Is bisphenol A a weak carcinogen like the natural estrogens and diethylstilbestrol?

Protective Effect of Turmeric against Bisphenol-A Induced Genotoxicity in Rats

In this study, the protective role of turmeric on genotoxic effects of Bisphenol-A exposure in Wistar rats by in vivo experiment were investigated. Bisphenol-A is a known endocrine disruptor and suspected carcinogen, that comes diet through plastics for food packaging and food processing. In this study, rats were divided into three groups of twelve animals each and were administered with Bisphenol-A by oral gavage with levels of 0, 50 and, 100 μg. Half of the animals in each group were fed with feed which contained 3% turmeric (wt/wt), for a period of 4 wk, while the rest of the rats received the same diet treatment without the addition of turmeric. At the end of the experiment, all rats were terminated and the internal organs such as liver, kidney, femurs were collected and analyzed. Mean and SD values were compared by one-way ANOVA and Kruskal-Wallis-Wilcoxon test, the formation of micronuclei was compared using Mann-Whitney U-test. Significant decrease in serum malondialdehyde and urinary 8-hydroxy-2'-deoxyguanosine levels were observed in Bisphenol-A+turmeric groups as compared to Bisphenol-A groups. Bisphenol-A groups exhibited significantly higher mean levels of DNA damage in liver and kidney as compared to the untreated control group. Bisphenol-A group showed significant increase in the formation of micronuclei which was approximately threefold higher as compared to the control group. A significant decrease in DNA migration was observed in Bisphenol-A+turmeric fed groups in liver and kidney. Turmeric feeding significantly inhibited the micronuclei formation induced by Bisphenol-A. The study results indicate that turmeric can protect against Bisphenol-A induced genotoxicity in rats.

Bisphenol A and Phthalates Exhibit Similar Toxicogenomics and Health Effects

Bisphenol A and phthalates are most frequently detected organic pollutants found in our surroundings because of their regular use as plasticizers in daily use polymeric products. BPA is used in manufacturing baby feeding bottles, water pipes, canned food linings, and food packaging materials. Phthalates are used in polyvinyl chloride products including clothing, toys, medical devices, and food packaging. These chemicals are not bound to the matrix and leach out into the surroundings on slight change in the environment, like alteration in pH, temperature, and pressure. Humans are continuously exposed to these chemicals through skin contact, inhalation, or ingestion when the leachates enter food, drinks, air, water, or soil. The Comparative Toxicogenomics Database (CTD) revealed that Bisphenol A has 1932 interactions with genes/proteins and few frequently used phthalates (DEHP, MEHP, DBP, BBP, and MBP) showed 484 gene/protein interactions. Similar toxicogenomics and adverse effects of Bisphenol A and phthalates on human health are attributed to their 89 common interacting genes/proteins.

Biochemical responses of freshwater mussel Unio tumidus to titanium oxide nanoparticles, Bisphenol A, and their combination

Multiple interactions between different pollutants in the surface waters can cause unpredictable consequences. The aim of the study was to evaluate the combined effect of two widespread xenobiotics, titanium oxide nanoparticles (TiO₂) and bisphenol A (BPA), on freshwater bivalve Unio tumidus. The specimens were exposed for 14 days to TiCl₄ (Ti, 1.25 µM), TiO₂ (1.25 μM), BPA (0.88 nM), or their combination (TiO₂ + BPA). Every type of exposure resulted in a particular oxidative stress response: TiO₂ had antioxidant effect, decreasing the generation of reactive oxygen species (ROS) and phenoloxidase (PhO) activity, and doubling reduced glutathione (GSH) concentration in the digestive gland; Ti caused oxidative changes by increasing levels of ROS, PhO and superoxide dismutase; BPA decreased the GSH level by a factor of two. In the co-exposure treatment, these indices as well as lysosomal membrane stability were not affected. All Ti-containing exposures caused elevated levels of metalated metallothionein (Zn,Cu-MT), its ratio to total metallothionein protein, and lactate/pyruvate ratio. Both BPA-containing exposures decreased caspase-3 activity. All exposures, and particularly co-exposure, up-regulated CYP450-dependent oxidation, lipid peroxidation and lipofuscin accumulation, lysosomal cathepsin D and its efflux, as well as alkali-labile phosphates in gonads and caused DNA instability (except for TiO₂). To summarize, co-exposure to TiO₂ + BPA produced an overlap of certain individual responses but strengthened the damage. Development of water purification technologies using TiO₂ requires further studies of the biological effects of its mixtures. U. tumidus can serve as a sentinel organism in such studies.

Cytological Evaluation of the Influence of High and Low Doses of Bisphenol a on an Erythroblastic Cell Line of Porcine Bone Marrow

Introduction

Bisphenol A (BPA) is a substance widely used in industry for the production of polycarbonates and epoxy resins used in packaging and containers for beverages, contact lenses, compact discs (CDs), window panes, and many other elements. This compound belongs to the group of polyphenols and xenoestrogens commonly found in the human environment. What we know about BPA is still insufficient to enable us to protect our health against its adverse effects, and current knowledge of the influence of BPA on erythroblastic cell lines in bone marrow is rather fragmentary. The aim of the experiment was to assess the effect of two doses of BPA (0.05 mg/kg and 0.5 mg/kg b.w. per day) on myeloid haematopoiesis.

Material and Methods

During this experiment, the number of all types of cells in the erythroblastic cell line was evaluated in porcine bone marrow before and after BPA administration.

Results

The obtained results clearly indicate changes in haematopoietic activity of the bone marrow, which was demonstrated by a decrease in erythroblastic cell line production in both experimental groups. The haematological effects of the bone marrow changes were anaemia, caused by a number of erythrocytes which was depressed due to their immaturity, and a significant decrease in mean cellular volume in both groups.

Conclusion

The harmful effect of high and low doses of BPA on haematopoietic processes was proved.

Occurrence, endocrine-related bioeffects and fate of bisphenol A chemical degradation intermediates and impurities: A review

In recent decades, increasing attention has been directed toward the effects of bisphenol A (BPA) as an environmental pollutant, primarily due to its demonstrated endocrine-disruptive effects. A growing body of evidence indicates that many BPA derivatives also exhibit endocrine activity and other adverse biological properties. A review of the published literature was performed to identify BPA degradation intermediates resulting from chemical degradation processes of BPA, as well as BPA's associated co-pollutants. Products of biological metabolism were not included in this study. Seventy-nine chemicals were identified. Of these chemicals, a subset - those containing two 6-membered aromatic rings connected by a central ring-linking carbon - was identified, and a further literature review was conducted to identify demonstrated biological effects associated with the chemicals in this subset. The objectives of this review were to assess the potential risks to human and environmental health associated with BPA derivatives, characterize our current understanding of BPA's degradation intermediates and co-pollutants, and aid in the identification of compounds of interest that have received insufficient scrutiny.

Camptothecin Efficacy to Poison Top1 Is Altered by Bisphenol A in Mouse Embryonic Fibroblasts

Bisphenol A (BPA) is used heavily in the production of polycarbonate plastics, thermal receipt paper, and epoxies. Ubiquitous exposure to BPA has been linked to obesity, diabetes, and breast and reproductive system cancers. Resistance to chemotherapeutic agents has also been shown in cancer cell models. Here, we investigated BPA's ability to confer resistance to camptothecin (CPT) in mouse embryonic fibroblasts (MEFs). MEFs are sensitive to CPT; however, co-exposure of BPA with CPT improved cell survival. Co-exposure significantly reduced Top1-DNA adducts, decreasing chromosomal aberrations and DNA strand break formation. This decrease occurs despite BPA treatment increasing the protein levels of Top1. By examining chromatin structure after BPA exposure, we determined that widespread compaction and loss of nuclear volume occurs. Therefore, BPA reduced CPT activity by reducing the accessibility of DNA to Top1, inhibiting DNA adduct formation, the generation of toxic DNA strand breaks, and improving cell survival.

Bisphenol A Induces Oxidative Stress in Bone Marrow Cells, Lymphocytes, and Reproductive Organs of Holtzman Rats

Bisphenol A (BPA) is an estrogenic chemical used in the production of polycarbonate plastics and epoxy resins. Our earlier studies have demonstrated that BPA is a potent reproductive and genotoxic agent and affects the normal physiological functions. The objective of this study was to evaluate whether exposure to BPA induces oxidative stress. The male Holtzman rats were orally gavaged with BPA (0.01 mg and 5.0 mg/kg/bw) over the period of 6 days. Animals were euthanized by cervical dislocation at the end of the treatments; bone marrow cells and blood lymphocytes were aspirated; testis and epididymis were collected, immediately frozen in liquid nitrogen, and stored at −80°C. These samples were utilized for the determination of lipid peroxidation and various antioxidant enzymes such as superoxide dismutase, catalase, and nonenzymatic reduced glutathione. The results demonstrated that BPA caused an increase in lipid peroxidation and a decrease in activity of various enzymatic and nonenzymatic antioxidants in bone marrow cells, blood lymphocytes, and testicular and epididymal tissues. The findings of the current study suggest that BPA exposure induced oxidative stress, which could be one of the possible mechanisms causing reproductive and genetic toxicity.

Induction of oxidative stress by bisphenol A and its pleiotropic effects

Bisphenol A (BPA) has become a target of intense public scrutiny since concerns about its association with human diseases such as obesity, diabetes, reproductive disorders, and cancer have emerged. BPA is a highly prevalent chemical in consumer products, and human exposure is thought to be ubiquitous. Numerous studies have demonstrated its endocrine disrupting properties and attributed exposure with cytotoxic, genotoxic, and carcinogenic effects; however, the results of these studies are still highly debated and a consensus about BPA's safety and its role in human disease has not been reached. One of the contributing factors is a lack of molecular mechanisms or modes of action that explain the diverse and pleiotropic effects observed after BPA exposure. The increase in BPA research seen over the last ten years has resulted in more studies that examine molecular mechanisms and revealed links between BPA-induced oxidative stress and human disease. Here, a review of the current literature examining BPA exposure and the induction of reactive oxygen species (ROS) or oxidative stress will be provided to examine the landscape of the current BPA literature and provide a framework for understanding how induction of oxidative stress by BPA may contribute to the pleiotropic effects observed after exposure. Environ. Mol. Mutagen. 58:60-71, 2017. © 2017 Wiley Periodicals, Inc.

Interaction of bisphenol A 3,4-quinone metabolite with glutathione and ribonucleosides/deoxyribonucleosides in vitro

Bisphenol A is a monomer used in the manufacture of polycarbonate plastic products, epoxy resin-based food can liners and flame retardants. To determine the genotoxic potential of bisphenol A, the mechanism of the reactions between the reactive electophilic bisphenol A 3,4-quinone (BPAQ) with glutathione and ribonucleosides/deoxyribonucleosides were studied. The obtained results demonstrated that BPAQ reacted with 2'-deoxyguanosine (dG)/guanosine (G), 2'-deoxyadenosine (dA)/adenosine (A), but not with 2'-deoxycytidine (dC)/cytidine (C) and thymidine (T)/uridine (U) in aqueous acetic acid. The reactions were accompanied by loss of deoxyribose, and the rate of depurination by deoxyribonucleoside adducts were faster than that of ribonucleoside adducts. In mixtures of ribonucleosides and deoxyribonucleosides treated with BPAQ, reactions occurred more readily with dG/G than dA/A. The structures of the modified bases were confirmed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). We also found that BPAQ reacted readily with glutathione (GSH) in aqueous acetic acid, and characterized the BPAQ-GSH conjugate by ESI-MS/MS. The in vitro data of depurinating DNA/RNA adducts and BPAQ-GSH adducts may provide appropriate reference for the identification of BPAQ adducts in environmental and biological systems.

Formation and Biological Targets of Quinones: Cytotoxic versus Cytoprotective Effects

Quinones represent a class of toxicological intermediates, which can create a variety of hazardous effects in vivo including, acute cytotoxicity, immunotoxicity, and carcinogenesis. In contrast, quinones can induce cytoprotection through the induction of detoxification enzymes, anti-inflammatory activities, and modification of redox status. The mechanisms by which quinones cause these effects can be quite complex. The various biological targets of quinones depend on their rate and site of formation and their reactivity. Quinones are formed through a variety of mechanisms from simple oxidation of catechols/hydroquinones catalyzed by a variety of oxidative enzymes and metal ions to more complex mechanisms involving initial P450-catalyzed hydroxylation reactions followed by two-electron oxidation. Quinones are Michael acceptors, and modification of cellular processes could occur through alkylation of crucial cellular proteins and/or DNA. Alternatively, quinones are highly redox active molecules which can redox cycle with their semiquinone radical anions leading to the formation of reactive oxygen species (ROS) including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can alter redox balance within cells through the formation of oxidized cellular macromolecules including lipids, proteins, and DNA. This perspective explores the varied biological targets of quinones including GSH, NADPH, protein sulfhydryls [heat shock proteins, P450s, cyclooxygenase-2 (COX-2), glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1, (NQO1), kelch-like ECH-associated protein 1 (Keap1), IκB kinase (IKK), and arylhydrocarbon receptor (AhR)], and DNA. The evidence strongly suggests that the numerous mechanisms of quinone modulations (i.e., alkylation versus oxidative stress) can be correlated with the known pathology/cytoprotection of the parent compound(s) that is best described by an inverse U-shaped dose-response curve.

Possible relationship between endocrine disrupting chemicals and hormone dependent gynecologic cancers

The effects of the natural and synthetic estrogens have been studied for a long time but the data regarding estrogen related chemicals (endocrine disrupting chemicals, EDCs) and their effects on reproductive system are scarce. EDCs are hormone like agents that are readily present in the environment, which may alter the endocrine system of humans and animals. Approximately 800 chemicals are known or suspected to have the potential to function as EDC. Potential role of EDCs on reproductive disease has gained attention in medical literature in recent years. We hypothesize that exposure to low doses of EDCs in a chronic manner could cause hormone dependent genital cancers including ovarian and endometrial cancer. Long term exposure to low concentrations of EDCs may exert potentiation effect with each other and even with endogenous estrogens and could inhibit enzymes responsible for estrogen metabolism. Exposure time to these EDCs is essential as we have seen from Diethylstilbestrol experience. Dose-response curves of EDCs are also unpredictable. Hence mode of action of EDCs are more complex than previously thought. In the light of these controversies lower doses of EDCs in long term exposure is not harmless. Possibility of this relationship and this hypothesis merit further investigation especially through in vivo studies that could better show the realistic environmental exposure. With the confirmation of our hypothesis, possible EDCs could be identified and eliminated from general use as a public health measure.

Effects of Low-Dose Bisphenol A on DNA Damage and Proliferation of Breast Cells: The Role of c-Myc

BACKGROUND

Humans are exposed to low-dose bisphenol A (BPA) through plastic consumer products and dental sealants containing BPA. Although a number of studies have investigated the mammary gland effects after high-dose BPA exposure, the study findings differ. Furthermore, there has been a lack of mechanistic studies.

OBJECTIVE

The objective of this study was to investigate the effect and the mechanism of low-dose BPA in mammary gland cells.

METHODS

We evaluated DNA damage following BPA exposure using the comet assay and immunofluorescence staining, and used cell counting and three-dimensional cultures to evaluate effects on proliferation. We examined the expressions of markers of DNA damage and cell-cycle regulators by immunoblotting and performed siRNA-mediated gene silencing to determine the role of c-Myc in regulating BPA's effects.

RESULTS

Low-dose BPA significantly promoted DNA damage, up-regulated c-Myc and other cell-cycle regulatory proteins, and induced proliferation in parallel in estrogen receptor-α (ERα)-negative mammary cells. Silencing c-Myc diminished these BPA-induced cellular events, suggesting that c-Myc is essential for regulating effects of BPA on DNA damage and proliferation in mammary cells.

CONCLUSIONS

Low-dose BPA exerted c-Myc-dependent genotoxic and mitogenic effects on ERα-negative mammary cells. These findings provide significant evidence of adverse effects of low-dose BPA on mammary cells.

Bisphenol A as epigenetic modulator: setting the stage for carcinogenesis?

BACKGROUND

Bisphenol A (BPA) is one of the most widely produced chemicals worldwide and is often used in the production of food and beverage containers. As a result of BPA contact with food, drink and toiletries, its ingestion and absorption by humans has been growing. The industrialization and modern lifestyles brought a constant exposure to several health-disturbing compounds and ushered a new era of chronic diseases. The endocrine disruptor potential of BPA is well known, but the research around its epigenotoxic effects raised further concerns whether chronic exposure to BPA can contribute to chronic human illness, including cancer in hormone-sensitive organs.

MATERIALS AND METHODS

Focusing on computerized databases, we reviewed original and review articles which elucidate and link some of the information already available about BPA and related epigenetic alterations.

RESULTS

A number of studies indicate that short-term administration of low or high-doses of BPA may be associated with an increased risk of epigenetic modifications, increasing the risk for carcinogenesis. However, it is clear that more studies considering real daily exposures are essential to define a real tolerable daily intake and to tighten up manufactory regulations.

CONCLUSION

In this review, we highlight some evidences suggesting a relationship between BPA exposure, genotoxic activity and epigenetic modifications, which may prime for carcinogenesis.

Association between urinary levels of bisphenol-A and estrogen metabolism in Korean adults

Bisphenol-A (BPA) possesses estrogenic properties both in vitro and in vivo as an endocrine disrupting chemical. Humans experience a long-term and cumulative exposure to BPA. BPA was detectable in 97.3% of 1904 urine specimens from Korean adults. We investigated urinary estrogen concentrations in subjects with low and high BPA concentrations and its possible association with estrogen metabolism. Urine samples were collected from a high BPA concentration group (BPA-H; n=100, 11.05 ± 20.47 μg/g creatinine) and a low BPA concentration group (BPA-L; n=100, 0.70 ± 0.22 μg/g creatinine) from Korea Biomonitoring Program of Hazardous Materials Survey 2009-2010. Urinary estrogens were enzymatically hydrolyzed, extracted, and then derivatized for quantitative analysis by gas chromatography-mass spectrometry. Estrogen levels were higher in the BPA-H group than in the BPA-L group. Concentrations of estrone, 17β-estradiol, and their hydroxylated metabolites in both men and women were significantly higher in the BPA-H group than in the BPA-L group (p<0.04). Furthermore, in the BPA-H group, estrogen metabolism to 4-hydroxy-estrone and 4-hydroxy-17β-estradiol was more active than that to 2-hydroxy-estrone and 2-hydroxy-17β-estradiol. Although single measurement and/or single spot urine samples limit the measurement of long-term exposure to BPA, we found significant differences of estrogen metabolism in the BPA-H and the BPA-L groups. The increase of hydroxyestrogens, especially 4-hydroxyestrogens, can be an important factor resulting negative effects of prolonged exposure to BPA.

Expression and DNA methylation changes in human breast epithelial cells after bisphenol A exposure

It has been suggested that xenoestrogens, a group of agents termed endocrine disruptors, may contribute to the development of hormone-dependent cancers, such as breast and endometrial cancers. We previously demonstrated that the xenoestrogen, bisphenol A (BPA), was able to induce the transformation in vitro of human breast epithelial cells. The normal-like human breast epithelial cell line, MCF-10F, formed tubules in collagen (3-D cultures), although after treatment with BPA (10-5 M and 10-6 M BPA) the cells produced less tubules (73% and 80%, respectively) and some spherical masses (27% and 20%, respectively). In the present study, expression and DNA methylation analyses were performed in these cells after exposure to BPA. These cells showed an increased expression of BRCA1, BRCA2, BARD1, CtIP, RAD51 and BRCC3, all of which are genes involved in DNA repair, as well as the downregulation of PDCD5 and BCL2L11 (BIM), both of which are involved in apoptosis. Furthermore, DNA methylation analysis showed that the BPA exposure induced the hypermethylation of BCL2L11, PARD6G, FOXP1 and SFRS11, as well as the hypomethylation of NUP98 and CtIP (RBBP8). Our results indicate that normal human breast epithelial cells exposed to BPA have increased expressions of genes involved in DNA repair in order to overcome the DNA damage induced by this chemical. These results suggest that the breast tissue of women with BRCA1 or BRCA2 mutations could be more susceptible to the effects of BPA.

The naphthol selective estrogen receptor modulator (SERM), LY2066948, is oxidized to an o-quinone analogous to the naphthol equine estrogen, equilenin

o-Quinone forming estrogens and selective estrogen receptor modulators (SERMs) have been associated with carcinogenesis. LY2066948, a novel SERM in development by Eli Lilly for the treatment of uterine fibroids and myomas, has structural similarity to the equine estrogen equilenin present in hormone replacement formulations; both contain a naphthol group susceptible to oxidative metabolism to o-quinones. LY2066948 was synthesized and assayed for antiestrogenic activity, and in cell culture was confirmed to be a more potent antiestrogen than the prototypical SERM, 4-hydroxytamoxifen. Oxidation of LY2066948 with 2-iodoxybenzoic acid gave an o-quinone (t(1/2)=3.9 ± 0.1h) which like 4-hydroxyequilenin-o-quinone (t(1/2)=2.5 ± 0.2 h) was observed to be exceptionally long-lived with the potential to cause cytotoxicity and/or genotoxicity. In model reactions with tyrosinase, the catechol metabolites of LY2066948 and equilenin were products; interestingly, in the presence of ascorbate to inhibit autoxidation, these catechols were formed quantitatively. Tyrosinase incubations in the presence of GSH gave the expected GSH conjugates resulting from trapping of the o-quinones, which were characterized by LC-MS/MS. Incubations of LY2066948 or equilenin with rat liver microsomes also gave detectable o-quinone trapped GSH conjugates; however, as observed with other SERMs, oxidative metabolism of LY2066948 mainly occurred on the amino side chain to yield the N-dealkylated metabolite. CYP1B1 is believed to be responsible for extra-hepatic generation of genotoxic estrogen quinones and o-quinone GSH conjugates were detected in equilenin incubations. However, in corresponding incubations with CYP1B1 supersomes, no o-quinone GSH conjugates of LY2066948 were detected. These studies suggest that although the naphthol group is susceptible to oxidative metabolism to long-lived o-quinones, the formation of these quinones by cytochrome P450 can be attenuated by the chemistry of the remainder of the molecule as in the case of LY2066948.

The etiology and prevention of breast cancer

Metabolism of estrogens via the catechol estrogen pathway is characterized by a balanced set of activating and protective enzymes (homeostasis). Disruption of homeostasis, with excessive production of catechol estrogen quinones, can lead to reaction of these quinones with DNA to form depurinating estrogen-DNA adducts. Some of the mutations generated by these events can lead to initiation of breast cancer. A wealth of evidence, from studies of metabolism, mutagenicity, cell transformation and carcinogenicity, demonstrates that estrogens are genotoxic. Women at high risk for breast cancer, or diagnosed with the disease, have relatively high levels of depurinating estrogen-DNA adducts compared to normal-risk women. The dietary supplements N-acetylcysteine and resveratrol can inhibit formation of catechol estrogen quinones and their reaction with DNA to form estrogen-DNA adducts, thereby preventing initiation of breast cancer.

Bisphenol A and phthalates exhibit similar toxicogenomics and health effects

Plastics are widely used in modern life, and their unbound chemicals bisphenol A and phthalates can leach out into the surrounding environment. BPA and PAEs have recently attracted the special attention of the scientific community, regulatory agencies and the general public because of their high production volume, widespread use of plastics, and endocrine-disrupting effects. In The Comparative Toxicogenomics Database, BPA and five most frequently curated PAEs (DEHP/MEHP and DBP/BBP/MBP) were found to have 1932 and 484 interactions with genes/proteins, respectively. Five of their top ten toxicity networks were found to be involved in inflammation, and their top ten diseases included genital, prostatic, endomentrial, ovarian and breast diseases. BPA and PAEs were found to exhibit similar toxicogenomics and adverse effects on human health owning to their 89 common interacting genes/proteins. These 89 genes/proteins may serve as biomarkers to assay the toxicities of different chemicals leached out from the widely used plastics.