UVB-Exposed Chlorinated Bisphenol A Generates Phosphorylated Histone H2AX in Human Skin Cells

High cytotoxicity of a degraded TBBPA, dibromobisphenol A, through apoptotic and necrosis pathways

Halogenated flame retardants comprising bisphenol A (BPA) derivatives, such as tetrabromobisphenol A (TBBPA), have been studied their adverse effects on human health. However, despite the fact that these halogenated BPAs are easily degraded in the environment, the risks to living organisms due to these degraded products have mostly been overlooked. To evaluate the potential toxicity of degraded TBBPAs and related compounds, we examined the cytotoxicity of halogenated bisphenol A derivatives possessing one to four halogen atoms in vitro. The results indicated that the degraded TBBPA derivatives exhibited strong cytotoxicity against HeLa cells than TBBPA. Interestingly, the di-halogenated BPA derivatives possessing two halogen atoms exhibited the strongest cytotoxicity among tested compounds. In addition, a lactate dehydrogenase release assay, fluorescence spectroscopy and flow cytometry results indicated that dibromo-BPA and diiodo-BPA induced both apoptotic and necrotic cell death by damaging the cell membranes of HeLa cells. Moreover, Escherichia coli growth was inhibited in the presence of dehalogenated TBBPA and related compounds. These findings suggest that halogenated BPA derivatives that leak from various flame-retardant-containing products require strict monitoring, as not only TBBPA but also its degraded products in environment can exert adverse effects to human health.

Adverse (geno)toxic effects of bisphenol A and its analogues in hepatic 3D cell model

Bisphenol A (BPA) is one of the most widely used and versatile chemical compounds in polymer additives and epoxy resins for manufacturing a range of products for human applications. It is known as endocrine disruptor, however, there is growing evidence that it is genotoxic. Because of its adverse effects, the European Union has restricted its use to protect human health and the environment. As a result, the industry has begun developing BPA analogues, but there are not yet sufficient toxicity data to claim that they are safe. We investigated the adverse toxic effects of BPA and its analogues (BPS, BPAP, BPAF, BPFL, and BPC) with emphasis on their cytotoxic and genotoxic activities after short (24-h) and prolonged (96-h) exposure in in vitro hepatic three-dimensional cell model developed from HepG2 cells. The results showed that BPFL and BPC (formed by an additional ring system) were the most cytotoxic analogues that affected cell viability, spheroid surface area and morphology, cell proliferation, and apoptotic cell death. BPA, BPAP, and BPAF induced DNA double-strand break formation (γH2AX assay), whereas BPAF and BPC increased the percentage of p-H3-positive cells, indicating their aneugenic activity. All BPs induced DNA single-strand break formation (comet assay), with BPAP (≥0.1 μM) being the most effective and BPA and BPC the least effective (≥1 μM) under conditions applied. The results indicate that not all of the analogues studied are safer alternatives to BPA and thus more in-depth research is urgently needed to adequately evaluate the risks of BPA analogues and assess their safety for humans.

Genotoxic potential of bisphenol A: A review

Bisphenol A (BPA), as a major component of some plastic products, is abundant environmental pollutant. Due to its ability to bind to several types of estrogen receptors, it can trigger multiple cellular responses, which can contribute to various manifestations at the organism level. The most studied effect of BPA is endocrine disruption, but recently its prooxidative potential has been confirmed. BPA ability to induce oxidative stress through increased ROS production, altered activity of antioxidant enzymes, or accumulation of oxidation products of biomacromolecules is observed in a wide range of organisms - estrogen receptor-positive and -negative. Subsequently, increased intracellular oxidation can lead to DNA damage induction, represented by oxidative damage, single- and double-strand DNA breaks. Importantly, BPA shows several mechanisms of action and can trigger adverse effects on all organisms inhabiting a wide variety of ecosystem types. Therefore, the main aim of this review is to summarize the genotoxic effects of BPA on organisms across all taxa.

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.

Biomonitoring of human exposures to chlorinated derivatives and structural analogs of bisphenol A

The high reactivity of bisphenol A (BPA) with disinfectant chlorine is evident in the instantaneous formation of chlorinated BPA derivatives (ClxBPA) in various environmental media that show increased estrogen-activity when compared with that of BPA. The documented health risks associated with BPA exposures have led to the gradual market entry of BPA structural analogs, such as bisphenol S (BPS), bisphenol F (BPF), bisphenol B (BPB), etc. A suite of exposure sources to ClxBPA and BPA analogs in the domestic environment is anticipated to drive the nature and range of halogenated BPA derivatives that can form when residual BPA comes in contact with disinfectant in tap water and/or consumer products. The primary objective of this review was to survey all available studies reporting biomonitoring protocols of ClxBPA and structural BPA analogs (BPS, BPF, BPB, etc.) in human matrices. Focus was paid on describing the analytical methodologies practiced for the analysis of ClxBPA and BPA analogs using hyphenated chromatography and mass spectrometry techniques, because current methodologies for human matrices are complex. During the last decade, an increasing number of ecotoxicological, cell-culture and animal-based and human studies dealing with ClxBPA exposure sources and routes of exposure, metabolism and toxicity have been published. Up to date findings indicated the association of ClxBPA with metabolic conditions, such as obesity, lipid accumulation, and type 2 diabetes mellitus, particularly in in-vitro and in-vivo studies. We critically discuss the limitations, research needs and future opportunities linked with the inclusion of ClxBPA and BPA analogs into exposure assessment protocols of relevant epidemiological studies.

γ-H2AX induced by linear alkylbenzene sulfonates is due to deoxyribonuclease-1 translocation to the nucleus via actin disruption

Phosphorylation of histone H2AX (γ-H2AX) occurs following formation of DNA double strand breaks (DSBs). Other types of DNA damage also generate DSBs through DNA replication and repair, leading to the production of γ-H2AX. In the present study, we demonstrated that linear alkylbenzene sulfonates (LAS), the most widely used and non-genotoxic anionic surfactants, could generate γ-H2AX via a novel pathway. Breast adenocarcinoma MCF-7 cells were treated with five kinds of LAS with alkyl chains ranging from 10 to 14 carbon units (C10-C14LAS). The generation of DSBs and subsequent production of γ-H2AX increased in a manner that depended on the number of carbon units in LAS. γ-H2AX could also be generated with non-cytotoxic doses of LAS and was independent of the cell cycle, indicating the non-apoptotic and DNA replication-independent formation of DSBs. The generation of γ-H2AX could be attenuated by EGTA and ZnCl2, deoxyribonuclease-1 (DNase I) inhibitors, as well as by the knockdown of DNase I. LAS weakened the interaction between DNase I and actin, and the enhanced release of DNase I was dependent on the number of carbon units in LAS. DNase I released by the LAS treatment translocated to the nucleus, in which DNase I attacked DNA and generated γ-H2AX. These results suggested that the LAS-induced generation of γ-H2AX could be attributed to the translocation of DNase I to the nucleus through the disruption of actin, and not to LAS-induced DNA damage.

Evaluation of chemical phototoxicity, focusing on phosphorylated histone H2AX

Histone H2AX is a minor component of nuclear histone H2A. The phosphorylation of histone H2AX at Ser 139, termed γ-H2AX, was originally identified as an early event after the direct formation of DNA double-strand breaks (DSBs) by ionizing radiation. Now, the generation of γ-H2AX is also considered to occur in association with secondarily formed DSBs by cellular processing such as DNA replication and repair at the site of the initial damage, including DNA adducts, crosslinks, and UV-induced photolesions. Therefore, γ-H2AX is currently attracting attention as a new biomarker for detecting various genotoxic insults. We have determined the toxic impact of various environmental stresses such as chemicals, light and/or their coexposure using γ-H2AX, and found that the γ-H2AX assay exhibited high sensitivity and a low false-positive rate as a detection system of genotoxic potential. In this review, we introduced our recent findings concerning the evaluation of chemical phototoxicity, focusing on γ-H2AX.

Influence of household cleaning practices on the magnitude and variability of urinary monochlorinated bisphenol A

Low-dose health effects of BPA have not been adequately explored in the presence of BPA metabolites of chlorinated structure that may exert larger estrogenic effects than those of their parent compound. We hypothesized that chlorine-containing cleaning products used in household cleaning activities could modify the magnitude of total urinary BPA concentration measurements via the production of chlorinated BPA (ClBPA) derivatives. Our objective was to investigate the influence of typical household cleaning activities (dishwashing, toilet cleaning, mopping, laundry, etc.) on the magnitude and variability of urinary total BPA and mono-ClBPA levels in the general adult population. A cross-sectional study (n=224) included an adult (≥18 years) pool of participants from the general population of Nicosia, Cyprus. First morning urine voids were collected, and administered questionnaires included items about household cleaning habits, demographics, drinking water consumption rates and water source/usage patterns. Urinary concentrations of total BPA (range: 0.2-82 μg L(-1)), mono-ClBPA (16-340 ng L(-1)), and total trihalomethanes (0.1-5.0 μg L(-1)) were measured using gas chromatography coupled with triple quadrupole mass spectrometry and large volume injection. Linear multiple regression analysis revealed that dishwashing along with age and gender (females) were able to predict urinary mono-ClBPA levels (ng g(-1)), even after adjusting for covariates; this was not the case for urinary total BPA levels (ng g(-1)). Significant (p<0.001) association was observed between urinary mono-ClBPA and THM levels, underlying the important role of disinfectant (chlorine) in promoting formation of both ClBPA and THM. Urinary mono-ClBPA levels were measured for the first time using an appreciable sample size, highlighting the co-occurring patterns of both total BPA and mono-ClBPA. Epidemiological studies and probabilistic BPA risk assessment exercises should consider assessing daily intake estimates for chlorinated BPA compounds, as well.

Silver ions enhance UVB-induced phosphorylation of histone H2AX

Silver (Ag) is used in a wide range of industries including healthcare, food, cosmetics, and environmental industries due to its antibacterial properties. The rapidly expanding use of Ag has raised issues concerning its toxicity in humans. However, studies investigating the effects of Ag on humans are very limited, and the combined effects of Ag and other environmental factors have not yet been determined. Ultraviolet (UV) radiation in sunlight is the most prominent and ubiquitous physical stressor in our natural environment. In this study, we investigated the genotoxic potential of combined exposure to Ag(+) (AgNO3) and UVB in the human keratinocyte cell line, HaCaT, by measuring the generation of phosphorylated histone H2AX, which is currently attracting attention as a biomarker for the detection of genotoxic insults. We found that the generation of γ-H2AX was synergistically enhanced when cells were coexposed to Ag(+) and UVB. Furthermore, we showed that the enhanced generation of γ-H2AX could be attributed to the increased formation of UVB-induced cyclobutane pyrimidine dimers and (6-4) photoproducts. These lesions, if not repaired properly, are the major causal factor for skin carcinogenesis. Our results provide an important insight into influence of Ag on the genotoxic potency of sunlight.

Long-term effects of chromatin remodeling and DNA damage in stem cells induced by environmental and dietary agents

The presence of histones acts as a barrier to protein access; thus chromatin remodeling must occur for essential processes such as transcription and replication. In conjunction with histone modifications, DNA methylation plays critical roles in gene silencing through chromatin remodeling. Chromatin remodeling is also interconnected with the DNA damage response, maintenance of stem cell properties, and cell differentiation programs. Chromatin modifications have increasingly been shown to produce long-lasting alterations in chromatin structure and transcription. Recent studies have shown environmental exposures in utero have the potential to alter normal developmental signaling networks, physiologic responses, and disease susceptibility later in life during a process known as developmental reprogramming. In this review we discuss the long-term impact of exposure to environmental compounds, the chromatin modifications that they induce, and the differentiation and developmental programs of multiple stem and progenitor cell types altered by exposure. The main focus is to highlight agents present in the human lifestyle that have the potential to promote epigenetic changes that impact developmental programs of specific cell types, may promote tumorigenesis through altering epigenetic marks, and may be transgenerational, for example, those able to be transmitted through multiple cell divisions.

Phosphorylation of histone H2AX generated by linear alkylbenzene sulfonates and its suppression by UVB exposure

We previously demonstrated that the nonionic surfactants, nonylphenol polyethoxylates (NPEOs) induced the phosphorylation of histone H2AX (γ-H2AX), accompanied by DNA double-strand breaks (DSBs), and that exposure to ultraviolet (UV) degraded NPEOs, which sometimes enhanced their DNA-damaging ability. In this study, we showed that linear alkylbenzene sulfonates (LAS), general anion surfactants, also generated DSBs with γ-H2AX, and this ability was attenuated by UVB exposure. In the human breast adenocarcinoma cell line, MCF-7, γ-H2AX was generated in a dose-dependent manner immediately after cells were treated with LAS, and this was attributed to the formation of DSBs and was independent of cell cycle phases. The ability to generate γ-H2AX was markedly reduced in LAS exposed to UVB. HPLC analysis revealed that LAS were a mixture of various alkyl chain lengths, the peaks of which were detected at individual retention times. UVB evenly decreased all peaks of LAS, without migration of peaks to other retention times, which indicated that UVB may degrade the benzene ring of LAS, but did not shorten the alkyl chains. UVB is an important environmental factor in the degradation of LAS exhibiting the ability to induce DSBs, the most serious type of DNA damage.

Flow cytometric evaluation of nanoparticles using side-scattered light and reactive oxygen species-mediated fluorescence-correlation with genotoxicity

We recently clarified that the side-scatter(ed) light (SSC) of flow cytometry (FCM) could be used as a guide to measure the uptake potential of nanoparticles [ Suzuki et al. Environ. Sci. Technol. 2007 , 41 , 3018 - 3024 ]. In this paper, the method was improved so as to be able to determine simultaneously the uptake potential of nanoparticles and the production of reactive oxygen species (ROS), and correlations with genotoxicity were evaluated. In the FCM analysis, SSC and fluorescence of 6-carboxy-2,7'-diclorodihydrofluorescein diacetate, di(acetoxy ester) based on ROS production were concurrently detected after treatments with ZnO, CuO, Fe(3)O(4), TiO(2), and Ag nanoparticles. The ZnO and CuO nanoparticles caused high ROS production, which was more significant in the cells with higher SSC intensity. The increase of SSC intensity was more significant for TiO(2) than ZnO and CuO, whereas ROS production was higher for ZnO and CuO than TiO(2), suggesting that the extent of ROS production based on the uptake of nanoparticles differed with each kind of nanoparticle. ROS production was correlated with generation of the phosphorylated histone H2AX (γ-H2AX), a marker of DNA damage, and an antioxidant, n-acetylcysteine, could partially suppress the γ-H2AX. This method makes it possible to predict not only uptake potential but also genotoxicity.

Cytotoxic and genotoxic effects of multi-wall carbon nanotubes on human umbilical vein endothelial cells in vitro

Carbon nanomaterials have multiple applications in various areas. However, it has been suggested that exposure to nanoparticles may be a risk for the development of vascular diseases due to injury and dysfunction of the vascular endothelium. Therefore, in the present study, the cytotoxic and genotoxic effects of multi-wall carbon nanotubes (MWCNTs) on human umbilical vein endothelial cells (HUVECs) were evaluated. Optical and transmission electronic microscopy (TEM) study showed that MWCNTs were able to enter cells rapidly, distribute in the cytoplasm and intracellular vesicles and induce morphological changes. Exposure to MWCNTs reduced the viability of HUVECs, and induced apoptosis in HUVECs. Furthermore, MWCNTs could cause DNA damage as indicated by the formation of γH2AX foci. MWCNTs also affected cellular redox status, e.g., increasing intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels, as well as altering superoxide dismutase (SOD) activity and glutathione peroxidase (GSH-Px) levels. On the other hand, the free radical scavenger N-acetyl-l-cysteine (NAC) preincubation can inhibit the cytotoxic and genotoxic effects of MWCNTs. Taken together, these results demonstrated that MWCNTs could induce cytotoxic and genotoxic effects in HUVECs, probably through oxidative damage pathways.