Bioactivation of Quinolines in a Recombinant Estrogen Receptor Transactivation Assay Is Catalyzed by N-Methyltransferases.

Hydroxylation of polyaromatic compounds through cytochromes P450 (CYPs) is known to result in potentially estrogenic transformation products. Recently, there has been an increasing awareness of the importance of alternative pathways such as aldehyde oxidases (AOX) or N-methyltransferases (NMT) in bioactivation of small molecules, particularly N-heterocycles. Therefore, this study investigated the biotransformation and activity of methylated quinolines, a class of environmentally relevant N-heterocycles that are no native ligands of the estrogen receptor (ER), in the estrogen-responsive cell line ERα CALUX. We found that this widely used cell line overexpresses AOXs and NMTs while having low expression of CYP enzymes. Exposure of ERα CALUX cells to quinolines resulted in estrogenic effects, which could be mitigated using an inhibitor of AOX/NMTs. No such mitigation occurred after coexposure to a CYP1A inhibitor. A number of N-methylated but no hydroxylated transformation products were detected using liquid chromatography-mass spectrometry, which indicated that biotransformations to estrogenic metabolites were likely catalyzed by NMTs. Compared to the natural ER ligand 17ß-estradiol, the products formed during the metabolization of quinolines were weak to moderate agonists of the human ERα. Our findings have potential implications for the risk assessment of these compounds and indicate that care must be taken when using in vitro estrogenicity assays, for example, ERα CALUX, for the characterization of N-heterocycles or environmental samples that may contain them.

Toward Streamlined Identification of Dioxin-like Compounds in Environmental Samples through Integration of Suspension Bioassay.

Effect-directed analysis (EDA) is a powerful strategy to identify biologically active compounds in environmental samples. However, in current EDA studies, fractionation and handling procedures are laborious, consist of multiple evaporation steps, and thus bear the risk of contamination and decreased recoveries of the target compounds. The low resulting throughput has been one of the major bottlenecks of EDA. Here, we propose a high-throughput EDA (HT-EDA) work-flow combining reversed phase high-performance liquid chromatography fractionation of samples into 96-well microplates, followed by toxicity assessment in the micro-EROD bioassay with the wild-type rat hepatoma H4IIE cells, and chemical analysis of bioactive fractions. The approach was evaluated using single substances, binary mixtures, and extracts of sediment samples collected at the Three Gorges Reservoir, Yangtze River, China, as well as the rivers Rhine and Elbe, Germany. Selected bioactive fractions were analyzed by highly sensitive gas chromatography-atmospheric pressure laser ionization-time-of-flight-mass spectrometry. In addition, we optimized the work-flow by seeding previously adapted suspension-cultured H4IIE cells directly into the microplate used for fractionation, which makes any transfers of fractionated samples unnecessary. The proposed HT-EDA work-flow simplifies the procedure for wider application in ecotoxicology and environmental routine programs.

Replacing animal-derived components in in vitro test guidelines OECD 455 and 487.

The evaluation of single substances or environmental samples for their genotoxic or estrogenic potential is highly relevant for human- and environment-related risk assessment. To examine the effects on a mechanism-specific level, standardized cell-based in vitro methods are widely applied. However, these methods include animal-derived components like fetal bovine serum (FBS) or rat-derived liver homogenate fractions (S9-mixes), which are a source of variability, reduced assay reproducibility and ethical concerns. In our study, we evaluated the adaptation of the cell-based in vitro OECD test guidelines TG 487 (assessment of genotoxicity) and TG 455 (detection of estrogenic activity) to an animal-component-free methodology. Firstly, the human cell lines A549 (for OECD TG 487), ERα-CALUX® and GeneBLAzer™ ERα-UAS-bla GripTite™ (for OECD TG 455) were investigated for growth in a chemically defined medium without the addition of FBS. Secondly, the biotechnological S9-mix ewoS9R was implemented in comparison to the induced rat liver S9 to simulate in vivo metabolism capacities in both OECD test guidelines. As a model compound, Benzo[a]pyrene was used due to its increased genotoxicity and endocrine activity after metabolization. The metabolization of Benzo[a]Pyrene by S9-mixes was examined via chemical analysis. All cell lines (A549, ERα-CALUX® and GeneBLAzer™ Erα-UAS-bla GripTite™) were successfully cultivated in chemically defined media without FBS. The micronucleus assay could not be conducted in chemically defined medium due to formation of cell clusters. The methods for endocrine activity assessment could be conducted in chemically defined media or reduced FBS content, but with decreased assay sensitivity. The biotechnological ewoS9R showed potential to replace rat liver S9 in the micronucleus in FBS-medium with A549 cells and in the ERα-CALUX® assay in FBS- and chemically defined medium. Our study showed promising steps towards an animal-component free toxicity testing. After further improvements, the new methodology could lead to more reproducible and reliable results for risk assessment.

Evidence of increased estrogenicity upon metabolism of Bisphenol F - Elucidation of the key metabolites.

The increasing concern over bisphenol A (BPA) has directed much attention toward bisphenol F (BPF) and bisphenol S (BPS) as BPA alternatives for the development of "BPA-free" products. Consequently, BPS and BPF were frequently detected in surface water, sediment, sewage effluent, indoor dust, and even in food and biological fluids in humans. Thus, environmental researches start to focus on the potential environmental risks of BPA alternatives. While the estrogenically active metabolites and the specific estrogenically active structure are still unknown. In this study, the MTT assay on acute cytotoxicity and the recombinant transactivation assay were carried out to determine whether BPF and BPS are suitable alternatives to BPA. Our results show that the cytotoxic and estrogenic activities of BPS and BPF are lower than those of BPA. However, after the addition of a rat liver homogenate to simulate mammal metabolism, BPF exhibited higher estrogenic activity than BPA. To identify the chemical structures and estrogen receptor binding affinities of active estrogenic metabolites, LC-MS, MetaPrint2D(-React), and VirtualToxLab were integrated. The observed results indicated that the para-hydroxylated BPF and BPF-OCH3 might have strong ER binding affinities. These results demonstrate that metabolization is important to consider upon investigating endocrine disruption of chemicals getting into contact with humans, such as in dental sealing or food packaging. Alternatives to potentially hazardous substances should be thoroughly tested prior to use.

Is a liver comparable to a liver? A comparison of different rat-derived S9-fractions with a biotechnological animal-free alternative in the Ames fluctuation assay.

Metabolism has to be considered during the toxicological assessment of chemical and environmental samples because it is an important process in the mammalian liver. It can be assessed in vitro via liver homogenates called S9-fractions, an external metabolic activation system. However, the external metabolic activation systems can vary greatly in their composition due to biological variations among individual animals and animal strains that the S9-fraction are derived as well as the differences in the production treatment. To gain more insight into these variances, three different but commonly used rat-derived S9-fractions were compared in the present study for their variance and performance with a reference compound in the Ames fluctuation assay with Salmonella typhimurium strains TA 98 and TA 100 according to ISO 11350. Severe shortcomings of conventional rat-derived S9-fractions were observed in the present study, such that S9-fractions differed significantly within the same rat strain and for different types of induction procedures in regards to the metabolic capability. An intrinsic mutagenic potential of the three rat-derived S9-fractions were identified in the Ames fluctuation assay with varying S9-fraction concentrations. To address some of the shortcomings of the animal-derived S9-fraction, the present study investigated the use and performance of a biotechnological, animal-free alternative, ewoS9R, in comparison to one of the rat-derived S9-fraction as the others showed a mutagenic potential themselves. Specifically, 12 different chemicals were used as a reference to determine if ewoS9R could serve as an adequate and more consistent replacement of traditional rat-derived metabolic activation systems: 8 pro-mutagenic compounds (i.e., require metabolic activation to show a mutagenic potential), one pro-mutagenic compound but not in the tested strains, one mutagenic compound without metabolic activation and two compounds that are equivocal in the literature. EwoS9R was evaluated as a promising approach in the Ames fluctuation assay with 5 compounds observed to have similar results with both rat-derived S9-fraction and ewoS9R (41%), for 3 compounds ewoS9R was a better metabolization system than the rat-derived S9-fraction (16%). Further research is necessary to determine the full potential of ewoS9R in comparison to rat-derived S9-fractions.

Using a high-throughput method in the micronucleus assay to compare animal-free with rat-derived S9.

This study presents a high-throughput (HTP) micronucleus assay in multi-well plates with an automated evaluation for risk assessment applications. The evaluation of genotoxicity via the micronucleus assays according to international guidelines ISO 21427-2 with Chinese hamster (Cricetulus griseus) V79 cells was the starting point to develop our methodology. A drawback of this assay is that it is very time consuming and cost intensive. Our HTP micronucleus assay in a 48-well plate format allows for the simultaneous assessment of five different sample-concentrations with additional positive, negative and solvent controls with six technical replicates each within a quarter of the time required for the equivalent evaluation using the traditional slide method. In accordance with the 3R principle, animal compounds should be replaced with animal-free alternatives. However, traditional cell culture-based methods still require animal derived compounds like rat-liver derived S9-fraction, which is used to simulate the mammalian metabolism in in vitro assays that do show intrinsic metabolization capabilities. In the present study, a recently developed animal-free biotechnological alternative (ewoS9R) was investigated in the new high-throughput micronucleus assay. In total, 12 different mutagenic or genotoxic chemicals were investigated to assess the potential use of the animal-free metabolization system (ewoS9R) in comparison to a common rat-derived product. Out of the 12 compounds, one compound did not induce micronuclei in any treatment and 2 substances showed a genotoxic potential without the need for a metabolization system. EwoS9R demonstrated promising potential for future applications as it shows comparable results to the rat-derived S9 for 6 of the 9 pro-genotoxic substances tested. The remaining 3 substances (2-Acetamidofluorene, Benzo[a]pyrene, Cyclophosphamide) were only metabolized by rat-derived S9. A potential explanation is that ewoS9R was investigated with an approx. 10-fold lower enzyme concentration and was only optimized for CYP1A metabolization that may be improved with a modified production procedure. Future applications of ewoS9R go beyond the micronucleus assay, but further research is necessary.

Optimization of a pre-metabolization procedure using rat liver S9 and cell-extracted S9 in the Ames fluctuation test.

Many environmental pollutants pose a toxicological hazard only after metabolic activation. In vitro bioassays using cell lines or bacteria have often no or reduced metabolic activity, which impedes their use in the risk assessment. To improve the predictive capability of in vitro assays, external metabolization systems like the liver S9 fraction are frequently combined with in vitro toxicity assays. While it is typical for S9 fractions that samples and testing systems are combined in the same exposure system, we propose to separate the metabolism step and toxicity measurement. This allows for a modular combination of metabolic activation by enzymes isolated from rat liver (S9) or a biotechnological alternative (ewoS9R) with in vitro bioassays that lack metabolic capacity. Benzo(a)pyrene and 2-aminoanthracene were used as model compounds to optimize the conditions for the S9 metabolic degradation/activation step. The Ames assay with Salmonella typhimurium strains TA98 and TA100 was applied to validate the set-up of decoupling the S9 activation/metabolism from the bioassay system. S9 protein concentration of 0.25 mgprotein/mL, a supplement of 0.13 mM NADPH and a pre-incubation time of 100 min are recommended for activation of samples prior to dosing them to in vitro bioassays using the regular dosing protocols of the respective bioassay. EwoS9R performed equally well as Moltox S9, which is a step forward in developing true animal-free in vitro bioassays. After pre-incubation with S9 fraction, chemicals induced bacteria revertants in both the TA98 and the TA100 assay as efficiently as the standard Ames assay. The pre-incubation of chemicals with S9 fraction could serve for a wide range of cellular in vitro assays to efficiently combine activation and toxicity measurement, which may greatly facilitate the application of these assays for chemical hazard assessment and monitoring of environmental samples.

p53 induction and cell viability modulation by genotoxic individual chemicals and mixtures.

The binding of the p53 tumor suppression protein to DNA response elements after genotoxic stress can be quantified by cell-based reporter gene assays as a DNA damage endpoint. Currently, bioassay evaluation of environmental samples requires further knowledge on p53 induction by chemical mixtures and on cytotoxicity interference with p53 induction analysis for proper interpretation of results. We investigated the effects of genotoxic pharmaceuticals (actinomycin D, cyclophosphamide) and nitroaromatic compounds (4-nitroquinoline 1-oxide, 3-nitrobenzanthrone) on p53 induction and cell viability using a reporter gene and a colorimetric assay, respectively. Individual exposures were conducted in the absence or presence of metabolic activation system, while binary and tertiary mixtures were tested in its absence only. Cell viability reduction tended to present direct correlation with p53 induction, and induction peaks occurred mainly at chemical concentrations causing cell viability below 80%. Mixtures presented in general good agreement between predicted and measured p53 induction factors at lower concentrations, while higher chemical concentrations gave lower values than expected. Cytotoxicity evaluation supported the selection of concentration ranges for the p53 assay and the interpretation of its results. The often used 80% viability threshold as a basis to select the maximum test concentration for cell-based assays was not adequate for p53 induction assessment. Instead, concentrations causing up to 50% cell viability reduction should be evaluated in order to identify the lowest observed effect concentration and peak values following meaningful p53 induction.

Characterisation of transcriptional responses to dioxins and dioxin-like contaminants in roach (Rutilus rutilus) using whole transcriptome analysis.

There is significant concern regarding the contamination of riverine sediments with dioxins and dioxin-like compounds (DLCs), including polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and some polycyclic aromatic hydrocarbons (PAHs). The majority of studies investigating the ecotoxicology of DLCs in fish have focused on a few standard model species. However, there is significant uncertainty as to whether these model species are representative of native river fish, particularly in Europe. In this study, the transcriptional responses following exposure to equipotent concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), PCB 156 or the dioxin-like PAH, benzo[k]fluoranthene (BkF), were investigated in juvenile roach (Rutilus rutilus), a fish species that constitutes a large proportion of the fish biomass in freshwater bodies throughout Europe. To this end, RNA sequencing analysis was used to comprehensively characterise the molecular mechanisms and pathways of toxicity of these DLCs. Whole transcriptome analyses using ClueGO software revealed that DLCs have the potential to disrupt a number of important processes, including energy metabolism, oogenesis, the immune system, apoptosis and the response to oxidative stress. However, despite using equipotent concentrations, there was very little conservation of the transcriptional responses observed in fish exposed to different DLCs. TCDD provoked significant specific changes in the levels of transcripts related to immunotoxicity and carbohydrate metabolism, while PCB 156 caused virtually no specific effects. Exposure to BkF affected the most diverse suite of molecular functions and biological processes, including blood coagulation, oxidative stress responses, unspecific responses to organic or inorganic substances/stimuli, cellular redox homeostasis and specific receptor pathways. To our knowledge, this is the first study of the transcriptome-wide effects of different classes of DLCs in fish. These findings represent an important step towards describing complete toxicity pathways of DLCs, which will be important in the context of informing risk assessments of DLC toxicity in native fish species.

Determination of the CYP1A-inducing potential of single substances, mixtures and extracts of samples in the micro-EROD assay with H4IIE cells.

This protocol describes a quantitative and robust 96-well-plate-reader-based assay for the measurement of ethoxyresorufin-O-deethylase (EROD) activity using the rat hepatoma cell line H4IIE. The assay can be used to determine the cytochrome P450 subfamily 1A (CYP1A)-inducing potential of single substances, as well as of mixtures and extracts of samples. It is based on the aryl hydrocarbon receptor (AhR)-mediated induction of cytochrome P450 enzymes (subfamily 1A) in cells after exposure to dioxins and dioxin-like compounds. One enzymatic reaction catalyzed by CYP1A is the deethylation of the exogenous substrate 7-ethoxyresorufin to the fluorescent product resorufin, which is measured as EROD activity in the assay. The CYP1A-inducing potential of a sample can be reliably quantified by comparing the EROD activity with the concentration-response curve of the standard substance 2,3,7,8-tetrachlorodibenzo-p-dioxin, which can be detected at concentrations down to the picogram per liter range. A researcher familiar with the procedure can process up to 160 samples with four wells each within 3 d. The series described uses four plates with three concentrations per sample, which can be easily scaled to accommodate different sample sizes.

Alfacalcidol reduces the number of fallers in a community-dwelling elderly population with a minimum calcium intake of more than 500 mg daily.

OBJECTIVES: To study the effect of alfacalcidol (1alpha(OH)D3) on fall risk in community-dwelling elderly men and women. DESIGN: Randomized, double-blind, placebo-controlled intervention trial. SETTING: Basel, Switzerland. PARTICIPANTS: Three hundred seventy-eight community-dwelling elderly (191 women/187 men). INTERVENTION: Participants were randomly assigned to receive 1 microg of alfacalcidol or matched placebo daily for 36 weeks. MEASUREMENTS: Serum 25-hydoxyvitamin D3 (25(OH) D,1,25-dihydroxyvitamin D3 (D-hormone), and intact parathormone (iPTH) levels were measured using radioimmunoassay at baseline and every 12 weeks. Numbers of fallers and falls were assessed using a questionnaire during each study site visit. Dietary calcium intake was assessed at baseline using a food frequency questionnaire. RESULTS: At baseline, participants had, on average, normal vitamin D and D-hormone serum levels. Over 36 weeks, alfacalcidol treatment was associated with fewer fallers (odds ratio (OR)=0.69, 95% confidence interval (CI)=0.41-1.16) than placebo. In a post hoc subgroups analysis by medians of total calcium intake, this reduction reached significance in alfacalcidol-treated subjects with a total calcium intake of more than 512 mg/d (OR=0.45, 95% CI=0.21-0.97, P=.042) but not in those who consumed less than 512 mg/d (OR=1.00, 95% CI= 0.47-2.11, P=.998). Alfacalcidol treatment was also, independent of total calcium intake, associated with a significant 37.9% reduction in iPTH serum levels (P<.0001). No cases of clinically relevant hypercalcemia were observed. CONCLUSION: Provided a minimal calcium intake of more than 512 mg/d, alfacalcidol treatment significantly and safely reduces number of fallers in an elderly community dwelling population.