Elucidation of the Effects of Bisphenol A and Structural Analogs on Germ and Steroidogenic Cells Using Single Cell High-Content Imaging

Mitigating bisphenol A-induced apoptosis in KGN cells: the therapeutic role of 1,25-dihydroxyvitamin D3 through upregulation of PGC-1α expression and inhibition of the mitochondrial cytochrome c pathway

PURPOSE

This study investigated the potential of 1,25-dihydroxyvitamin D3 (1,25(OH)2VD3) to mitigate bisphenol A (BPA)-induced apoptosis in human ovarian granulosa KGN cells with the aim of establishing a theoretical foundation for understanding of how vitamin D improved ovarian function in patients with polycystic ovary syndrome (PCOS).

METHODS

The impact of varying concentrations of BPA and 1,25(OH)2VD3 on KGN cell viability was elucidated. It was established that BPA-induced apoptosis in KGN cells. Subsequently, KGN cells underwent pretreatment with 1,25(OH)2VD3, followed by exposure to BPA. The apoptosis rate, reactive oxygen species (ROS) levels, and mitochondrial function of the cells were meticulously assessed, along with the expression levels of genes associated with apoptosis as well as antioxidant and mitochondrial biogenesis.

RESULTS

BPA induced a notable increase in apoptosis (P < 0.001) and oxidative stress (P < 0.001) in KGN cells, accompanied by a significant reduction in mitochondrial membrane potential (P < 0.001) and severe impairment of mitochondrial function. Following pretreatment of KGN cells with 1,25(OH)2VD3, there was a significant decrease in the apoptosis rate (P = 0.004), coupled with a reduction in ROS production (P = 0.002). Concomitantly, the upregulation of PGC-1α (P = 0.009) and SOD (P = 0.018) was observed, while mRNA expression of BAX (P = 0.011), Cyt c (P = 0.001), Apaf-1 (P = 0.012), caspase-9 (P < 0.001), and caspase-3 (P = 0.011) was downregulated. Notably, the mitigation of mitochondrial damage was evident through restored mitochondrial membrane potential (P < 0.001), as corroborated by electron microscope results.

CONCLUSIONS

1,25(OH)2VD3 mitigated BPA-induced damage and apoptosis in KGN cells by upregulating the expression of PGC-1α and impeding the mitochondrial cytochrome c (Cyt c) apoptotic pathway. This study established a novel theoretical foundation for utilizing vitamin D in the treatment of PCOS patients.

High-throughput transcriptomics toxicity assessment of eleven data-poor bisphenol A alternatives

Bisphenol A (BPA), a widely used chemical in the production of plastics and epoxy resins, has garnered significant attention due to its association with adverse health effects, particularly its endocrine-disrupting properties. Regulatory measures aimed at reducing human exposure to BPA have led to a proliferation of alternative chemicals used in various consumer and industrial products. While these alternatives serve to reduce BPA exposure, concerns have arisen regarding their safety and potential toxicity as regrettable substitutes. Previous efforts have demonstrated that in vitro high-throughput transcriptomics (HTTr) studies can be used to assess the endocrine-disrupting potential of BPA alternatives, and this strategy produces transcriptomic points-of-departure (tPODs) that are protective of human health when compared to the PODs from traditional rodent studies. In this study, we used in vitro HTTr to assess the potential for toxicity of eleven data-poor legacy chemicals sharing structural similarities to BPA. Human breast cancer MCF-7 cells were exposed to BPA and 11 alternatives at concentrations ranging from 0.1 to 25 μM to assess toxicity. Analysis of global transcriptomic changes and a previously characterized estrogen receptor alpha (ERα) transcriptomic biomarker signature revealed that 9 of 11 chemicals altered gene expression relative to controls. One of the chemicals (2,4'-Bisphenol A) activated the ERα biomarker at the same concentration as BPA (i.e., 4,4'-BPA) but was deemed to be more potent as it induced global transcriptomic changes at lower concentrations. These results address data gaps in support of ongoing screening assessments to identify BPA alternatives with hazard potential and help to identify potential candidates that may serve as safer alternatives.

Developmental effects and lipid disturbances of zebrafish embryos exposed to three newly recognized bisphenol A analogues

Bisphenol G (BPG), bisphenol M (BPM) and bisphenol TMC (BPTMC), are newly recognized analogues of bisphenol A (BPA), which have been detected in multiple environmental media. However, the understanding of their negative impacts on environmental health is limited. In this study, zebrafish embryos were exposed to BPA and the three analogues (0.1, 10, and 1000 μg/L) to identify their developmental toxic effects. According to our results, all of the three analogues induced significant developmental disorders on zebrafish embryos including inhibited yolk sac absorption, altered heart rate, and teratogenic effects. Oil Red O staining indicated lipid accumulation in the yolk sac region of zebrafish after bisphenol analogues exposure, which was consistent with the delayed yolk uptake. Untargeted lipidomic analysis indicated the abundance of triacylglycerols, ceramides and fatty acids was significantly altered by the three analogues. The combined analysis of lipidomics and transcriptomics results indicated BPG and BPM affected lipid metabolism by disrupting peroxisome proliferator-activated receptor pathway and interfering with lipid homeostasis and transport. This partly explained the morphological changes of embryos after bisphenol exposure. In conclusion, our study reveals that BPG, BPM and BPTMC possess acute and developmental toxicity toward zebrafish, and the developmental abnormalities are associated with the disturbances in lipid metabolism.

Interpretation of in vitro concentration-response data for risk assessment and regulatory decision-making: Report from the 2022 IWGT quantitative analysis expert working group meeting

Quantitative risk assessments of chemicals are routinely performed using in vivo data from rodents; however, there is growing recognition that non-animal approaches can be human-relevant alternatives. There is an urgent need to build confidence in non-animal alternatives given the international support to reduce the use of animals in toxicity testing where possible. In order for scientists and risk assessors to prepare for this paradigm shift in toxicity assessment, standardization and consensus on in vitro testing strategies and data interpretation will need to be established. To address this issue, an Expert Working Group (EWG) of the 8th International Workshop on Genotoxicity Testing (IWGT) evaluated the utility of quantitative in vitro genotoxicity concentration-response data for risk assessment. The EWG first evaluated available in vitro methodologies and then examined the variability and maximal response of in vitro tests to estimate biologically relevant values for the critical effect sizes considered adverse or unacceptable. Next, the EWG reviewed the approaches and computational models employed to provide human-relevant dose context to in vitro data. Lastly, the EWG evaluated risk assessment applications for which in vitro data are ready for use and applications where further work is required. The EWG concluded that in vitro genotoxicity concentration-response data can be interpreted in a risk assessment context. However, prior to routine use in regulatory settings, further research will be required to address the remaining uncertainties and limitations.

Reproductive toxicity of emerging plasticizers, flame retardants, and bisphenols, using culture of the rat fetal testis†

The use of bis (2-ethylhexyl) phthalate (DEHP), 2,2'4,4'-tetrabromodiphenyl ether (BDE47), and bisphenol A (BPA), as plasticizers, flame retardants, and epoxy resins, respectively, has been regulated due to their endocrine disrupting activities. Replacements for these chemicals are found in human matrices, yet the endocrine disrupting potential of these emerging contaminants is poorly characterized. We compared the effects of legacy chemicals with those of their replacements using fetal rat testis organ culture. Fetal testes sampled at gestation day 15 were grown ex vivo, and the impact was evaluated after a 3-day exposure to 10 μM of each legacy chemical; two BPA analogs (bisphenol M and bisphenol TMC); three replacements for DEHP/MEHP (2,2,4-trimethyl-1,3-pentanediol diisobutyrate, diisononyl-phthalate, and diisodecyl adipate); or two replacements for BDE47 (tributoxyethyl phosphate and isopropylated triphenyl phosphate). We showed that only BPA and MEHP significantly decrease testosterone secretions after 24 h, while BPM and BPTMC have the opposite effect. Luteinizing hormone-stimulated testosterone was reduced by BPA and MEHP but was increased by BPTMC. After exposure, testes were used for immunofluorescent staining of germ cells, Sertoli cells, and Leydig cells. Interestingly, exposures to BPM or BPTMC induced a significant increase in the Leydig cell density and surface area. A decrease in germ cell density was observed only after treatment with MEHP or BDE47. MEHP also significantly decreased Sertoli cell proliferation. These studies show that some replacement chemicals can affect testicular function, while others appear to show little toxicity in this model. These findings provide essential information regarding the need for their regulation.

Toxicity of bisphenol A and its replacements in the mice Leydig cells in vitro

The aim of the study was to examine the potential impacts of bisphenol A (BPA) and its analogues BPB, BPF, and BPS on mice TM3 Leydig cells, with respect to basal cell viability parameters such as metabolic activity, cell membrane integrity, and lysosomal activity after 48-h exposure. In addition, monitoring of potential bisphenol´s actions included evaluation of ROS production and gap junctional intercellular communication (GJIC) complemented by determination of testosterone secretion. Obtained results revealed significant inhibition in mitochondrial activity started at 10 microg/ml of bisphenols after 48-h exposure. Cell membrane integrity was significantly decreased at 5 microg/ml of BPA and BPF and 10, 25, and 50 microg/ml of BPA and BPS. The lysosomal activity was significantly affected at 10, 25, and 50 microg/ml of applied bisphenols. A significant overproduction of ROS was recorded mainly at 5 and 10 microg/ml of tested compounds. In addition, significant inhibition of GJIC was observed at 5 microg/ml of BPB followed by a progressive decline at higher applied doses. In the case of testosterone production, a significant decline was confirmed at 10, 25 and 50 microg/ml.

In silico profiling of endocrine-disrupting potential of bisphenol analogues and their halogenated transformation products

Due to its endocrine-disrupting properties, bisphenol A (BPA) is being phased out from plastics, thermal paper and epoxy resins, and its replacements are being introduced into the market. Bisphenols are released into the environment, where they can undergo halogenation. Unlike BPA, the endocrine-disrupting potential of BPA analogues and their halogenated transformation products has not been extensively studied. The aim of this study was to evaluate the endocrine-disrupting potential of 18 BPA analogues and their halogenated derivatives by calculating affinities for 14 human nuclear receptors utilizing the Endocrine Disruptome and VirtualToxLab™ in silico tools. Our simulations identified AR, ERs, and GR as the most favorable targets of bisphenols and their derivatives. Several BPA analogues displayed a higher predicted potential for endocrine disruption than BPA. Our models highlighted BPZ and BPPH as the most hazardous in terms of predicted endocrine activities. Halogenation, in general, was predicted to increase the binding affinity of bisphenols for AR, ERβ, MR, GR, PPARγ, and TRβ. Notably, mono- or 2,2'-di-halogenated bisphenols exhibited the highest potential for endocrine disruption. In vitro corroboration of the obtained results should be the next milestone in evaluating the safety of BPA substitutes and their halogenated transformation products.

Toxicity and Estrogenicity of Bisphenol TMC in Oryzias melastigma via In Vivo and In Silico Studies

Bisphenol 4-[1-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexyl] phenol (BPTMC), as a substitute for bisphenol A, has been detected in environments. However, the ecotoxicological data of BPTMC are extremely scarce. Here, the lethality, developmental toxicity, locomotor behavior, and estrogenic activity of BPTMC at different concentrations (0.25-2000 μg/L) in marine medaka (Oryzias melastigma) embryos were examined. In addition, the in silico binding potentials of O. melastigma estrogen receptors (omEsrs) with BPTMC were assessed by docking study. Low-concentration BPTMC exposure (including an environmentally relevant concentration, 0.25 μg/L) resulted in stimulating effects, including hatching rate, heart rate, malformation rate, and swimming velocity. However, elevated concentrations of BPTMC led to an inflammatory response, changed heart rate and swimming velocity in the embryos and larvae. In the meantime, BPTMC (including 0.25 μg/L) altered the concentrations of estrogen receptor, vitellogenin, and endogenous 17 β-estradiol as well as the transcriptional levels of estrogen-responsive genes in the embryos or/and larvae. Furthermore, elaborate tertiary structures of omEsrs were built by ab initio modeling, and BPTMC exerted potent binding potential with three omEsrs with -47.23, -49.23, and -50.30 kJ/mol for Esr1, Esr2a, and Esr2b, respectively. This work suggests that BPTMC has potent toxicity and estrogenic effects in O. melastigma.

The effects of endocrine-disrupting chemicals on ovarian- and ovulation-related fertility outcomes

Exposure to endocrine-disrupting chemicals (EDCs) is unavoidable, which represents a public health concern given the ability of EDCs to target the ovary. However, there is a large gap in the knowledge about the impact of EDCs on ovarian function, including the process of ovulation. Defects in ovulation are the leading cause of infertility in women, and EDC exposures are contributing to the prevalence of infertility. Thus, investigating the effects of EDCs on the ovary and ovulation is an emerging area for research and is the focus of this review. The effects of EDCs on gametogenesis, uterine function, embryonic development, and other aspects of fertility are not addressed to focus on ovarian- and ovulation-related fertility issues. Herein, findings from epidemiological and basic science studies are summarized for several EDCs, including phthalates, bisphenols, per- and poly-fluoroalkyl substances, flame retardants, parabens, and triclosan. Epidemiological literature suggests that exposure is associated with impaired fecundity and in vitro fertilization outcomes (decreased egg yield, pregnancies, and births), while basic science literature reports altered ovarian follicle and corpora lutea numbers, altered hormone levels, and impaired ovulatory processes. Future directions include identification of the mechanisms by which EDCs disrupt ovulation leading to infertility, especially in women.

High Content Imaging Analyses of the Effects of Bisphenols and Organophosphate Esters on TM4 Mouse Sertoli Cells

The endocrine disruptive effects of bisphenol A (BPA) and brominated flame retardants (BDE-47) have led to restrictions to their use and increased the pressure to identify safe replacements for these chemicals. Although there is evidence that some of these alternatives may be toxic to spermatogonial and Leydig cells, little is known about the toxicity of emerging replacements on Sertoli cells, one of the major testicular cell types. We used high-content imaging to compare the effects of legacy chemicals, BPA and BDE-47, to their corresponding replacements. TM4 Sertoli cells were exposed for 48 h to each chemical (0.001-100 μM) followed by cytotoxicity and phenotypic endpoint assessment. The benchmark concentration (BMC) potency ranking for bisphenols based on cytotoxicity was BPTMC>BPM > BPAF>BPF > BPS > BPA. Human administered equivalent dose (AED) determination ranked BPS as most potent alternative replacement studied. The BMC potency ranking of BDE-47 and organophosphate esters based on cytotoxicity was TDtBPP>BDMPP>TBOEP>TDCPP>TMPP>TPHP> BDE47 > IPPP=BPDP = TCPP. Additionally, TM4 cell exposure to BDE-47 increased Calcein intensity (57.9 μM) and affected lysosomes (21.6 μM), while exposure to TPHP and TMPP resulted in cellular oxidative stress changes at BMC values as low as 0.01 μM and 0.4 μM, respectively. Overall bioactivity considerations of the chemicals on TM4 via ToxPi analyses and AED modeling further validated emerging replacements as highly potent chemicals in comparison to BPA and BDE-47. These findings demonstrate that many bisphenol and flame retardant replacements are more potent in Sertoli cells than the legacy chemical they are replacing, and that phenotypic parameter assessment is an effective tool in chemical toxicity assessment.

Overlooked environmental risks deriving from aqueous transformation of bisphenol alternatives: Integration of chemical and toxicological insights

Owing to the widespread prevalence and ecotoxicity of bisphenol alternatives such as bisphenol S, bisphenol F, and bisphenol AF, the past decade has witnessed the publication of a remarkable number of studies related to their transformation and remediation in natural waters. However, the reactivity, removal efficiency, transformation products (TPs), and mechanisms of such emerging pollutants by different treatment processes have not been well elucidated. Particularly, the transformation-driven environmental risks have been mostly overlooked. Therefore, we present a review to address these issues from chemical and toxicological viewpoints. Four degradation systems can be largely classified as catalytic persulfate (PS) oxidation, non-catalytic oxidation, photolysis and photocatalysis, and biodegradation. It was found that bisphenol alternatives possess distinct reactivities with different oxidizing species, with the highest performance for hydroxyl radicals. All systems exhibit superior elimination efficiency for these compounds. The inadequate mineralization suggests the formation of recalcitrant TPs, from which the overall reaction pathways are proposed. The combined experimental and in silico analysis indicates that many TPs have developmental toxicity, endocrine-disrupting effects, and genotoxicity. Notably, catalytic PS systems and non-catalytic oxidation result in the formation of coupling products as well as halogenated TPs with higher acute and chronic toxicity and lower biodegradability than the parent compounds. In contrast, photolysis and photocatalysis generate hydroxylated and bond-cleavage TPs with less toxicity. Overall, this review highlights the secondary environmental risks from the transformation of bisphenol alternatives by conventional and emerging treatment processes. Finally, future perspectives are recommended to address the knowledge gaps of these contaminants in aquatic ecosystems.

The Effects of Organophosphate Esters Used as Flame Retardants and Plasticizers on Granulosa, Leydig, and Spermatogonial Cells Analyzed Using High-Content Imaging

The replacement of regulated brominated flame retardants and plasticizers with organophosphate esters (OPEs) has led to their pervasive presence in the environment and in biological matrices. Further, there is evidence that exposure to some of these chemicals is associated with reproductive toxicity. Using a high-content imaging approach, we assessed the effects of exposure to 9 OPEs on cells related to reproductive function: KGN human granulosa cells, MA-10 mouse Leydig cells, and C18-4 mouse spermatogonial cells. The effects of OPEs were compared with those of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a legacy brominated flame retardant. Alterations in several important cell features, including cell survival, mitochondrial dynamics, oxidative stress, lysosomes, and lipid droplets, were analyzed. Most of the OPEs tested displayed higher cytotoxicity than BDE-47 in all 3 cell lines. Effects on phenotypic parameters were specific for each cell type. Several OPEs increased total mitochondria, decreased lysosomes, increased the total area of lipid droplets, and induced oxidative stress in KGN cells; these endpoints were differentially affected in MA-10 and C18-4 cells. Alterations in cell phenotypes were highly correlated in the 2 steroidogenic cell lines for a few triaryl OPEs. Potency ranking using 2 complementary approaches, Toxicological Prioritization Index analyses and the lowest benchmark concentration/administered equivalent dose method, revealed that while most of the OPEs tested were more potent than BDE-47, others showed little to no effect. We propose that these approaches serve as lines of evidence in a screening strategy to identify the potential for reproductive and endocrine effects of emerging chemicals and assist in regulatory decision-making.

Implementing in vitro bioactivity data to modernize priority setting of chemical inventories

Internationally, there are thousands of existing and newly introduced chemicals in commerce, highlighting the ongoing importance of innovative approaches to identify emerging chemicals of concern. For many chemicals, there is a paucity of hazard and exposure data. Thus, there is a crucial need for efficient and robust approaches to address data gaps and support risk-based prioritization. Several studies have demonstrated the utility of in vitro bioactivity data from the ToxCast program in deriving points of departure (PODs). ToxCast contains data for nearly 1,400 endpoints per chemical, and the bioactivity concentrations, indicative of potential adverse outcomes, can be converted to human-equivalent PODs using high-throughput toxicokinetics (HTTK) modeling. However, data gaps need to be addressed for broader application: the limited chemical space of HTTK and quantitative high-throughput screening data. Here we explore the applicability of in silico models to address these data needs. Specifically, we used ADMET predictor for HTTK predictions and a generalized read-across approach to predict ToxCast bioactivity potency. We applied these models to profile 5,801 chemicals on Canada’s Domestic Substances List (DSL). To evaluate the approach’s performance, bioactivity PODs were compared with in vivo results from the EPA Toxicity Values database for 1,042 DSL chemicals. Comparisons demonstrated that the bioac­tivity PODs, based on ToxCast data or read-across, were conservative for 95% of the chemicals. Comparing bioactivity PODs to human exposure estimates supports the identification of chemicals of potential interest for further work. The bioac­tivity workflow shows promise as a powerful screening tool to support effective triaging of chemical inventories.

Phthalates and Alternative Plasticizers Differentially affect Phenotypic Parameters in Gonadal Somatic and Germ Cell Lines

The developmental and reproductive toxicity associated with exposure to phthalates has motivated a search for alternatives. However, there is limited knowledge regarding the adverse effects of some of these chemicals. We used high-content imaging to compare the effects of mono (2-ethylhexyl) phthalate (MEHP) with six alternative plasticizers: di-2-ethylhexyl terephthalate (DEHTP); diisononyl-phthalate (DINP); di-isononylcyclohexane-1,2-dicarboxylate (DINCH); 2-ethylhexyl adipate (DEHA); 2,2,4-trimethyl 1,3-pentanediol diisobutyrate (TXIB) and di-iso-decyl-adipate (DIDA). A male germ spermatogonial cell line (C18-4), a Sertoli cell line (TM4) and two steroidogenic cell lines (MA-10 Leydig and KGN granulosa) were exposed for 48h to each chemical (0.001-100 μM). Cell images were analyzed to assess cytotoxicity and effects on phenotypic endpoints. Only MEHP (100 μM) was cytotoxic and only in C18-4 cells. However, several plasticizers had distinct phenotypic effects in all four cell lines. DINP increased Calcein intensity in C18-4 cells, whereas DIDA induced oxidative stress. In TM4 cells, MEHP, and DINCH affected lipid droplet numbers, while DEHTP and DINCH increased oxidative stress. In MA-10 cells, MEHP increased lipid droplet areas and oxidative stress; DINP decreased the number of lysosomes, while DINP, DEHA and DIDA altered mitochondrial activity. In KGN cells, MEHP, DINP and DINCH increased the number of lipid droplets, whereas DINP decreased the number of lysosomes, increased oxidative stress and affected mitochondria. The Toxicological Priority Index (ToxPi) provided a visual illustration of the cell line specificity of the effects on phenotypic parameters. The lowest administered equivalent doses were observed for MEHP. We propose that this approach may assist in screening alternative plasticizers.