptors that directly inhibit testicular HSD3B and their inhibitory modes.

Hepatic Detoxification of Bisphenol A is Retinoid-Dependent

Bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl) propane) is a widely used industrial chemical. The extensive distribution of BPA in the environment poses risks to humans. However, the molecular mechanisms underlying BPA toxicity as well as its effective detoxification and elimination are not well understood. We have investigated specifically for BPA the notion raised in the literature that the optimal sensing, detoxification, and elimination of xenobiotics requires retinoid (natural derivatives and synthetic analogs of vitamin A) actions. The objective of the study was to explore how retinoids, both those stored in the liver and those originating from recent oral intake, help maintain an optimal xenobiotic detoxification response, affecting mRNA expression and activities of elements of xenobiotic detoxification system upon BPA administration to mice. Wild-type and mice lacking hepatic retinoid stores (Lrat-/-) were acutely treated with BPA (50 mg/kg body weight), with or without oral supplementation with retinyl acetate. Hepatic mRNA expression levels of the genes encoding nuclear receptors and their downstream targets involved in xenobiotic biotransformation, phase I and phase II enzyme activities, and levels of oxidative damage to cellular proteins and lipids in hepatic microsomes, mitochondria and cytosol, were assessed. BPA treatment induced hepatic activities needed for its detoxification and elimination in wild-type mice. However, BPA failed to induce these activities in the livers of Lrat-/- mice. Oral supplementation with retinyl acetate restored phase I and phase II enzyme activities, but accelerated BPA-induced oxidative damage through enhancement of non-mitochondrial ROS production. Thus, the activities of the enzymes involved in the hepatic elimination of BPA require hepatic retinoid stores. The extent of hepatic damage that arises from acute BPA intoxication is directly affected by retinoid administration during the period of BPA exposure and hepatic retinoid stores that have accumulated over the lifetime of the organism.

Bisphenol a increases risk for presumed non-alcoholic fatty liver disease in Hispanic adolescents in NHANES 2003-2010

BACKGROUND

Bisphenol-A (BPA) is a ubiquitous chemical and recognized endocrine disruptor associated with obesity and related disorders. We explored the association between BPA levels and suspected non-alcoholic fatty liver disease (NAFLD).

METHODS

Unweighted analyses were used to study the relationship between urinary BPA levels and suspected NAFLD (alanine aminotransferase (ALT). > 30 U/L, body mass index (BMI) Z-score > 1.064 and evidence of insulin resistance) using National Health and Nutrition Examination Survey (NHANES) data (2003-2010) on 12-19 year olds. Unweighted and weighted analyses were used to evaluate the risk with only elevated ALT.

RESULTS

We included 944 adolescents with urinary BPA and fasting laboratory tests from a total of 7168 adolescents. Risk of suspected NAFLD was increased in the second quartile of BPA levels (1.4-2.7 ng/mL) when compared to the first (< 1.4 ng/mL) (Odds Ratio (OR) 4.23, 95% Confidence Interval (CI) 1.44-12.41). The ORs for the third and second quartiles were positive but did not reach statistical significance. The association was stronger in Hispanics (n = 344) with BPA levels in the second (OR 6.12, 95% C.I. 1.62-23.15) quartile and when limiting the analyses to overweight/obese adolescents (n = 332), in the second (OR 5.56, 95% C.I. 1.28-24.06) and fourth BPA quartiles (OR 6.85, 95% C.I. 1.02-46.22) compared to the first quartile. BPA levels were not associated with ALT elevation.

CONCLUSIONS

The risk of suspected NAFLD is increased in participants in higher quartiles of BPA exposure, particularly in those of Hispanic ethnicity. Further studies are required to fully understand the potential role of BPA in non-alcoholic fatty liver disease.

Perinatal Bisphenol A Exposure Induces Chronic Inflammation in Rabbit Offspring via Modulation of Gut Bacteria and Their Metabolites

Emerging evidence suggests that environmental toxicants may influence inflammation-promoted chronic disease susceptibility during early life. BPA, an environmental endocrine disruptor, can transfer across the placenta and accumulate in fetal gut and liver. However, underlying mechanisms for BPA-induced colonic and liver inflammation are not fully elucidated. In this report, we show how perinatal BPA exposure in rabbits alters gut microbiota and their metabolite profiles, which leads to colonic and liver inflammation as well as to increased gut permeability as measured by elevated serum lipopolysaccharide (LPS) levels in the offspring. Also, perinatal BPA exposure leads to reduced levels of gut bacterial diversity and bacterial metabolites (short-chain fatty acids [SCFA]) and elevated gut permeability—three common early biomarkers of inflammation-promoted chronic diseases. In addition, we showed that SCFA ameliorated BPA-induced intestinal permeability in vitro. Thus, our study results suggest that correcting environmental toxicant-induced bacterial dysbiosis early in life may reduce the risk of chronic diseases later in life.

Bisphenol A (BPA) accumulates in the maturing gut and liver in utero and is known to alter gut bacterial profiles in offspring. Gut bacterial dysbiosis may contribute to chronic colonic and systemic inflammation. We hypothesized that perinatal BPA exposure-induced intestinal (and liver) inflammation in offspring is due to alterations in the microbiome and colonic metabolome. The 16S rRNA amplicon sequencing analysis revealed differences in beta diversity with a significant reduction in the relative abundances of short-chain fatty acid (SCFA) producers such as Oscillospira and Ruminococcaceae due to BPA exposure. Furthermore, BPA exposure reduced fecal SCFA levels and increased systemic lipopolysaccharide (LPS) levels. BPA exposure-increased intestinal permeability was ameliorated by the addition of SCFA in vitro. Metabolic fingerprints revealed alterations in global metabolism and amino acid metabolism. Thus, our findings indicate that perinatal BPA exposure may cause gut bacterial dysbiosis and altered metabolite profiles, particularly SCFA profiles, leading to chronic colon and liver inflammation.

IMPORTANCE Emerging evidence suggests that environmental toxicants may influence inflammation-promoted chronic disease susceptibility during early life. BPA, an environmental endocrine disruptor, can transfer across the placenta and accumulate in fetal gut and liver. However, underlying mechanisms for BPA-induced colonic and liver inflammation are not fully elucidated. In this report, we show how perinatal BPA exposure in rabbits alters gut microbiota and their metabolite profiles, which leads to colonic and liver inflammation as well as to increased gut permeability as measured by elevated serum lipopolysaccharide (LPS) levels in the offspring. Also, perinatal BPA exposure leads to reduced levels of gut bacterial diversity and bacterial metabolites (short-chain fatty acids [SCFA]) and elevated gut permeability—three common early biomarkers of inflammation-promoted chronic diseases. In addition, we showed that SCFA ameliorated BPA-induced intestinal permeability in vitro. Thus, our study results suggest that correcting environmental toxicant-induced bacterial dysbiosis early in life may reduce the risk of chronic diseases later in life.

Bisphenol a induces steatosis in HepaRG cells using a model of perinatal exposure

Human exposure to bisphenol A (BPA) could favor obesity and related metabolic disorders such as hepatic steatosis. Investigations in rodents have shown that these deleterious effects are observed not only when BPA is administered during the adult life but also with different protocols of perinatal exposure. Whether perinatal BPA exposure could pose a risk in human is currently unknown, and thus appropriate in vitro models could be important to tackle this major issue. Accordingly, we determined whether long-term BPA treatment could induce steatosis in human HepaRG cells by using a protocol mimicking perinatal exposure. To this end, the kinetics of expression of seven proteins differentially expressed during liver development was determined during a 4-week period of cell culture required for proliferation and differentiation. By analogy with data reported in rodents and humans, our results indicated that the period of cell culture around day 15 and day 18 after seeding could be considered as the "natal" period. Consequently, HepaRG cells were treated for 3 weeks with BPA (from 0.2 to 2000 nM), with a treatment starting during the proliferating period. BPA was able to induce steatosis with a nonmonotonic dose response profile, with significant effects on neutral lipids and triglycerides observed for the 2 nM concentration. However, the expression of many enzymes involved in lipid and carbohydrate homeostasis was unchanged in exposed HepaRG cells. The expression of other potential BPA targets and enzymes involved in BPA biotransformation was also determined, giving answers as well as new questions regarding the mechanisms of action of BPA. Hence, HepaRG cells provide a valuable model that can prove useful for the toxicological assessment of endocrine disruptors on hepatic metabolisms, in particular in the developing liver. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1024-1036, 2017.

The Association of Serum Bisphenol A with Thyroid Autoimmunity

Introduction: Data on the association of bisphenol A (BPA) exposure and autoimmunity in humans is unclear. Objective: To elucidate the influence of BPA on thyroid autoimmunity, in the present study we assessed the association between serum BPA and thyroid autoantibodies. Methods: Serum samples from 2361 subjects, aged ≥15 years, from the Thai 4th National Health Examination Survey were measured for BPA, antithyroglobulin (TgAb), antithyroperoxidase (TPOAb) and antithyrotrophin receptor (TRAb) antibodies. Results: The proportion of subjects positive for TgAb, TPOAb and TRAb were 11.1%, 14.9% and 1.9%, respectively. With regard to BPA, 51.9% had serum BPA levels exceeding the detection limit of the assay (0.3). There was a significant increasing trend for subjects with TgAb (p < 0.05) and TPOAb (p < 0.001) positivity as BPA quartiles increased, particularly in the highest quartile. In contrast, no relationship between BPA quartiles and TRAb was found. Logistic regression analysis showed that age, gender and BPA quartiles were determinants of TPOAb or TgAb positivity, independent of BMI. However, only the association between BPA and TPOAb positivity was consistent in both men and women. Conclusions: BPA was independently associated with TPOAb positivity. However, its mechanism related to TPOAb positivity, subsequently leading to autoimmune thyroid disease, needs further investigation.

Bisphenol A and its analogs: Do their metabolites have endocrine activity?

Structural analogs of bisphenol A are commonly used as its alternatives in industrial and commercial applications. Nevertheless, the question arises whether the use of other bisphenols is justified as replacements for bisphenol A in mass production of plastic materials. To evaluate the influence of metabolic reactions on endocrine activities of bisphenols, we conducted a systematic review of the literature. Knowledge about the metabolic pathways and enzymes involved in metabolic biotransformations is essential for understanding and predicting mechanisms of toxicity. Bisphenols are metabolized predominantly by the glucuronidation reaction, which is considered their most important detoxification pathway, as based on current knowledge, glucuronides do not have activity on endocrine receptors. In contrast, several oxidative metabolites of bisphenols with enhanced endocrine activities are presented, and these findings indicate that oxidative metabolites of bisphenols can still have endocrine activities in humans.

Influence of metabolism on endocrine activities of bisphenol S

Bisphenol S (BPS; bis[4-hydroxyphenyl]sulfone) is commonly used as a replacement for bisphenol A in numerous consumer products. The main goal of this study was to examine the influence of different metabolic reactions that BPS undergoes on the endocrine activity. We demonstrate that hydroxylation of the aromatic ring of BPS, catalyzed mainly by the cytochrome P450 enzymes CYP3A4 and CYP2C9, is its major in-vitro phase I biotransformation. Nevertheless, coupled oxidative-conjugative reactions analyses revealed that glucuronidation and formation of BPS glucuronide is the predominant BPS metabolic pathway. BPS reactive metabolites that can be tracked as glutathione conjugates were not detected in the present study. Two in-vitro systems were used to evaluate the endocrine activity of BPS and its two main metabolites, BPS glucuronide and hydroxylated BPS 4-(4-hydroxy-benzenesulfonyl)-benzene-1,2-diol (BPSM1). In addition, we have tested two structural analogs of BPS, bis[4-(2-hydroxyetoxy)phenyl]sulfone (BHEPS) and 4,4-sulfonylbis(2-methylphenol) (dBPS). The test systems were yeast cells, for evaluating estrogenic and androgenic activities, and the GH3.TRE-Luc reporter cell line for measuring thyroid hormone activity. BPS and BPSM1 were weak agonists of the estrogen receptor, EC50 values of 8.4 × 10(-5) M and 6.7 × 10(-4) M, respectively. Additionally, BPSM1 exhibited weak antagonistic activity toward the thyroid hormone receptor, with an IC50 of 4.3 × 10(-5) M. In contrast to BPSM1, BPS glucuronide was inactive in these assays, inhibiting neither the estrogen nor the thyroid hormone receptors. Hence, glucuronidation appears to be the most important pathway for both BPS metabolism and detoxification.

Bisphenol A and hormone-associated cancers: current progress and perspectives

Bisphenol A (BPA), a carbon-based synthetic compound, exhibits hormone-like properties and is present ubiquitously in the environment and in human tissues due to its widespread use and biological accumulation. BPA can mimic estrogen to interact with estrogen receptors α and β, leading to changes in cell proliferation, apoptosis, or migration and thereby, contributing to cancer development and progression. At the genetic level, BPA has been shown to be involved in multiple oncogenic signaling pathways, such as the STAT3, MAPK, and PI3K/AKT pathways. Moreover, BPA may also interact with other steroid receptors (such as androgen receptor) and plays a role in prostate cancer development. This review summarizes the current literature regarding human exposure to BPA, the endocrine-disrupting effects of BPA, and the role of BPA in hormone-associated cancers of the breast, ovary, and prostate.

Adverse effects of bisphenol A on male reproductive function

BPA is a ubiquitous environmental contaminant, resulting mainly from manufacturing,use or disposal of plastics of which it is a component, and the degradation of industrial plastic-related wastes. Growing evidence from research on laboratory animals, wildlife, and humans supports the view that BPA produces an endocrine disrupting effect and adversely affects male reproductive function. To better understand the adverse effects caused by exposure to BPA, we performed an up-to-date literature review on the topic, with particular emphasis on in utero exposure, and associated effects on spermatogenesis, steroidogenesis, and accessory organs.BPA studies on experimental animals show that effects are generally more detrimental during in utero exposure, a critical developmental stage for the embryo. BPA has been found to produce several defects in the embryo, such as feminization of male fetuses, atrophy of the testes and epididymides, increased prostate size, shortening of AGD, disruption of BTB, and alteration of adult sperm parameters (e.g.,sperm count, motility, and density). BPA also affects embryo thyroid development.During the postnatal and pubertal periods and adulthood, BPA affects the hypothalamic-pituitary-testicular axis by modulating hormone (e.g., LH and FSH,androgen and estrogen) synthesis, expression and function of respective receptors(ER, AR). These effects alter sperm parameters. BPA also induces oxidative stress in the testis and epididymis, by inhibiting antioxidant enzymes and stimulating lipid peroxidation. This suggests that employing antioxidants may be a promising strategy to relieve BPA-induced disturbances.Epidemiological studies have also provided data indicating that BPA alters male reproductive function in humans. These investigations revealed that men occupationally exposed to BPA had high blood/urinary BPA levels, and abnormal semen parameters. BPA-exposed men also showed reduced libido and erectile ejaculatory difficulties; moreover, the overall BPA effects on male reproduction appear to be more harmful if exposure occurs in utero. The regulation of BPA and BPA-related products should be reinforced, particularly where exposure during the fetal period can occur. The current TDI for BPA is proposed as 25 and 50 1-1g/kg bwt/day (European Food Safety Authority and Health Canada, respectively). Based on the evidence available, we believe that a TDI value of 5 1-1g/kg bwt/day is more appropriate (the endpoint is modulation of rat testicular function). Certain BPA derivatives are being considered as alternatives to BPA. However, certain of these related products display adverse effects that are similar to those of BPA. These effects should be carefully considered before using them as final alternatives to BPA in plastic production.

Biotransformation of bisphenol AF to its major glucuronide metabolite reduces estrogenic activity

Bisphenol AF (BPAF), an endocrine disrupting chemical, can induce estrogenic activity through binding to estrogen receptor (ER). However, the metabolism of BPAF in vivo and the estrogenic activity of its metabolites remain unknown. In the present study, we identified four metabolites including BPAF diglucuronide, BPAF glucuronide (BPAF-G), BPAF glucuronide dehydrated and BPAF sulfate in the urine of Sprague-Dawley (SD) rats. BPAF-G was further characterized by nuclear magnetic resonance (NMR). After treatment with a single dose of BPAF, BPAF was metabolized rapidly to BPAF-G, as detected in the plasma of SD rats. Biotransformation of BPAF to BPAF-G was confirmed with human liver microsomes (HLM), and V_max of glucuronidation for HLM was 11.6 nmol/min/mg. We also found that BPAF glucuronidation could be mediated through several human recombinant UDP-glucuronosyltransferases (UGTs) including UGT1A1, UGT1A3, UGT1A8, UGT1A9, UGT2B4, UGT2B7, UGT2B15 and UGT2B17, among which UGT2B7 showed the highest efficiency of glucuronidation. To explain the biological function of BPAF biotransformation, the estrogenic activities of BPAF and BPAF-G were evaluated in ER-positive breast cancer T47D and MCF7 cells. BPAF significantly stimulates ER-regulated gene expression and cell proliferation at the dose of 100 nM and 1 μM in breast cancer cells. However, BPAF-G did not show any induction of estrogenic activity at the same dosages, implying that formation of BPAF-G is a potential host defense mechanism against BPAF. Based on our study, biotransformation of BPAF to BPAF-G can eliminate BPAF-induced estrogenic activity, which is therefore considered as reducing the potential threat to human beings.

Bioactivation of bisphenol A and its analogs (BPF, BPAF, BPZ and DMBPA) in human liver microsomes

Bisphenol A analogs are a class of chemicals known as diphenylmethanes, which contain two benzene rings separated by one central carbon atom, usually with a para-hydroxy group on both benzene rings. Bisphenol A (BPA) can induce an uterotrophic response in immature CD-1 mice and elicits estrogenic responses in many other experimental systems. Besides highlighting endocrine effects, a number of metabolic studies provide strong support for the idea that reactive species of BPA are formed in vitro and in vivo that can form covalent adducts with nucleophilic macromolecules and/or produce oxidative stress. We used a liquid chromatography with a triple quadrupole tandem mass spectrometry (LC-MS/MS) for the detection of metabolites and glutathione conjugates of BPA and its analogs (BPF, BPAF, BPZ and DMBPA) in human liver microsomes (HLM) or with recombinant CYP isozymes in the presence of NADPH and GSH as a trapping agent. We have confirmed that BPA and its structural analogs form hydroxylated metabolites and electrophilic species during bioactivation in HLM and CYP isozymes. These results provided important mechanistic insight into the metabolic fate of BPA structural analogs in vitro.

Inhibitors of testosterone biosynthetic and metabolic activation enzymes

The Leydig cells of the testis have the capacity to biosynthesize testosterone from cholesterol. Testosterone and its metabolically activated product dihydrotestosterone are critical for the development of male reproductive system and spermatogenesis. At least four steroidogenic enzymes are involved in testosterone biosynthesis: Cholesterol side chain cleavage enzyme (CYP11A1) for the conversion of cholesterol into pregnenolone within the mitochondria, 3β-hydroxysteroid dehydrogenase (HSD3B), for the conversion of pregnenolone into progesterone, 17α-hydroxylase/17,20-lyase (CYP17A1) for the conversion of progesterone into androstenedione and 17β-hydroxysteroid dehydrogenase (HSD17B3) for the formation of testosterone from androstenedione. Testosterone is also metabolically activated into more potent androgen dihydrotestosterone by two isoforms 5α-reductase 1 (SRD5A1) and 2 (SRD5A2) in Leydig cells and peripheral tissues. Many endocrine disruptors act as antiandrogens via directly inhibiting one or more enzymes for testosterone biosynthesis and metabolic activation. These chemicals include industrial materials (perfluoroalkyl compounds, phthalates, bisphenol A and benzophenone) and pesticides/biocides (methoxychlor, organotins, 1,2-dibromo-3-chloropropane and prochloraz) and plant constituents (genistein and gossypol). This paper reviews these endocrine disruptors targeting steroidogenic enzymes.

CYP17 inhibitors for prostate cancer therapy

Prostate cancer (PC) is now the second most prevalent cause of death in men in the USA and Europe. At present, the major treatment options include surgical or medical castration. These strategies cause ablation of the production of testosterone (T), dihydrotestosterone (DHT) and related androgens by the testes. However, because these procedures do not affect adrenal, prostate and other tissues' androgen production, they are often combined with androgen receptor antagonists to block their action. Indeed, recent studies have unequivocally established that in castration-resistant prostate cancer (CRPC) many androgen-regulated genes become re-expressed and tissue androgen levels increase despite low serum levels. Clearly, inhibition of the key enzyme which catalyzes the biosynthesis of androgens from pregnane precursors, 17α-hydroxy/17,20-lyase (hereafter referred to as CYP17) could prevent androgen production from all sources. Thus, total ablation of androgen production by potent CYP17 inhibitors may provide effective treatment of prostate cancer patients. This review highlights the role of androgen biosynthesis in the progression of prostate cancer and the impact of CYP17 inhibitors, such as ketoconazole, abiraterone acetate, VN/124-1 (TOK-001) and TAK-700 in the clinic and in clinical development. Article from the special issue on Targeted Inhibitors.

Ipso substitution of bisphenol A catalyzed by microsomal cytochrome P450 and enhancement of estrogenic activity

Bisphenol A (BPA), an industrial chemical with estrogenic activity, was investigated as a substrate for the ipso-metabolism catalyzed by microsomal cytochrome P450 (P450). BPA was expected to be transformed to a quinol via an ipso-addition reaction; however, hydroquinone (HQ) was detected as a metabolite via an ipso-substitution reaction. Isopropenylphenol (IPP) and hydroxycumyl alcohol (HCA) were also produced as eliminated metabolites by C-C bond scission via ipso-substitution. Incorporation of the ¹⁸O atom to HCA from H₂¹⁸O suggested the presence of a carbocation intermediate. Bulkiness of p-substituted group of BPA and/or stability of the eliminated carbocation intermediate may cause ipso-substitution of BPA. CYP3A4 and CYP3A5 showed higher activity for ipso-substitution. CYP2D6*1 also showed the activity; however, the other 9 isozymes did not. IPP showed ER-binding activity in the same degree of BPA. Furthermore, the ER-binding activity of HCA was about a hundred times greater than that of BPA. These results suggested that this new metabolic pathway contributes to the activation of the estrogenic activity of BPA.

Defined plant extracts can protect human cells against combined xenobiotic effects

Background

Pollutants representative of common environmental contaminants induce intracellular toxicity in human cells, which is generally amplified in combinations. We wanted to test the common pathways of intoxication and detoxification in human embryonic and liver cell lines. We used various pollutants such as Roundup residues, Bisphenol-A and Atrazine, and five precise medicinal plant extracts called Circ1, Dig1, Dig2, Sp1, and Uro1 in order to understand whether specific molecular actions took place or not.

Methods

Kidney and liver are major detoxification organs. We have studied embryonic kidney and hepatic human cell lines E293 and HepG2. The intoxication was induced on the one hand by a formulation of one of the most common herbicides worldwide, Roundup 450 GT+ (glyphosate and specific adjuvants), and on the other hand by a mixture of Bisphenol-A and Atrazine, all found in surface waters, feed and food. The prevention and curative effects of plant extracts were also measured on mitochondrial succinate dehydrogenase activity, on the entry of radiolabelled glyphosate (in Roundup) in cells, and on cytochromes P450 1A2 and 3A4 as well as glutathione-S-transferase.

Results

Clear toxicities of pollutants were observed on both cell lines at very low sub-agricultural dilutions. The prevention of such phenomena took place within 48 h with the plant extracts tested, with success rates ranging between 25-34% for the E293 intoxicated by Roundup, and surprisingly up to 71% for the HepG2. By contrast, after intoxication, no plant extract was capable of restoring E293 viability within 48 h, however, two medicinal plant combinations did restore the Bisphenol-A/Atrazine intoxicated HepG2 up to 24-28%. The analysis of underlying mechanisms revealed that plant extracts were not capable of preventing radiolabelled glyphosate from entering cells; however Dig2 did restore the CYP1A2 activity disrupted by Roundup, and had only a mild preventive effect on the CYP3A4, and no effect on the glutathione S-transferase.

Conclusions

Environmental pollutants have intracellular effects that can be prevented, or cured in part, by precise medicinal plant extracts in two human cell lines. This appears to be mediated at least in part by the cytochromes P450 modulation.

Transmembrane transports of acrylamide and bisphenol A and effects on development of zebrafish (Danio rerio)

Acrylamide (AA) and bisphenol A (BPA) are two kinds of pollutants with different structures and polarities. AA found in fried and toasted starchy foods can cause developmental and reproductive toxicity and BPA has neuro-, immuno- and developmental toxicities. Their transports in zebrafish (Danio rerio) embryos were determined and their toxicity characteristics observed. Approximately 70% of AA was concentrated on the outer membrane surface probably via hydrogen bonds and van der Waals forces, but only 0.3% of AA entered the cytoplasm. In contrast, over 10% of the BPA adsorbed to the cells entered the cytoplasm via the membrane by lipid-water partition. The hydrophilic AA and hydrophobic BPA used different cell transport pathways; AA accumulated on the outer membrane surface whereas BPA readily reached the cytoplasm. AA caused acute and indirect toxicity in developing cells, including serious malnutrition and axial malformation. BPA caused chemical damage to developing cells by causing pericardial edema. The antagonistic effect of the AA/BPA mixture's combinational toxicity to embryos was found and explained by the accumulation of AA on the out surface of membrane inhibiting the transfer of BPA to the cytoplasm.

Binding of bisphenol A and acrylamide to BSA and DNA: insights into the comparative interactions of harmful chemicals with functional biomacromolecules

The interactions between bisphenol A (BPA)/acrylamide (AA) and bovine serum albumin (BSA)/deoxyribonucleic acid (DNA) was investigated by the equilibrium dialysis, fluorophotometry, isothermal titration calorimetry (ITC) and circular dichroism (CD). The bindings of BPA and AA to BSA and DNA responded to the partition law and Langmuir isothermal model, respectively. The saturation mole number of AA was calculated to be 24 per mol BSA and 0.26 per mol DNA-P. All the reactions were spontaneous driven by entropy change. BPA stacked into the aromatic hydrocarbon groups of BSA and between adjacent basepairs of DNA via the hydrophobic effect. The interactions of AA with BSA and DNA induced the formation of hydrogen bond and caused changes of their secondary structures. At normal physiological condition, 0.100 mmol/l BPA reduced the binding of vitamin B(2) to BSA by more than 70%, and 2.8 mmol/l AA by almost one half. This work provides an insight into non-covalent intermolecular interaction between organic contaminant and biomolecule, helping to elucidate the toxic mechanism of harmful chemicals.

Dietary phytochemicals regulate whole-body CYP1A1 expression through an arylhydrocarbon receptor nuclear translocator-dependent system in gut

Cytochrome P450 1A1 (CYP1A1) is one of the most important detoxification enzymes due to its broad substrate specificity and wide distribution throughout the body. On the other hand, CYP1A1 can also produce highly carcinogenic intermediate metabolites through oxidation of polycyclic aromatic hydrocarbons. We describe what we believe to be a novel regulatory system for whole-body CYP1A1 expression by a factor originating in the gut. A mutant mouse was generated in which the arylhydrocarbon receptor nuclear translocator (Arnt) gene is disrupted predominantly in the gut epithelium. Surprisingly, CYP1A1 mRNA expression and enzymatic activities were markedly elevated in almost all non-gut tissues in this mouse line. The induction was even observed in early-stage embryos in pregnant mutant females. Interestingly, the upregulation was CYP1A1 selective and lost upon administration of a synthetic purified diet. Moreover, the increase was recovered by addition of the natural phytochemical indole-3-carbinol to the purified diet. These results suggest that an Arnt-dependent pathway in gut has an important role in regulation of the metabolism of dietary CYP1A1 inducers and whole-body CYP1A1 expression. This machinery might be involved in naturally occurring carcinogenic processes and/or other numerous biological responses mediated by CYP1A1 activity.

Large effects from small exposures. III. Endocrine mechanisms mediating effects of bisphenol A at levels of human exposure

Over 6 billion pounds per year of the estrogenic monomer bisphenol A (BPA) are used to manufacture polycarbonate plastic products, in resins lining metal cans, in dental sealants, and in blends with other types of plastic products. The ester bond linking BPA molecules in polycarbonate and resins undergoes hydrolysis, resulting in the release of free BPA into food, beverages, and the environment, and numerous monitoring studies now show almost ubiquitous human exposure to biologically active levels of this chemical. BPA exerts estrogenic effects through the classical nuclear estrogen receptors, and BPA acts as a selective estrogen receptor modulator. However, BPA also initiates rapid responses via estrogen receptors presumably associated with the plasma membrane. Similar to estradiol, BPA causes changes in some cell functions at concentrations between 1 pM and 1 nM, and the mean and median range of unconjugated BPA measured by multiple techniques in human pregnant maternal, fetal, and adult blood and other tissues exceeds these levels. In contrast to these published findings, BPA manufacturers persist in describing BPA as a weak estrogen and insist there is little concern with human exposure levels. Our concern with human exposure to BPA derives from 1) identification of molecular mechanisms mediating effects in human and animal tissues at very low doses, 2) in vivo effects in experimental animals caused by low doses within the range of human exposure, and 3) widespread human exposure to levels of BPA that cause adverse effects in animals.

Bisphenol A binds to protein disulfide isomerase and inhibits its enzymatic and hormone-binding activities

Bisphenol A [2,2-bis-(4-hydroxyphenyl) propane; BPA] is a versatile industrial material for plastic products, but is increasingly being recognized as a pervasive industrial pollutant as well. Accumulating evidence indicates that the environmental contaminant BPA is one of the endocrine-disrupting chemicals that potentially can adversely affect humans as well as wildlife. To define the molecular aspects of BPA action, we first investigated the molecules with which it physically interacts. High BPA-binding activity was detected in the P2 membrane fraction prepared from rat brains. As determined by SDS-PAGE analysis, the molecular mass of a BPA-binding protein purified from the rat brain P2 fraction was 53 kDa. The N-terminal amino acid sequence of the purified BPA-binding protein was identical with that of the rat protein disulfide isomerase (PDI), which is a multifunctional protein that is critically involved in the folding, assembly, and shedding of many cellular proteins via its isomerase activity in addition to being considered to function as an intracellular hormone reservoir. The Kd value of BPA binding to recombinant rat PDI was 22.6 +/- 6.6 microm. Importantly, the binding activity of L-T3 and 17beta-estradiol hormones to PDI was competitively inhibited by BPA in addition to abolishing its isomerase activities. In this paper we report that the ubiquitous and multifunctional protein PDI is a target of BPA and propose that binding to PDI and subsequent inhibition of PDI activity might be mechanistically responsible for various actions of BPA.

Effects of bisphenol A-related diphenylalkanes on vitellogenin production in male carp (Cyprinus carpio) hepatocytes and aromatase (CYP19) activity in human H295r adrenocortical carcinoma cells

The present study investigated the effects of the known xenoestrogen bisphenol A (BPA) relative to eight BPA-related diphenylalkanes on estrogen receptor (ER)-mediated vitellogenin (vtg) production in hepatocytes from male carp (Cyprinus carpio), and on aromatase (CYP19) activity in the human adrenocortical H295R carcinoma cell line. Of the eight diphenylalkanes, only 4,4'-(hexafluoropropylidene)diphenol (BHF) and 2,2'-bis(4-hydroxy-3-methylphenyl)propane (BPRO) induced vtg, i.e., to a maximum of 3% to 4% (at 100 microM) compared with 8% for BPA relative to the maximum induction by 17beta-estradiol (E2, 1 microM). Bisphenol A diglycidyl ether (BADGE) was a potent antagonist of vtg production with an IC50 of 5.5 microM, virtually 100% inhibition of vtg at 20 microM, and an inhibitive (IC50) potency about one-tenth that of the known ER antagonist tamoxifen (IC50, 0.6 microM). 2,2'-Diallyl bisphenol A, 4,4'-(1,4-phenylene-diisopropylidene)bisphenol, BPRO, and BHF were much less inhibitory with IC50 concentrations of 20-70 microM, and relative potencies of 0.03 and 0.009 with tamoxifen. Bisphenol ethoxylate showed no anti-estrogenicity (up to 100 microM), and 4,4'-isopropylidene-diphenol diacetate was only antagonistic at 100 microM. When comparing the (anti)estrogenic potencies of these bisphenol A analogues/diphenylalkanes, anti-estrogenicity occurred at lower concentrations than estrogenicity. 4,4'-Isopropylidenebis(2,6-dimethylphenol) (IC50, 2.0 microM) reduced E2-induced (EC50, 100 nM) vtg production due to concentration-dependent cytotoxicity as indicated by a parallel decrease in MTT activity and vtg, whereas the remaining diphenylalkanes did not cause any cytotoxicity relative to controls. None of the diphenylalkanes (up to 100 microM) induced EROD activity indicating that concentration-dependent, CYP1A enzyme-mediated metabolism of E2, or any Ah-receptor-mediated interaction with the ER, was not a likely explanation for the observed anti-estrogenic effects. At concentrations as great as 100 microM, none of the diphenylalkanes directly inhibited aromatase (CYP19) activity in H295R cells. Environmental exposure of fish to BPA and related diphenylalkanes, depending on the structure, may pose anti-estrogenic, and to a lesser extent estrogenic, risks to development and reproduction.

Herbicide resistance in transgenic plants with mammalian P450 monooxygenase genes

Transgenic potato and rice plants were generated by the introduction of human P450 species, CYP1A1, CYP2B6, CYP2C9 and CYP2C19, which metabolized a number of herbicides, insecticides and industrial chemicals. The transgenic potato plant T1977 co-expressing CYP1A1, CYP2B6 and CYP2C19 genes showed remarkable cross-resistance to several herbicides with different structures and modes of action due to metabolism of these herbicides by the P450 species expressed. The transgenic rice plant 2C9-57R2 expressing CYP2C9 gene showed resistance to sulfonylureas, and the transgenic rice plant 2C19-12R1 expressing CYP2C19 gene showed cross-resistance to certain herbicides with different structures and modes of action. These transgenic plants appear to be useful for herbicide resistance as well as phytoremediation of environmental contaminants.

Contribution of Human Hepatic Cytochrome P450 Isoforms to the Metabolism of Psychotropic Drugs

The metabolic activities of six psychotropic drugs, diazepam, clotiazepam, tofisopam, etizolam, tandospirone, and imipramine, were determined for 14 isoforms of recombinant human hepatic cytochrome P450s (CYPs) and human liver microsomes by measuring the disappearance rate of parent compounds. In vitro kinetic studies revealed that Vmax/Km values in human liver microsomes were the highest for tofisopam, followed by tandospirone>clotiazepam>imipramine, diazepam, and etizolam. Among the recombinant CYPs, CYP3A4 exhibited the highest metabolic activities of all compounds except for clotiazepam and imipramine. The metabolism of clotiazepam was catalyzed by CYP2B6, CYP3A4, CYP2C18, and CYP2C19, and imipramine was metabolized by CYP2D6 most efficiently. In addition, the metabolic activities of diazepam, clotiazepam, and etizolam in human liver microsomes were inhibited by 2.5 microM ketoconazole, a CYP3A4 inhibitor, by 97.5%, 65.1%, and 83.5%, respectively, and the imipramine metabolism was not detected after the addition of 1 or 10 microM quinidine, a CYP2D6 inhibitor. These results suggest that the psychotropic drugs investigated are metabolized predominantly by CYP3A4, except that CYP2D6 catalyzes the metabolism of imipramine. In addition, this approach based on the disappearance rate appears to be useful for the identification of the responsible CYP isoform(s) of older drugs, for which metabolic profiles have not been reported.

Bisphenol A and its methylated congeners inhibit growth and interfere with microtubules in human fibroblasts in vitro

Bisphenol A (BPA), a monomer of polycarbonate plastics and epoxy resins, has previously been reported to induce micronuclei containing whole chromosomes in Chinese hamster V79 cells. In the present study, the aneuploidogenic potential of BPA was investigated in cultured human AG01522C fibroblasts. In contrast to the known aneugens diethylstilbestrol (DES) and 17beta-estradiol, which caused mitotic arrest and the induction of kinetochore-positive micronuclei, BPA did not induce micronuclei and inhibited the proliferation of AG01522C cells in G2 phase and probably also in G1 phase. Fluorescence microscopy of the BPA-treated cells after immunofluorescent staining of microtubules revealed structural abnormalities of the cytoplasmic microtubule complex (CMTC): densely stained rings and loops of tubulin were observed, which increased in number with increasing BPA concentration and were more stable against low temperature than normal microtubules. The mechanisms of the growth inhibition and the interference with microtubules elicited by BPA in AG01522C cells are presently unknown. The formation of rings and loops in the CMTC of AG01522C cells was also observed with two congeners of BPA carrying one and two, respectively, additional methyl groups in ortho-position to the phenolic hydroxyl group at each aromatic ring. However, in contrast to BPA itself, these congeners of BPA behaved "DES-like" by inducing mitotic arrest and kinetochore-positive micronuclei in AG01522C cells.

Establishment of a transgenic cell line stably expressing human cytochrome P450 2C18 and identification of a CYP2C18 clone with exon 5 missing

AIM: The human cytochrome P-450 2C18 (CYP2C18) has been characterized. However, the protein has not been purified from liver and very little is known regarding the specific substrate of CYP2C18. In order to study its enzymatic activity for drug metabolism, the CYP2C18 cDNA was cloned and a stable CHL cell line expressing recombinant CYP 2C18 was established.

METHODS: The human CYP2C18 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR) from total RNAs extracted from human liver and cloned into pGEM-T vector. The cDNA segment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant plasmid of pREP9-CYP2C18 to Chinese hamster lung (CHL) cell. The enzyme activity of CYP2C18 catalyzing oxidation of tolbutamide to hydroxytolbutamide in postmitochondrial supernant (S9) fraction of the cell was determined by high performance liquid chromatography (HPLC).

RESULTS: The amino acid sequence predicted from the cloned cDNA segment was identical to that of reported by Romkes et al^[3] (GenBank accession number: M61856, J05326). The S9 fraction of the established cell line metabolizes tolbutamide to hydroxytolbutamide. Tolbutamide hydroxylase activity was found to be 0.509 ± 0.052 μmol·min^-1·g^-1 S9 protein or 8.82 ± 0.90 mol·min^-1·mol^-1 CYP, but was undetectable in parental CHL cell. In addition, we have identified a CYP2C18 cDNA clone with exon 5 missing.

CONCLUSION: The cDNA of human CYP2C18 was successfully cloned and a cell line, CHL-CYP2C18, efficiently expressing the protein of CYP2C18, was established. A spliced variant of CYP2C18 with exon 5 missing was identified in the cloning process.

Inhibition of human hepatic cytochrome P450s and steroidogenic CYP17 by nonylphenol

Effect of nonylphenol on aminopyrine N-demethylase activity, a typical drug-metabolizing enzyme activity, by ten kinds of human hepatic cytochrome P450s (CYP) and on progesterone 17alpha-hydroxylase activity by steroidogenic CYP17 was investigated. When determined at 2 mM substrate concentration, nonylphenol (1 mM) most efficiently inhibited aminopyrine N-demethylation by CYP2C9 and CYP2C19, by 61% and 59%, respectively, followed by CYP2D6, CYP1A2, CYP2C18 and CYP2C8 (46-51%), whereas inhibition of the activities by other CYPs was less than 27%. Additionally, nonylphenol competitively inhibited diclofenac 4'-hydroxylation by CYP2C9 and S-mephenytoin 4'-hydroxylation by CYP2C19 with Ki values of 5.3 and 37 microM, respectively. Furthermore, nonylphenol exhibited a competitive inhibition of progesterone 17alpha-hydroxylase activity by CYP17 with Ki value of 62 microM. These results suggest that nonylphenol inhibits human hepatic CYPs, especially CYP2C9 and CYP2C19, and steroidogenic CYP17 activities.