Development and Application of a Novel Bioassay System for Dioxin Determination and Aryl Hydrocarbon Receptor Activation Evaluation in Ambient-Air Samples

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

Organic contaminants are ubiquitous in the environment, with mounting evidence unequivocally connecting them to aquatic toxicity, illness, and increased mortality, underscoring their substantial impacts on ecological security and environmental health. The intricate composition of sample mixtures and uncertain physicochemical features of potential toxic substances pose challenges to identify key toxicants in environmental samples. Effect-directed analysis (EDA), establishing a connection between key toxicants found in environmental samples and associated hazards, enables the identification of toxicants that can streamline research efforts and inform management action. Nevertheless, the advancement of EDA is constrained by the following factors: inadequate extraction and fractionation of environmental samples, limited bioassay endpoints and unknown linkage to higher order impacts, limited coverage of chemical analysis (i.e., high-resolution mass spectrometry, HRMS), and lacking effective linkage between bioassays and chemical analysis. This review proposes five key advancements to enhance the efficiency of EDA in addressing these challenges: (1) multiple adsorbents for comprehensive coverage of chemical extraction, (2) high-resolution microfractionation and multidimensional fractionation for refined fractionation, (3) robust in vivo/vitro bioassays and omics, (4) high-performance configurations for HRMS analysis, and (5) chemical-, data-, and knowledge-driven approaches for streamlined toxicant identification and validation. We envision that future EDA will integrate big data and artificial intelligence based on the development of quantitative omics, cutting-edge multidimensional microfractionation, and ultraperformance MS to identify environmental hazard factors, serving for broader environmental governance.

AhR Agonistic Components in Urban Particulate Matter Regulate Astrocytic Activation and Function

Exposure to atmospheric particulate matter (PM) has been found to accelerate the onset of neurological disorders via the induction of detrimental neuroinflammatory responses. To reveal how astrocytes respond to urban atmospheric PM stimulation, a commercially available standard reference material (SRM1648a) was tested in this study on the activation of rat cortical astrocytes. The results showed that SRM1648a stimulation induced both A1 and A2 phenotypes in astrocytes, as characterized by the exposure concentration-dependent increases in Fkbp5, Sphk1, S100a10, and Il6 mRNA levels. Studying the functional alterations of astrocytes indicated that the neurotrophic factors of Gdnf and Ngf were transcriptionally upregulated due to astrocytic A2-type activation. SRM1648a also promoted autonomous motility of astrocytes and elevated the expressions of chemokines. The aryl hydrocarbon receptor (AhR) agonistic components, such as polycyclic aromatic hydrocarbons (PAHs), were recognized to greatly contribute to SRM1648a-induced effects on astrocytes, which was confirmed by the attenuation of PM-disturbed astrocytic effects via AhR blockage. This study, for the first time, uncovered the direct regulation of urban atmospheric PM on astrocytic activation and function and traced the containing bioactive components (e.g., PAHs) with AhR agonistic activity. The findings provided new knowledge on understanding the ambiguous neurological disturbance from ambient fine PM pollution.

Exploring the adverse effects of 1,3,6,8-tetrabromo-9H-carbazole in atherosclerotic model mice by metabolomic profiling integrated with mechanism studies in vitro

Given its wide distribution in the environment and latent toxic effects, 1,3,6,8-tetrabromo-9H-carbazole (1368-BCZ) is an emerging concern that has gained increasing attention globally. 1368-BCZ exposure is reported to have potential cardiovascular toxicity. Although atherosclerosis is a cardiovascular disease and remains a primary cause of mortality worldwide, no evidence has been found regarding the impact of 1368-BCZ on atherosclerosis. Therefore, we aimed to explore the deleterious effects of 1368-BCZ on atherosclerosis and the underlying mechanisms. Serum samples from 1368-BCZ-treated atherosclerotic model mice were subjected to metabolomic profiling to investigate the adverse influence of the pollutant. Subsequently, the molecular mechanism associated with the metabolic pathway of atherosclerotic mice that was identified following 1368-BCZ exposure was validated in vitro. Serum metabolomics analysis revealed that 1368-BCZ significantly altered the tricarboxylic acid cycle, causing a disturbance in energy metabolism. In vitro, we further validated general markers of energy metabolism based on metabolome data: 1368-BCZ dampened adenosine triphosphate (ATP) synthesis and increased reactive oxygen species (ROS) production. Furthermore, blocking the aryl hydrocarbon receptor (AhR) reversed the high production of ROS induced by 1368-BCZ. It is concluded that 1368-BCZ decreased the ATP synthesis by disturbing the energy metabolism, thereby stimulating the AhR-mediated ROS production and presumably causing aggravated atherosclerosis. This is the first comprehensive study on the cardiovascular toxicity and mechanism of 1368-BCZ based on rodent models of atherosclerosis and integrated with in vitro models.

Application of a ready-to-use cell sensor for dioxins and dioxin-like compounds screening in foodstuffs

Dioxins and dioxin-like compounds (DLCs) in foodstuffs are closely related to human health. As China is the largest food-consuming country, there is a potentially large demand for screening bioassays that are rapid, cost-effective and capable of determining dioxins and DLCs in foodstuffs. CBG2.8D is a reporter gene-based recombinant cell sensor that was recently developed for determining dioxin and DLCs in ambient and seafood samples. In this study, we established a bioanalytical method with this ready-to-use cell sensor for the bioanalysis of dioxins and DLCs in different types of meat samples. Twenty-nine samples from three typical types of meat (beef, pork and fish) were collected and subjected to both instrumental analysis and a CBG2.8D bioassay. The intra- and inter-lab reproducibility of the bioassay was investigated and the coefficients of variation (CVs) were lower than 25%, suggesting that the cell sensor had a good reproducibility for the meat samples. Based on the correlation equation and coefficient obtained by comparing the data from the instrumental analysis and CBG2.8D bioassay, we found that this method had better performance with pork and fish than with beef. The compliance rate was also determined by comparing the results from the instrumental analysis and there were no false results for the pork and fish samples. Lastly, a complete operation procedure was summarized as a guideline for practical application. In conclusion, the CBG2.8D cell sensor exhibits excellent stability and is capable of screening dioxins and DLCs in meat samples.

Effect-directed analysis for revealing aryl hydrocarbon receptor agonists in sediment samples from an electronic waste recycling town in China

Exposure to electronic and electrical waste (e-waste) has been related to a few adverse health effects. In this study, sediment samples from an e-waste recycling town in China were collected, and aryl hydrocarbon receptor (AhR) agonists in the samples were identified using an effect-directed analysis (EDA) strategy. The CBG2.8D cell line reporter gene bioassay was used as a toxicity test, while suspect screening against chemical databases was performed for potential AhR agonist identification where both gas chromatography- and liquid chromatography-high resolution mass spectrometry analyses were run. When the original sample extract showed high AhR-mediated activity, sample fractionation was performed, and fractions exhibiting high bioactivity were chemically analyzed again to reveal the corresponding AhR agonists. In total, 23 AhR agonists were identified, including 14 commonly known ones and 9 new ones. Benzo [k]fluoranthene and 6-nitrochrysene were the dominant AhR agonists, covering 16-71% and 2.7-12%, respectively, of the AhR activation effects measured in the parent extracts. The newly identified AhR-active chemicals combined explained 0.13-0.20% of the parent extracts' effects, with 7,12-dimethylbenz [a]anthracene and 8,9,11-trimethylbenz [a]anthracene being the major contributors. A diagnostic isomer ratio analysis of polycyclic aromatic hydrocarbons suggested that the major source of AhR agonists identified in these e-waste related sediment samples were probably petroleum product combustion and biomass combustion. In the future, for a more comprehensive AhR agonist investigation, in-house chemical synthesis and purification, and, when necessary, a secondary sample fractionation, would be beneficial.

Multi-walled carbon nanotubes inhibit potential detoxification of dioxin-mediated toxicity by blocking the nuclear translocation of aryl hydrocarbon receptor

Despite numerous studies on effects of environmental accumulation of nano-pollutants, the influence of nanoparticles on the biological perturbations of coexisting pollutants in the environment remained unknown. The present study aimed at elucidating the perturbations of six environmental nanoparticles on detoxification of dioxin-induced toxicity at cellular level. We discovered that there was no remarkable difference in the cell uptake and intracellular distributions of these six nanoparticles. However, they have different effects on the detoxification of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). Multi-walled carbon nanotubes (MWCNTs) inhibited the translocation of aryl hydrocarbon receptor (AhR) from cytosol to the nucleus, leading to the downregulation of cytochrome P450 family 1 subfamily A member 1 (CYP1A1) and inhibition of detoxification function. These findings demonstrate that MWCNTs can impact the potential detoxification of dioxin-induced toxicity through modulating AhR signaling pathway. Co-exposures to MWCNTs and dioxin may cause even more toxicity than single exposure to dioxin or MWCNTs alone.

The aryl hydrocarbon receptor: A predominant mediator for the toxicity of emerging dioxin-like compounds

The aryl hydrocarbon receptor (AHR) is a member of the basic helix-loop-helix/Per-ARNT-Sim (bHLH-PAS) family of transcription factors and has broad biological functions. Early after the identification of the AHR, most studies focused on its roles in regulating the expression of drug-metabolizing enzymes and mediating the toxicity of dioxins and dioxin-like compounds (DLCs). Currently, more diverse functions of AHR have been identified, indicating that AHR is not just a dioxin receptor. Dioxins and DLCs occur ubiquitously and have diverse health/ecological risks. Additional research is required to identify both shared and compound-specific mechanisms, especially for emerging DLCs such as polyhalogenated carbazoles (PHCZs), polychlorinated diphenyl sulfides (PCDPSs), and others, of which only a few investigations have been performed at present. Many of the toxic effects of emerging DLCs were observed to be predominantly mediated by the AHR because of their structural similarity as dioxins, and the in vitro TCDD-relative potencies of certain emerging DLC congeners are comparable to or even greater than the WHO-TEFs of OctaCDD, OctaCDF, and most coplanar PCBs. Due to the close relationship between AHR biology and environmental science, this review begins by providing novel insights into AHR signaling (canonical and non-canonical), AHR's biochemical properties (AHR structure, AHR-ligand interaction, AHR-DNA binding), and the variations during AHR transactivation. Then, AHR ligand classification and the corresponding mechanisms are discussed, especially the shared and compound-specific, AHR-mediated effects and mechanisms of emerging DLCs. Accordingly, a series of in vivo and in vitro toxicity evaluation methods based on the AHR signaling pathway are reviewed. In light of current advances, future research on traditional and emerging DLCs will enhance our understanding of their mechanisms, toxicity, potency, and ecological impacts.

Transiently gene-modulated cell reporter for ultrasensitive detection of estrogen-like compounds in tap water

Abnormal elevation of indispensable steroid hormone estrogens and exposure to exogenous estrogen-like compounds pose adverse health effects to aquatic animals and human alike. These compounds generally display functionally important estrogenic activity even at extremely low picomolar concentrations. In this study we identified one critical but lethal gene (TAF1) that remarkably represses estrogenic activity. This gene is selected as a candidate for genetically modulating an estrogen-responding cell line. To overcome its lethality, instead of adopting a gene knockout strategy, we developed a transient TAF1 depletion strategy using a designed small interfering RNA. By the transient knockdown of TAF1 in the estrogen-responding reporter cell line, the maximum induction signals for endogenous estrogen 17β-estradiol (E2) and environmental estrogens 17α-ethynyl estradiol (EE2) and bisphenol compounds were enhanced by 4.8-13.3 folds. The limit of detection for EE2 is about 8 × 10^-15 mol/L. Moreover, by the established method, trace estrogenic activity (14.7-24.2 pg E2 equivalents (E2Eq)/L) can be detected in a portion of Tap water samples.

Rutaecarpine Inhibits U87 Glioblastoma Cell Migration by Activating the Aryl Hydrocarbon Receptor Signaling Pathway

Glioblastoma is the most frequent and aggressive primary astrocytoma in adults. The high migration ability of the tumor cells is an important reason for the high recurrence rate and poor prognosis of glioblastoma. Recently, emerging evidence has shown that the migration ability of glioblastoma cells was inhibited upon the activation of aryl hydrocarbon receptor (AhR), suggesting potential anti-tumor effects of AhR agonists. Rutaecarpine is a natural compound with potential tumor therapeutic effects which can possibly bind to AhR. However, its effect on the migration of glioblastoma is unclear. Therefore, we aim to explore the effects of rutaecarpine on the migration of human glioblastoma cells U87 and the involvement of the AhR signaling pathway. The results showed that: (i) compared with other structural related alkaloids, like evodiamine and dehydroevodiamine, rutaecarpine was a more potent AhR activator, and has a stronger inhibitory effect on the glioblastoma cell migration; (ii) rutaecarpine decreased the migration ability of U87 cells in an AhR-dependent manner; (iii) AhR mediated the expression of a tumor suppressor interleukin 24 (IL24) induced by rutaecarpine, and AhR-IL24 axis was involved in the anti-migratory effects of rutaecarpine on the glioblastoma. Besides IL24, other candidates AhR downstream genes both associated with cancer and migration were proposed to participate in the migration regulation of rutaecarpine by RNA-Seq and bioinformatic analysis. These data indicate that rutaecarpine is a naturally-derived AhR agonist that could inhibit the migration of U87 human glioblastoma cells mostly via the AhR-IL24 axis.

Evaluation of the dioxin-like toxicity in soil samples from Thua Thien Hue province using the AhR-CALUX bioassay - An update of Agent Orange contamination in Vietnam

In this study, an AhR-responsive reporter-gene cell-based bioassay CALUX was used to assess the biological potency of dioxins and dioxin-like PCBs (dl-PCBs) in top soil samples collected from a former airbase (A-So) and remote regions from urban and agricultural areas in Thua Thien Hue, Vietnam. In top soil collected from A-So airbase, Bioanalytical EQuivalent (BEQ) concentrations of up to 2700 pg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) per g dry weight (pg BEQ-TCDD g^-1 dw) were assessed. Interestingly, while BEQ values for dl-PCBs were found to be up to 13 pg BEQ-TCDD g^-1 dw, the dl-PCB activity was not detected in all the hotspot sample extracts. In contrasts, BEQ values for dioxin like compounds from remote regions were much lower and occasionally below the quantification limits of the method. The BEQ activities obtained in this study have a similar trend to the WHO-TEQ results for the samples collected in the A-So airbase. However, BEQ values were higher than those of TEQ, probably reflecting the presence of additional AhR ligands and/or possible non-additive interactions in the sample mixture. This study confirms that after more than 60 years, a strong residual pollution of PCDD/Fs remains on this former air base following the use and storage of Agent Orange during the Vietnam War, raising a health risk for populations exposed in this area because livestock animals graze there.

Simple and rapid determination of dioxin in fish and sea food using a highly sensitive reporter cell line, CBG 2.8D

Food, especially animal origin food is the main source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and dioxin-like polychlorinated biphenyls (dl-PCBs) for human exposure. So, a simple, rapid and cheap bioassay method is needed for determination of dioxins in food samples. In this study, we used a new highly sensitive reporter cell line to determine the concentration of dioxins in 33 fish and seafood samples. The samples were extracted by shaking with water/isopropanol (1:1 v/v) and hexane and cleaned-up by a multi layered silica gel column and an alumina column, then analyzed using CBG 2.8D cell line. We compared the results obtained from the CBG 2.8D cell assay to those obtained from conventional High-Resolution Gas Chromatography-High Resolution Mass Spectrometry (HRGC-HRMS) analysis. Good correlations were observed between these two methods (r²=0.93). While the slope of regression line was 1.76, the bioanalytical equivalent (BEQ) values were 1.76 folds higher than WHO-TEQ values and the conversion coefficient was 0.568 (the reciprocal of 1.76). In conclusion, CBG 2.8D cell assay was an applicable method to determine dioxins levels in fish and sea food samples.

Validation of the micro-EROD assay with H4IIE cells for assessing sediment contamination with dioxin-like chemicals

In vitro bioassays have been used as a bioanalytical means of detecting dioxin-like compounds (DLCs) in environmental matrices and have been suggested as a tool for quantifying DLCs in sediments. The present study evaluated the relationship between bioanalytical results from the micro-7-ethoxyresorufin-O-deethylase (EROD) bioassay and chemical analytical results in 25 sediment samples collected from rivers across Germany. Sediments were collected, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) were extracted from the sediments, biological toxicity equivalent quotients (BEQs) were determined by micro-EROD assay and toxicity equivalent quotients (TEQs) were calculated from chemical analysis. Correlations between BEQs and TEQs were evaluated, and linear regression modeling was performed, excluding 6 samples as validation data, to derive equations for predicting TEQs from BEQs. Validation data was tested to evaluate predictive capabilities of the models. Correlations were observed between BEQ and TEQ for PCDD/Fs (r=0.987), PCBs (r=0.623), measured sum of PCDD/F and PCBs (r = 0.975) and calculated sum of PCDD/F and PCBs (r = 0.971). The modeling equations provided low variances as evaluated by mean absolute error (MAE) (≤10.3 pg/g) and root mean square error (RMSE) (≤15.8 pg/g) indicating that expected TEQs could be reasonably well calculated from BEQs. Predicted TEQs from validation data fell within the 95% probability intervals of the test data and had low variances (MAE≤6.5 pg/g) and (RMSE≤10.7 pg/g). Our results indicate that the micro-EROD bioassay can be used as a screening tool for DLCs in sediment and has the capability to be used as an alternate method to chemical analysis for quantifying dioxin-like potential of sediments.

Identification of endogenous 1-aminopyrene as a novel mediator of progressive chronic kidney disease via aryl hydrocarbon receptor activation

BACKGROUND AND PURPOSE

Increasing evidence has indicated that the high risk of cardiovascular disease in chronic kidney disease (CKD) patients cannot be sufficiently explained by classic risk factors.

EXPERIMENTAL APPROACH

Based on the least absolute shrinkage and selection operator method, we identified significantly altered renal tissue metabolites during progressive CKD in a 5/6 nephrectomized rat model and in CKD patients.

KEY RESULTS

Six aryl-containing metabolites (ACMs) were significantly increased from Week 1 to Week 20. They were associated with the activation of aryl hydrocarbon receptor (AhR) and its target genes including CYP1A1, CYP1A2 and CYP1B1, which were further validated by molecular docking. Our study further demonstrated that AhR signalling could be activated by ACM in patients with idiopathic membranous nephropathy, diabetic nephropathy and IgA nephropathy. Most importantly, 1-aminopyrene (AP) showed strong positive and negative correlation with serum creatinine and creatinine clearance, respectively. AP significantly up-regulated the mRNA expressions of AhR and its three target genes in both mice and NRK-52E cells, while this effect was partially weakened in AhR small hairpin RNA-treated mice and NRK-52E cells. Furthermore, dietary flavonoid supplementation ameliorated CKD and renal fibrosis through partially inhibiting the AhR activity via lowering the ACM levels. The antagonistic effect of flavonoids on AhR was deeply influenced by the number and location of hydroxyl and glycosyl groups.

CONCLUSION AND IMPLICATIONS

We uncovered that endogenous AP is a novel mediator of CKD progression via AhR activation; thus, AhR might serve as a promising target for CKD treatment.

Regulation of Aryl Hydrocarbon Receptor Signaling Pathway and Dioxin Toxicity by Novel Agonists and Antagonists

Dioxins, mostly through activation of aryl hydrocarbon receptor (AhR), are potent toxic substances widely distributed in the environment, while moderated suppression of AhR also exhibits anti-tumor effects. Therefore, the proper modulation of AhR activity may counteract AhR-mediated toxicities and certain diseases. In this investigation, we identified several novel AhR moderate agonists and antagonists using chemical biology approaches. The mechanisms and mode of interactions with AhR by these hits were also revealed using both experimental and computational studies. The newly identified AhR moderate agonists and antagonists were predicted to bind to AhR and modulate AhR signaling. The structure-activity relationships of moderate agonists and antagonists and their unique binding features with AhR have created a solid framework for further optimization of the next generation of AhR modulators.

Characterization of the Aryl Hydrocarbon Receptor (AhR) Pathway in Anabas testudineus and Mechanistic Exploration of the Reduced Sensitivity of AhR2a

Field investigations have revealed the ability of the climbing perch Anabas testudineus to survive in highly contaminated water bodies. The aryl hydrocarbon receptor (AhR) pathway is vital in mediating the toxicity of aromatic hydrocarbon contaminants, and genotypic variation in the AhR can confer resistance to these contaminants. Thus, we characterized the AhR pathway in A. testudineus in order to understand the mechanism(s) underlying the resistance of this species to contaminants and to broaden current knowledge on teleost AhR. In A. testudineus, four AhRs, two AhR nuclear translocators (ARNTs), and one AhR repressor (AhRR) were found. Transient transfection assays revealed that AhR1a, AhR1b, and AhR2b were functional, whereas AhR2a was poorly activated by the potent agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Two ARNTs (partner of AhR) and one AhRR (repressor of AhR) all were functional with each of the active AhR. As a major form, the insensitivity of AhR2a might serve as a potential mechanism for A. testudineus' reduced sensitivity to severe contamination. We explored the key residues that may account for AhR2a's insensitivity in silico and then functionally validated them in vitro. Two sites (VCS_322-324, M₃₇₀) in its ligand-binding domain (LBD) were proved critical for its sensitivity to TCDD. This systematic exploration of the AhR pathway showed that most members have maintained their traditional functions as expected, whereas a nonfunctionalization event has occurred for AhR2a.

Aryl hydrocarbon receptor activity of polyhalogenated carbazoles and the molecular mechanism

Polyhalogenated carbazoles (PHCZs) are a class of contaminants identified with persistence and bioaccumulation property from previous studies. However, the toxic effect and mechanism of PHCZs are not fully understood. In this study, eleven PHCZs, including four chlorocarbazoles, four bromocarbazoles and two bromo/chlorocarbazoles were screened for their potential aryl hydrocarbon receptor (AhR) activity by using a dioxin responsive element-driven luciferase reporter assay. We found that nine PHCZs significantly activated AhR in a concentration-dependent manner. Their potencies of AhR activation were 1000 to 100,000 folds less than that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent AhR ligand. The relative AhR activation potency of the nine PHCZs followed the order 2,3,6,7-tetrachloro-9H-carbazole >2,7-dibromo-9H-carbazole >1,3,6-tribromo-9H-carbazole >1,3,6,8-tetrachloro-9H-carbazole >1,3,6,8-tetrabromo-9H-carbazole >1-bromo-3,6-dichloro-9H-carbazole >3,6-dibromo-9H-carbazole >3-bromo-9H-carbazole >1,8-dibromo-3,6-dichloro-9H-carbazole, which was partly in line with the induction of AhR-mediated CYP1A1 expression. In silico analysis indicated that the nine PHCZs could be docked into the same pocket as TCDD due to their high structural similarity. However, the shrunk size of the heterocyclic moieties in PHCZs relative to that in TCDD dramatically decreased the complex stability provided by inter-molecular interactions. Moreover, two distinguished docking poses adopted by the nine PHCZs were found, in which one was illustrated by 2367-CCZ and 27-BCZ while the other symbolized by TCDD and the left seven agonists. The differential antagonizing effects of CH223191 on PHCZ-induced AhR activity supported such pose differentiation. The present experimental and in silico data provide new direct evidence of PHCZ-AhR interaction which sheds light on AhR-associated toxicological study and risk assessment of PHCZs.

Bioassay system for the detection of aryl hydrocarbon receptor agonists in waterborne pesticides using zebrafish cyp1a1 promoter-luciferase recombinant hepatic cells

Currently used pesticides are widely distributed in surface water. Most of them are harmful to aquatic animals. In the present study, a novel recombinant hepatic cell line was developed for detecting the activity of aryl hydrocarbon receptor (AhR) agonists, and their potential bio-toxicity to aquatic animals was evaluated. First, HepG2 cells were stably transfected with a luciferase reporter plasmid containing a zebrafish (Danio rerio) cyp1a1 promoter with twelve copies of dioxin-responsive elements. The minimal detection limit was a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentration of 0.3 ng/L (equivalent to 0.93 pM). The AhR agonist activity of thirty-seven pesticides was screened by measuring luciferase expression in the recombinant cells. Four pesticides (ipconazole, mepanipyrim, quinoxyfen and pencycuron) significantly induced luciferase expression. Additionally, cells treated with these four pesticides increased the cyp1a1 mRNA expression level, which further confirmed that they are AhR agonists. In conclusion, for the first time, we developed recombinant hepatic cells with a luciferase reporter plasmid containing a modified zebrafish cyp1a1 promoter. The cyp1a1 promoter luciferase reporter cells can be used as a sensitive and specific model to screen AhR agonists among currently used pesticides in water, which could be beneficial for risk assessment in aquatic environments.

Contributions of City-Specific Fine Particulate Matter (PM2.5) to Differential In Vitro Oxidative Stress and Toxicity Implications between Beijing and Guangzhou of China

Growing literature has documented varying toxic potencies of source- or site-specific fine particulate matter (PM_2.5), as opposed to the practice that treats particle toxicities as independent of composition given the incomplete understanding of the toxicity of the constituents. Quantifying component-specific contribution is the key to unlocking the geographical disparities of particle toxicity from a mixture perspective. In this study, we performed integrated mixture-toxicity experiments and modeling to quantify the contribution of metals and polycyclic aromatic hydrocarbons (PAHs), two default culprit component groups of PM_2.5 toxicity, to in vitro oxidative stress caused by wintertime PM_2.5 from Beijing and Guangzhou, two megacities in China. PM_2.5 from Beijing exhibited greater toxic potencies at equal mass concentrations. The targeted chemical analysis revealed higher burden of metals and PAHs per unit mass of PM_2.5 in Beijing. These chemicals together explained 38 and 24% on average of PM_2.5-induced reactive oxygen species in Beijing and Guangzhou, respectively, while >60% of the effects remained to be resolved in terms of contributing chemicals. PAHs contributed approximately twice the share of the PM_2.5 mixture effects as metals. Fe, Cu, and Mn were the dominant metals, constituting >80% of the metal-shared proportion of the PM_2.5 effects. Dibenzo[ a, l]pyrene alone explained >65% of the PAH-shared proportion of the PM_2.5 toxicity effects. The significant contribution from coal combustion and vehicular emissions in Beijing suggested the major source disparities of toxicologically active PAHs between the two cities. Our study provided novel quantitative insights into the role of varying toxic component profiles in shaping the differential toxic potencies of city-specific PM_2.5 pollution.