Non-coplanar and coplanar polychlorinated biphenyls potentiate genotoxicity of aflatoxin B1 in a human hepatocyte line by enhancing CYP1A2 and CYP3A4 expression

Steatotic liver disease induced by TCPOBOP-activated hepatic constitutive androstane receptor: primary and secondary gene responses with links to disease progression

Constitutive androstane receptor (CAR, Nr1i3), a liver nuclear receptor and xenobiotic sensor, induces drug, steroid, and lipid metabolizing enzymes, stimulates liver hypertrophy and hyperplasia, and ultimately, hepatocellular carcinogenesis. The mechanisms linking early CAR responses to later disease development are poorly understood. Here we show that exposure of CD-1 mice to TCPOBOP (1,4-bis[2-(3,5-dichloropyridyloxy)]benzene), a halogenated xenochemical and selective CAR agonist ligand, induces pericentral steatosis marked by hepatic accumulation of cholesterol and neutral lipid, and elevated circulating alanine aminotransferase, indicating hepatocyte damage. TCPOBOP-induced steatosis was weaker in the pericentral region but stronger in the periportal region in females compared with males. Early (1 day) TCPOBOP transcriptional responses were enriched for CAR-bound primary response genes, and for lipogenesis and xenobiotic metabolism and oxidative stress protection pathways; late (2 weeks) TCPOBOP responses included many CAR binding-independent secondary response genes, with enrichment for macrophage activation, immune response, and cytokine and reactive oxygen species production. Late upstream regulators specific to TCPOBOP-exposed male liver were linked to proinflammatory responses and hepatocellular carcinoma progression. TCPOBOP administered weekly to male mice using a high corn oil vehicle induced carbohydrate-responsive transcription factor (MLXIPL)-regulated target genes, dysregulated mitochondrial respiratory and translation regulatory pathways, and induced more advanced liver pathology. Overall, TCPOBOP exposure recapitulates histological and gene expression changes characteristic of emerging steatotic liver disease, including secondary gene responses in liver nonparenchymal cells indicative of transition to a more advanced disease state. Upstream regulators of both the early and late TCPOBOP response genes include novel biomarkers for foreign chemical-induced metabolic dysfunction-associated steatotic liver disease.

Human CYP1A1-activated aneugenicity of aflatoxin B1 in mammalian cells and its combined effect with benzo(a)pyrene

Aflatoxin B1 (AFB1) is the most toxic mycotoxin and a proven human carcinogen that requires metabolic activation, known by cytochrome P450 (CYP) 1A2 and 3A4. Previous evidence showed that AFB1 is activated by human recombinant CYP1A1 expressed in budding yeast. Yet, the toxicity, in particular the genotoxicity of the reactive metabolites formed from AFB1 remains unclear. Humans could be exposed to both AFB1 and benzo(a)pyrene (BaP) simultaneously, thus we were interested in their combined genotoxic effects subsequent to metabolic activation by CYP1A1. In this study, molecular docking of AFB1 to human CYP1A1 indicated that AFB1 is valid as a substrate. In the incubations with AFB1 in human CYP1A1-expressed microsomes, AFM1 as a marking metabolite of AFB1 was detected. Moreover, AFB1 induced micronucleus formation in a Chinese hamster V79-derived cell line and in a human lung epithelial BEAS-2B cell line, both expressing recombinant human CYP1A1, V79-hCYP1A1 and 2B-hCYP1A1 cells, respectively. Immunofluorescence of centromere protein B stained micronuclei was dominant in AFB1-treated BEAS-2B cells exposed to AFB1, suggesting an aneugenic effect. Moreover, AFB1 elevated the levels of ROS, 8-OHdG, AFB1-DNA adduct, and DNA breaks in 2B-hCYP1A1 cells, compared with those in the parental BEAS-2B cells. Meanwhile, AFB1 increased CYP1A1, RAD51, and γ-H2AX protein levels in 2B-hCYP1A1 cells, which were attenuated by the CYP1A1 inhibitor bergamottin. Co-exposure of AFB1 with BaP increased 8-OHdG, RAD51, and γ-H2AX levels (indicating DNA damage). In conclusion, AFB1 could be activated by human CYP1A1 for potent aneugenicity, which may be further enhanced by co-exposure to BaP.

Impact of plastic-related compounds on the gene expression signature of HepG2 cells transfected with CYP3A4

The presence of plastic and microplastic within the oceans as well as in marine flora and fauna have caused a multitude of problems that have been the topic of numerous investigations for many years. However, their impact on human health remains largely unknown. Such plastic and microplastic particles have been detected in blood and placenta, underlining their ability to enter the human body. Plastics also contain other compounds, such as plasticizers, antioxidants, or dyes, whose impact on human health is currently being studied. Critical enzymes within the metabolism of endogenous molecules, especially of xenobiotics, are the cytochrome P450 monooxygenases (CYPs). Although their importance in maintaining cellular balance has been confirmed, their interactions with plastics and related products are poorly understood. In this study, the possible relationship between different plastic-related compounds and CYP3A4 as one of the most important CYPs was analyzed using hepatic cells overexpressing this enzyme. Beginning with virtual compound screening and molecular docking of more than 1000 plastic-related compounds, several candidates were identified to interact with CYP3A4. In a second step, RNA-sequencing was used to study in detail the transcriptome-wide gene expression levels affected by the selected compounds. Three candidate molecules ((2,2'-methylenebis(6-tert-butyl-4-methylphenol), 1,1-bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethane, and 2,2'-methylenebis(6-cyclohexyl-4-methylphenol)) had an excellent binding affinity to CYP3A4 in-silico as well as cytotoxic effects and interactions with several metabolic pathways in-vitro. We identified common pathways influenced by all three selected plastic-related compounds. In particular, the suppression of pathways related to mitosis and 'DNA-templated DNA replication' which were confirmed by cell cycle analysis and single-cell gel electrophoresis. Furthermore, several mis-regulated metabolic and inflammation-related pathways were identified, suggesting the induction of hepatotoxicity at different levels. These findings imply that these compounds may cause liver problems subsequently affecting the entire organism.

Hepatoprotective effects of a chemically-characterized extract from artichoke (Cynara scolymus L.) against AFB1-induced toxicity in rats

This study was conducted to investigate the protective potential of a pharmaceutically formulated capsule of artichoke leaf powder (ArLP) against aflatoxin B1 (AFB1)-induced hepatotoxicity in male albino rats. In the 42-day experiment, rats were divided into five equal groups: (i) control, treated with sterile water, (ii) treated with 4% DMSO as AFB1 vehicle, (iii) ArLP of 100 mg kg-1 bw, (iv) AFB1 of 72 µg kg-1 bw, and (v) AFB1 plus ArLP. Exposure of rats to AFB1 resulted in hepatotoxicity as manifested by the intensification of oxidative stress, production of free radicals and significant increase in the activity levels of liver function enzymes relative to the control. Significant reductions in both the enzymatic and non-enzymatic antioxidant markers as well as histopathological abnormalities in liver tissues were also observed. Notably, the combined administration of ArLP with AFB1 clearly reduced AFB1-mediated adverse effects leading to the normalization of most of these parameters back to control levels. These findings clearly highlight the potential benefits of artichoke dietary supplements as a safe and natural solution in counteracting the adverse hepatotoxic effects conferred by AFB1 exposure. Further research is warranted to fully dissect the biochemical and molecular mechanism of action of the observed artichoke-mediated hepatoprotection.

Identification of PCB congeners and their thresholds associated with diabetes using decision tree analysis

Few studies have investigated the potential combined effects of multiple PCB congeners on diabetes. To address this gap, we used data from 1244 adults in the National Health and Nutrition Examination Survey (NHANES) 2003-2004. We used (1) classification trees to identify serum PCB congeners and their thresholds associated with diabetes; and (2) logistic regression to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of diabetes with combined PCB congeners. Of the 40 PCB congeners examined, PCB 126 has the strongest association with diabetes. The adjusted OR of diabetes comparing PCB 126 > 0.025 to ≤ 0.025 ng/g was 2.14 (95% CI 1.30-3.53). In the subpopulation with PCB 126 > 0.025 ng/g, a lower PCB 101 concentration was associated with an increased risk of diabetes (comparing PCB 101 < 0.72 to ≥ 0.72 ng/g, OR 3.3, 95% CI 1.27-8.55). In the subpopulation with PCB 126 > 0.025 & PCB 101 < 0.72 ng/g, a higher PCB 49 concentration was associated with an increased risk of diabetes (comparing PCB 49 > 0.65 to ≤ 0.65 ng/g, OR 2.79, 95% CI 1.06-7.35). This nationally representative study provided new insights into the combined associations of PCBs with diabetes.

The Effect of Plastic-Related Compounds on Transcriptome-Wide Gene Expression on CYP2C19-Overexpressing HepG2 Cells

In recent years, plastic and especially microplastic in the oceans have caused huge problems to marine flora and fauna. Recently, such particles have also been detected in blood, breast milk, and placenta, underlining their ability to enter the human body, presumably via the food chain and other yet-unknown mechanisms. In addition, plastic contains plasticizers, antioxidants, or lubricants, whose impact on human health is also under investigation. At the cellular level, the most important enzymes involved in the metabolism of xenobiotic compounds are the cytochrome P450 monooxygenases (CYPs). Despite their extensive characterization in the maintenance of cellular balance, their interactions with plastic and related products are unexplored. In this study, the possible interactions between several plastic-related compounds and one of the most important cytochromes, CYP2C19, were analyzed. By applying virtual compound screening and molecular docking to more than 1000 commercially available plastic-related compounds, we identified candidates that are likely to interact with this protein. A growth inhibition assay confirmed their cytotoxic activity on a CYP2C19-transfected hepatic cell line. Subsequently, we studied the effect of the selected compounds on the transcriptome-wide gene expression level by conducting RNA sequencing. Three candidate molecules were identified, i.e., 2,2'-methylene bis(6-tert-butyl-4-methylphenol), 1,1-bis(3,5-di-tert-butyl-2-hydroxyphenyl) ethane, and 2,2'-methylene bis(6-cyclohexyl-4-methylphenol)), which bound with a high affinity to CYP2C19 in silico. They exerted a profound cytotoxicity in vitro and interacted with several metabolic pathways, of which the 'cholesterol biosynthesis process' was the most affected. In addition, other affected pathways involved mitosis, DNA replication, and inflammation, suggesting an increase in hepatotoxicity. These results indicate that plastic-related compounds could damage the liver by affecting several molecular pathways.

Identification of PCB Congeners and their Thresholds associated with Diabetes using Decision Tree Analysis

Few studies have investigated the potential combined effects of multiple PCB congeners on diabetes. To address this gap, we used data from 1244 adults in the National Health and Nutrition Examination Survey (NHANES) 2003-2004. We used 1) classification trees to identify serum PCB congeners and their thresholds associated with diabetes; and 2) logistic regression to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of diabetes with combined PCB congeners. Of the 40 PCB congeners examined, PCB 126 has the strongest association with diabetes. The adjusted OR of diabetes comparing PCB 126 > 0.025 to ≤ 0.025 ng/g was 2.14 (95% CI 1.30-3.53). In the subpopulation with PCB 126 > 0.025 ng/g, a lower PCB 101 concentration was associated with an increased risk of diabetes (comparing PCB 101 < 0.72 to ≥ 0.72 ng/g, OR = 3.3, 95% CI: 1.27-8.55). In the subpopulation with PCB 126 > 0.025&PCB 101 < 0.72 ng/g, a higher PCB 49 concentration was associated with an increased risk of diabetes (comparing PCB 49 > 0.65 to ≤ 0.65 ng/g, OR = 2.79, 95% CI: 1.06-7.35). This nationally representative study provided new insights into the combined associations of PCBs with diabetes.

Human CYP1B1 enzyme-mediated, AhR enhanced activation of aflatoxin B1 for its genotoxicity in human cells

Aflatoxin B1 (AFB1) is a human procarcinogen known to be activated by cytochrome P450 (CYP) 1A2 and 3A4. In a previous study AFB1 caused chromosomal rearrangement in a yeast strain genetically engineered for stably expressing human CYP1B1. Yet, further verification of the effect of AFB1 in human cells, a potential role of the aryl hydrocarbon receptor (AhR), and CYP1B1-catalyzed AFB1 metabolism remain unidentified. In this study, a human hepatocyte (L-02) line and a human lymphoblastoid (TK6) cell line were genetically engineered for the expression of human CYP1B1, producing L-02-hCYP1B1 and TK6-hCYP1B1, respectively. They were exposed to AFB1 and analyzed for the formation of micronucleus and elevation of γ-H2AX (indicating double-strand DNA breaks); the metabolites formed by CYP1B1 from AFB1 after incubation of AFB1 with human CYP1B1 isoenzyme microsomes were determined by LC-MS. The results showed significantly more potent induction of micronucleus by AFB1 in L-02-hCYP1B1 and TK6-hCYP1B1 than in the parental (L-02 and TK6) cells, and the effects were reduced by (E)- 2,3',4,5'-tetramethoxystilbene, a specific CYP1B1 inhibitor. In the AFB1- CYP1B1 microsomes incubations AFM1, a known stable metabolite of AFB1, was detected. Moreover, in L-02 and TK6 cells, AFB1 apparently increased the protein levels of AhR, ANRT and CYP1B1, and caused the nuclear translocation of AhR and ARNT, the latter effect being blocked by BAY-218 (an inhibitor of AhR). In conclusion, this study indicates that human CYP1B1 is capable of metabolically activating AFB1 through the AhR signaling pathway.

Triphenyl phosphate induces clastogenic effects potently in mammalian cells, human CYP1A2 and 2E1 being major activating enzymes

As a new-type flame retardant and toxic substance, triphenyl phosphate (TPP) is a ubiquitous pollutant present even in human blood. TPP is transformed by human CYP enzymes to oxidized/dealkylated metabolites. The impact of TPP metabolism on its toxicity, however, remains unclear. In this study, the genotoxicity of TPP in several mammalian cell lines and its relevance to CYP/sulfortransferase (SULT) activities were investigated. The results indicated that TPP induced micronucleus formation at ≥1 μM concentrations in a human hepatoma (C3A, endogenous CYPs being substantial) cell line, which was abolished by 1-aminobenzotriazole (CYPs inhibitor). In cell line HepG2 (parental to C3A with lower CYP expression) TPP was inactive up to 10 μM, while pretreatment with ethanol (CYP2E1 inducer), PCB 126 (CYP1A inducer), or rifampicin (CYP3A inducer) led to micronucleus formation by TPP. In V79-Mz and V79-derived cells expressing human CYP1A1 TPP was inactive (up to 32 μM), and in cells expressing human CYP1B1, 2B6 and 3A4 it induced micronucleus weakly (positive only at 32 μM). However, TPP induced micronucleus potently in V79-derived cells expressing human CYP1A2, while this effect was drastically reduced by human SULT1A1 co-expression; likewise, TPP was inactive in cells expressing both human CYP2E1 and SULT1A1, but became positive with pentachlorophenol (inhibitor of SULT1) co-exposure. Moreover, in C3A cells TPP selectively induced centromere-free micronucleus (immunofluorescent assay), and TPP increased γ-H2AX (by Western blot, indicating double-strand DNA breaks). In conclusion, this study suggests that TPP is potently clastogenic, human CYP1A2 and 2E1 being major activating enzymes while SULT1A1 involved in detoxification.

Polluting characteristics, sources, cancer risk, and cellular toxicity of PAHs bound in atmospheric particulates sampled from an economic transformation demonstration area of Dongguan in the Pearl River Delta, China

The Songshan Lake Science and Technology Industrial Park is a national economic transition demonstration area, which centers at a traditional industrial region, in Dongguan, China. We were interested in the involved atmospheric particulates-bound PAHs regarding their sources, cancer risk, and related cellular toxicity for those in other areas under comparable conditions. In this study, the daily concentrations of TSP, PM₁₀, and PM_2.5 were averaged 127.95, 95.91, and 67.62 μg/m³, and the bound PAHs were averaged 1.31, 1.22, and 0.77 ng/m³ in summer and 12.72, 20.51 and 40.27 ng/m³ in winter, respectively. The dominant PAHs were those with 5-6 rings, and 4-6 rings in summer and winter, respectively. The incremental lifetime cancer risk (ILCR) (90th percentile probability) of total PAHs was above 1.00E-06 in each age group, particularly high in adolescents. Sensitivity analysis indicated that slope factor and body weight had greater impact than exposure duration and inhalation rate on the ILCR. Moreover, treatment of human bronchial epithelial BEAS-2B cells with mixed five indicative PAHs increased the formation of ROS, DNA damage (elevation in γ-H2AX), and protein levels of CAR, PXR, CYP1A1, 1A2, 1B1, while reduced the AhR protein, with the winter mixture more potent than summer. For the sources of PAHs, the stable carbon isotope ratio analysis and diagnostic ratios consistently pointed to petroleum and fossil fuel combustion as major sources. In conclusion, our findings suggest that particulates-bound PAHs deserve serious concerns for a cancer risk in such environment, and the development of new power sources for reducing fossil fuel combustion is highly encouraged.

Microcystin-LR-induced nuclear translocation of cGAS promotes mutagenesis in human hepatocytes by impeding homologous recombination repair

Microcystin-LR (MC-LR) has been recognized as a typical hepatotoxic cyclic peptides produced by cyanobacteria. Nowadays, due to the frequent occurrence of cyanobacterial blooms, the underlying hepatotoxic mechanism of MC-LR has become the focus of attention. In our present work, the mutagenic effect of MC-LR on human normal hepatic (HL-7702) cells regulated by cGAS was mainly studied. Here, we showed that exposure to MC-LR for 1-4 days could activate the cGAS-STING signaling pathway and then trigger immune response in HL-7702 cells. Notably, relative to the treatment with 1 μM MC-LR for 1-3 days, it was observed that when HL-7702 cells were exposed to 1 μM MC-LR for 4 days, the mutation frequency at the Hprt locus was remarkably increased. In addition, cGAS in HL-7702 cells was also found to complete the nuclear translocation after 4-day exposure. Moreover, co-immunoprecipitation and homologous recombination (HR)-directed DSB repair assay were applied to show that homologous recombination repair was inhibited after 4-day exposure. However, the intervention of the nuclear translocation of cGAS by transfecting BLK overexpression plasmid restored homologous recombination repair and reduced the mutation frequency at the Hprt locus in HL-7702 cells exposed to MC-LR. Our study unveiled the distinct roles of cGAS in the cytoplasm and nucleus of human hepatocytes as well as potential mutagenic mechanism under the early and late stage of exposure to MC-LR, and provided a novel insight into the prevention and control measures about the hazards of cGAS-targeted MC-LR.

Influence of aryl hydrocarbon receptor and sulfotransferase 1A1 on bisphenol AF-induced clastogenesis in human hepatoma cells

Bisphenol compounds (BPs) are ubiquitously existing pollutants. Recent evidence shows that they may be activated by human CYP1A1 for clastogenic effects; however, factors that influence/mediate CYP1A1-activated 4,4'-(hexafluoroisopropylidene)diphenol (BPAF) toxicity, particularly the aryl hydrocarbon receptor (AhR), sulfotransferase (SULT) 1A1 [known to conjugate 2,2-bis(4-hydroxyphenol)-propane (BPA)] and reactive oxygen species (ROS), remain unclear. In this study, a human hepatoma (HepG2) cell line was genetically engineered for the expression of human CYP1A1 and SULT1A1, producing HepG2-hCYP1A1 and HepG2-hSULT1A1, respectively. They were used in the micronucleus test and γ-H2AX analysis (Western blot) (indicating double-strand DNA breaks) with BPAF; the role of AhR in mediating BPAF toxicity was investigated by coexposure of AhR modulators in HepG2 and its derivative C3A (with no genetic modifications but enhanced CYP expression). The results indicated induction of micronuclei by BPAF (≥ 2.5 µM, for 2-cell cycle) in HepG2-hCYP1A1 and C3A, while inactive in HepG2 and HepG2-hSULT1A1; however, BPAF induced micronuclei in HepG2 pretreated with 3,3',4,4',5-pentachlorobiphenyl (PCB126, AhR activator), and BAY-218 (AhR inhibitor) blocked the effect of BPAF in C3A. In HepG2-hCYP1A1 BPAF selectively induced centromere-free micronuclei (immunofluorescent assay) and double-strand DNA breaks. In HepG2 cells receiving conditional medium from BPAF-HepG2-hCYP1A1 incubation micronuclei were formed, while negative in HepG2-hSULT1A1. Finally, the intracellular levels of ROS, superoxide dismutase and reduced glutathione in C3A and HepG2-hCYP1A1 exposed to BPAF were all moderately increased, while unchanged in HepG2 cells. In conclusion, like other BPs BPAF is activated by human CYP1A1 for potent clastogenicity, and this effect is enhanced by AhR while alleviated by SULT1A1.

Human CYP enzyme-activated genotoxicity of 2,2',4,4'-tetrabromobiphenyl ether in mammalian cells

Polybrominated biphenyl ethers (PBDEs) are a group of persistent organic pollutants with endocrine-disrupting, neurotoxic, tumorigenic and DNA-damaging activities. They are hydroxylated by human liver microsomal CYP enzymes, however, their mutagenicity remains unknown. In this study, 2,2',4,4'-tetrabromobiphenyl ether (BDE-47, relatively abundant in human tissues) was investigated for micronuclei induction and DNA damage in mammalian cells. The results indicated that BDE-47 up to 80 μM under a 6 h/18 h (exposure/recovery, covering 2 cell cycles) regime did not induce micronuclei in V79-Mz and V79-derived cell lines expressing human CYP1A1 or 1A2, while it was moderately positive in human CYP2B6-, 2E1-and 3A4-expressing cell lines (V79-hCYP2B6, V79-hCYP2E1-hSULT1A1 and V79-hCYP3A4-hOR, respectively). Following 24 h exposure, BDE-47 induced micronuclei in V79-hCYP2E1-hSULT1A1 and V79-hCYP3A4 cells at increased potencies. In the human hepatoma (HepG2) cells BDE-47 (48 h exposure) was inactive up to 40 μM, however, pretreatment of the cells with ethanol (0.2%, v:v, inducer of CYP2E1) or rifampicin (10 μM, inducer of CYP3A4) led to significant micronuclei formation by BDE-47; pretreatment with bisphenol AF (100 nM) also potentiated BDE-47-induced micronuclei formation (which was blocked by a CYP2E1 inhibitor trans-1,2-dichloroethylene or a CYP3A inhibitor (ketoconazole). Immunofluorescent staining of centromere protein B with the micronuclei formed by BDE-47 in HepG2 cells pretreated with ethanol or rifampicin demonstrated selective formation of centromere-containing micronuclei. The increased phosphorylation of both histones H2AX and H3 in HepG2 by BDE-47 also indicated an aneugenic potential. Therefore, this study suggests that BDE-47 is an aneugen activated by several human CYP enzymes.

MicroRNA regulates the toxicological mechanism of four mycotoxins in vivo and in vitro

Mycotoxins can cause body poisoning and induce carcinogenesis, often with a high mortality rate. Therefore, it is of great significance to seek new targets that indicate mycotoxin activity and to diagnose and intervene in mycotoxin-induced diseases in their early stages. MicroRNAs (miRNAs) are physiological regulators whose dysregulation is closely related to the development of diseases. They are thus important markers for the occurrence and development of diseases. In this review, consideration is given to the toxicological mechanisms associated with four major mycotoxins (ochratoxin A, aflatoxin B1, deoxynivalenol, and zearalenone). The roles that miRNAs play in these mechanisms and the interactions between them and their target genes are explained, and summarize the important role of histone modifications in their toxicity. As a result, the ways that miRNAs are regulated in the pathogenicity signaling pathways are revealed which highlights the roles played by miRNAs in preventing and controlling the harmful effects of the mycotoxins. It is hoped that this review will provide a theoretical basis for the prevention and control of the damage caused by these mycotoxins.

Assessment of binding potencies of polychlorinated biphenyls and polybrominated diphenyl ethers with Baikal seal and mouse constitutive androstane receptors: Comparisons across species and congeners

The present study evaluated the binding potencies (equilibrium dissociation constant: K_D) of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) with the constitutive androstane receptor (CAR)_ligand binding domain (LBD) of the Baikal seal (bsCAR_LBD) and mouse (mCAR_LBD) using a surface plasmon resonance (SPR) biosensor. The binding affinities of individual congeners with mCAR_LBD tended to be higher than those with bsCAR_LBD but the differences were within the same order of magnitude. Notably, PBDE congeners showed higher binding affinities for both CAR_LBDs than PCB congeners. In silico docking simulations demonstrated that PBDEs had more non-covalent interactions with specific amino acid residues in both CAR_LBDs than PCBs, supporting the results of their binding affinities. Binding affinity comparisons among congeners revealed the structural requirements for higher binding; mono or di ortho-, tri meta-, and di para‑chlorine substitutions for PCBs, and di or tri ortho-, mono meta-, and di para‑bromine substitutions for PBDEs. The binding potencies of these congeners unlikely accounted for their previously reported CAR-mediated transactivation potencies, implying that their transactivation is regulated in a ligand-dependent, but a distinct manner from ligand binding. Risk assessment analysis showed that the K_D values of individual PCB and PBDE congeners were 1-4 orders of magnitude higher than their respective hepatic concentrations in wild Baikal seal population.

Aflatoxin B1: metabolism, toxicology, and its involvement in oxidative stress and cancer development

Aflatoxins are a class of carcinogenic mycotoxins produced by Aspergillus fungi, which are widely distributed in nature. Aflatoxin B1 (AFB1) is the most toxic of these compounds and its metabolites have a variety of biological activities, including acute toxicity, teratogenicity, mutagenicity and carcinogenicity, which has been well-characterized to lead to the development of hepatocellular carcinoma (HCC) in humans and animals. This review focuses on the metabolism of AFB1, including epoxidation and DNA adduction, as it concerns the initiation of cancer and the underlying mechanisms. In addition to DNA adduction, inflammation and oxidative stress caused by AFB1 can also participate in the occurrence of cancer. Therefore, the main carcinogenic mechanism of AFB1 related ROS is summarized. This review also describes recent reports of AFB1 exposures in occupational settings. It is hoped that people will pay more attention to occupational health, in order to reduce the incidence of cancer caused by occupational exposure.

Human CYP enzyme-activated clastogenicity of 2-ethylhexyl diphenyl phosphate (a flame retardant) in mammalian cells

2-Ethylhexyl diphenyl phosphate (EHDPP) is a common flame retardant and environmental pollutant, exposing humans with endocrinal disrupting potentials. Its mutagenicity, especially following metabolism, remains unclear. In this study, molecular docking analysis indicated that EHDPP was a potential substrate for several human CYP enzymes except for CYP1A1. Among V79-derived cell lines genetically engineered for the expression of each CYP, EHDPP (6 h exposure/18 h recovery) did not induce micronuclei in the V79 or V79-derived cells expressing human CYP1A1, however, it was positive in V79-derived cell lines expressing human CYP2E1, 3A4, and 2B6. In a human hepatoma (HepG2) cell line, EHDPP (48 h exposure) moderately induced micronuclei, which was blocked by 1-aminobenzotriazole (ABT, 60 μM, inhibitor of CYPs); pretreating HepG2 cells with bisphenol AF, another organic pollutant as inducer of CYPs (0.1 μM for 16 h), significantly potentiated micronuclei formation by EHDPP, threshold being decreased from 10 to 1.25 μM. This effect was blocked by ABT, drastically reduced by ketoconazole (inhibiting CYP3A expression/activity), and moderately inhibited by trans-1,2-dichloroethylene (selective CYP2E1 inhibitor). Immunofluorescent centromere protein B staining indicated that EHDPP-induced micronuclei in V79-derived cell lines expressing human CYP2E1 and 3A4 were predominantly centromere-negative, and that in HepG2 cells pretreated with bisphenol AF (for inducing multiple CYPs) were purely centromere-negative. In bisphenol AF-pretreated HepG2 cells EHDPP potently induced DNA breaks, as indicated by the comet assay and Western blot analysis of γ-H2AX. In conclusion, our study suggests that EHDPP is potently clastogenic, following activation by several human CYP enzymes, CYP3A4 being a major one.

Impact of Estrogen Withdrawal and Replacement in Female Mice along the Intestinal Tract. Comparison of E2 Replacement with the Effect of a Mixture of Low Dose Pollutants

Postmenopausal women represent a vulnerable population towards endocrine disruptors due to hormonal deficit. We previously demonstrated that chronic exposure of ovariectomized C57Bl6/J mice fed a high-fat, high-sucrose diet to a low-dose mixture of chemicals with one dioxin, one polychlorobiphenyl, one phthalate, and bisphenol A triggered metabolic alterations in the liver but the intestine was not explored. Yet, the gastrointestinal tract is the main route by which pollutants enter the body. In the present study, we investigated the metabolic consequences of ovarian withdrawal and E2 replacement on the various gut segments along with investigating the impact of the mixture of pollutants. We showed that genes encoding estrogen receptors (Esr1, Gper1 not Esr2), xenobiotic processing genes (e.g., Cyp3a11, Cyp2b10), and genes related to gut homeostasis in the jejunum (e.g., Cd36, Got2, Mmp7) and to bile acid biosynthesis in the gut (e.g., Fgf15, Slc10a2) and liver (e.g., Abcb11, Slc10a1) were under estrogen regulation. Exposure to pollutants mimicked some of the effects of E2 replacement, particularly in the ileum (e.g., Esr1, Nr1c1) suggesting that the mixture had estrogen-mimetic activities. The present findings have important implications for the understanding of estrogen-dependent metabolic alterations with regards to situations of loss of estrogens as observed after menopause.

Hepatotoxicity of food-borne mycotoxins: molecular mechanism, anti-hepatotoxic medicines and target prediction

Mycotoxins are metabolites produced by fungi. The widespread contamination of food and feed by mycotoxins is a global food safety problem and a serious threat to people's health. Most food-borne mycotoxins have strong hepatotoxicity. However, no effective methods have been found to prevent or treat Mycotoxin- Induced Liver Injury (MILI) in clinical and animal husbandry. In this paper, the molecular mechanisms and potential anti-MILI medicines of six food-borne MILI are reviewed, and their targets are predicted by network toxicology, which provides a theoretical basis for further study of the toxicity mechanism of MILI and the development of effective strategies to manage MILI-related health problems in the future and accelerate the development of food safety.

Influence of Bisphenol Compounds at Nanomolar Concentrations on Chromosome Damage Induced by Metabolically Activated Carcinogens in HepG2 Cells

Bisphenol (BP) compounds are endocrine-disrupting organic pollutants. BPs may increase the messenger RNA (mRNA) transcripts of nuclear receptors (NRs) regulating the expression of xenobiotic-metabolizing cytochrome P450 (CYP) enzymes. Their impact on the genotoxicity of metabolically activated carcinogens, however, remains unknown. In this study, effects of the bisphenols A, F, S, and AF on the expression of the aryl hydrocarbon receptor (AhR), the pregnane X receptor (PXR), the constitutive androstane receptor, and individual xenobiotic-metabolizing CYP enzymes in a human hepatoma (HepG2) cell line were investigated, along with in silico binding studies of BPs to each receptor. The results indicated that each BP at 1 to 100 nM concentrations increased the mRNA transcripts and protein levels of AhR, PXR, CYP1A1, 1A2, 1B1, 2E1, and 3A4. The predicted affinities of the BPs for binding AhR were comparable to those of potent agonists. Pretreatment of HepG2 cells with each BP potentiated the induction of micronuclei by benzo[a]pyrene, aflatoxin B1, benzene, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; this effect was abolished/reduced by inhibitors of NRs and/or CYPs. Our study suggests that BPs at human exposure levels may aggravate chromosome damage by several impactful carcinogens in human cells by inducing relevant CYP enzymes, mostly via NR modulation.

Aflatoxins: History, Significant Milestones, Recent Data on Their Toxicity and Ways to Mitigation

In the early 1960s the discovery of aflatoxins began when a total of 100,000 turkey poults died by hitherto unknown turkey "X" disease in England. The disease was associated with Brazilian groundnut meal affected by Aspergillus flavus. The toxin was named Aspergillus flavus toxin-aflatoxin. From the point of view of agriculture, aflatoxins show the utmost importance. Until now, a total of 20 aflatoxins have been described, with B1, B2, G1, and G2 aflatoxins being the most significant. Contamination by aflatoxins is a global health problem. Aflatoxins pose acutely toxic, teratogenic, immunosuppressive, carcinogenic, and teratogenic effects. Besides food insecurity and human health, aflatoxins affect humanity at different levels, such as social, economical, and political. Great emphasis is placed on aflatoxin mitigation using biocontrol methods. Thus, this review is focused on aflatoxins in terms of historical development, the principal milestones of aflatoxin research, and recent data on their toxicity and different ways of mitigation.

Fucoidan supplementation modulates hepato-renal oxidative stress and DNA damage induced by aflatoxin B1 intoxication in rats

Aflatoxins are a common food contaminant of global concern. Aflatoxin B₁ (AFB₁) intoxication is associated with serious health hazards. Recently, fucoidan (FUC) has gained much attention from pharmaceutical industry due to its promising therapeutic effects. The impacts of FUC on AFB₁-induced liver and kidney injures have not been sufficiently addressed. This research was conducted to evaluate the ameliorative effect of FUC in AFB1-induced hepatorenal toxicity model in rats over 14 days. Five groups were assigned; control, FUC (200 mg/kg/day, orally), AFB₁ (50 μg/kg, i.p.), and AFB₁ plus a low or high dose of FUC. AFB₁ induced marked hepatorenal injury elucidated by substantial alterations in biochemical tests and histological pictures. The oxidative distress instigated by AFB₁ enhanced production of malondialdehyde (MDA) and nitric oxide (NO) along with reduction in the reduced-glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT) activities. DNA damage in the liver and kidney tissues has been demonstrated by overexpression of proliferating cell nuclear antigen (PCNA). Unambiguously, FUC consumption alleviates the AFB₁-induced mitochondrial dysfunction, oxidative harm, and apoptosis. These ameliorated effects are proposed to be attributed to fucoidan's antioxidant and anti-apoptotic activities. Our results recommend FUC supplementation to food because it exerts both preventive and therapeutic effects against AFB₁-induced toxicity.

Associations of persistent organic pollutants in human adipose tissue with retinoid levels and their relevance to the redox microenvironment

Humans are exposed to a myriad of chemical substances in both occupational and environmental settings. Persistent organic pollutants (POPs) have drawn attention for their adverse effects including cancer and endocrine disruption. Herein, the objectives were 1) to describe serum and adipose tissue retinol levels, along with serum retinol binding protein 4 (RBP4) concentrations, and 2) to assess the associations of adipose tissue POP levels with these retinoid parameters, as well as their potential interaction with the previously-observed POP-related disruption of redox microenvironment. Retinol was measured in both serum and adipose tissue along with RBP4 levels in serum samples of 236 participants of the GraMo adult cohort. Associations were explored by multivariable linear regression analyses and Weighted Quantile Sum regression. Polychlorinated biphenyls (PCBs) 180, 153 and 138 were related to decreased adipose tissue retinol levels and increased serum RBP4/retinol ratio. Dicofol concentrations > limit of detection were associated with decreased retinol levels in serum and adipose tissue. Additionally, increased adipose tissue retinol levels were linked to an attenuation in previously-reported associations of adipose tissue PCB-153 with in situ superoxide dismutase activity. Our results revealed a suggestive link between retinoids, PCBs and redox microenvironment, potentially relevant for both mechanistic and public health purposes.

Cytochrome P450-mediated mycotoxin metabolism by plant-feeding insects

Mycotoxins are secondary metabolites produced primarily by filamentous fungi that when consumed cause pathological responses in animal hosts or consumers. Defined functionally rather than structurally, mycotoxins derive from numerous primary metabolic pathways. Through opportunistic or mutualistic associations, insect herbivores inflict damage that can predispose plants to infection by mycotoxin-producing phytopathogens, resulting in economically significant contamination. The few cytochrome P450 subfamilies implicated in mycotoxin detoxification by insects, including CYP6 and CYP9, are also known to detoxify phytochemicals. Some insect P450s bioactivate, rather than detoxify, mycotoxins, suggestive of an 'escalation' in arms-race interactions between these herbivores and fungi. Characterizing insect P450s that detoxify mycotoxins can be useful for developing biological remediation technologies and for ensuring the safety of insects reared for human or livestock consumption.

Curcumin protects against Aflatoxin B1-induced liver injury in broilers via the modulation of long non-coding RNA expression

Aflatoxin B1 (AFB1) is a potent hepatotoxic and carcinogenic agent. Curcumin possesses potential anti-inflammatory, anti-oxidative and hepatoprotective effects. However, the role of LncRNAs in the protective mechanisms of curcumin against AFB1-induced liver damage is still elusive. Experimental broilers were randomly divided into 1) control group, 2) AFB1 group (1 mg/kg feed), 3) cur + AFB1 group (1 mg/kg AFB1 plus 300 mg/kg curcumin diet) and 4) curcumin group (300 mg/kg curcumin diet). Liver transcriptome analyses and qPCR were performed to identify shifts in genes expression. In addition, histopathological assessment and oxidant status were determined. Dietary AFB1 caused hepatic morphological injury, significantly increased the production of ROS, decreased liver antioxidant enzymes activities and induced inflammation and apoptosis. However, dietary curcumin partially attenuated the abnormal morphological changes, oxidative stress, and apoptosis in liver tissues. Transcriptional profiling results showed that 34 LncRNAs and 717 mRNAs were differentially expressed with AFB1 and curcumin co-treatment in livers of broilers. Analysis of the LncRNA-mRNA network, GO and KEGG enrichment data suggested that oxidative stress, inflammation and apoptosis pathway were crucial in curcumin's alleviating AFB1-induced liver damage. In conclusion, curcumin prevented AFB1-induced oxidative stress, inflammation and apoptosis through LncRNAs. These results provide new insights for unveiling the protective mechanisms of curcumin against AFB1-induced liver damage.

Exposure to pollutants altered glucocorticoid signaling and clock gene expression in female mice. Evidence of tissue- and sex-specificity

Environmental pollutants suspected of disrupting the endocrine system are considered etiologic factors in the epidemic of metabolic disorders. As regulation of energy metabolism relies on the integrated action of a large number of hormones, we hypothesized that certain chemicals could trigger changes in glucocorticoid signaling. To this end, we exposed C57Bl6/J female and male mice between 5 and 20 weeks of age to a mixture of 2,3,7,8- tetrachlorodibenzo-p-dioxin (20 pg/kg body weight/day [bw/d]), polychlorobiphenyl 153 (200 ng/kg bw/d), di-[2-ethylhexyl]-phthalate (500 μg/kg bw/d) and bisphenol A (40 μg/kg bw/d). In female mice fed a standard diet (ST), we observed a decrease in plasma levels of leptin as well as a reduced expression of corticoid receptors Nr3c1 and Nr3c2, of leptin and of various canonical genes related to the circadian clock machinery in visceral (VAT) but not subcutaneous (SAT) adipose tissue. However, Nr3c1 and Nr3c2 mRNA levels did not change in high-fat-fed females exposed to pollutants. In ST-fed males, pollutants caused the same decrease of Nr3c1 mRNA levels in VAT observed in ST-fed females but levels of Nr3c2 and other clock-related genes found to be down-regulated in female VAT were enhanced in male SAT and not affected in male VAT. The expression of corticoid receptors was not affected in the livers of both sexes in response to pollutants. In summary, exposure to a mixture of pollutants at doses lower than the no-observed adverse effect levels (NoAELs) resulted in sex-dependent glucocorticoid signaling disturbances and clock-related gene expression modifications in the adipose tissue of ST-fed mice.

Metabolism-Disrupting Chemicals and the Constitutive Androstane Receptor CAR

During the last two decades, the constitutive androstane receptor (CAR; NR1I3) has emerged as a master activator of drug- and xenobiotic-metabolizing enzymes and transporters that govern the clearance of both exogenous and endogenous small molecules. Recent studies indicate that CAR participates, together with other nuclear receptors (NRs) and transcription factors, in regulation of hepatic glucose and lipid metabolism, hepatocyte communication, proliferation and toxicity, and liver tumor development in rodents. Endocrine-disrupting chemicals (EDCs) constitute a wide range of persistent organic compounds that have been associated with aberrations of hormone-dependent physiological processes. Their adverse health effects include metabolic alterations such as diabetes, obesity, and fatty liver disease in animal models and humans exposed to EDCs. As numerous xenobiotics can activate CAR, its role in EDC-elicited adverse metabolic effects has gained much interest. Here, we review the key features and mechanisms of CAR as a xenobiotic-sensing receptor, species differences and selectivity of CAR ligands, contribution of CAR to regulation hepatic metabolism, and evidence for CAR-dependent EDC action therein.

Influence of polychlorinated biphenyls and organochlorine pesticides on the inflammatory milieu. A systematic review of in vitro, in vivo and epidemiological studies

BACKGROUND

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are relevant families of persistent organic pollutants, which have been linked to several long-term adverse health effects. The mechanisms of action of these pollutants are still poorly understood. However, there are some evidences suggesting that inflammation might play a key role on their effects.

AIM

To systematically synthesize the published in vitro, in vivo and epidemiological data assessing the potential influence of exposure to OCPs and PCBs on the development of an inflammatory milieu.

METHODS

A systematic review of peer-reviewed original research papers published until 1st May 2019 was conducted, by using Medline, Web of Science and Scopus databases. A total of 39 articles met the inclusion criteria and were evaluated in this review.

RESULTS

The majority of the studies showed significant associations of PCB and OCP exposure with all inflammatory markers measured (n = 30). Some studies showed positive and negative associations (n = 7) and only two studies evidenced negative associations (n = 2). Most of the available evidences came from in vitro and in vivo studies (n = 31), with few epidemiological studies (n = 8).

CONCLUSIONS

We found consistent positive associations between exposure to PCBs and OCPs and the development of a pro-inflammatory milieu, with only few discrepancies. However, given the limited epidemiological evidence found, our results warrant further research in order to elucidate the real contribution of these pollutants on the inflammatory processes and subsequent diseases.

Insights into Aflatoxin B1 Toxicity in Cattle: An In Vitro Whole-Transcriptomic Approach

Aflatoxins, and particularly aflatoxin B1 (AFB1), are toxic mycotoxins to humans and farm animal species, resulting in acute and chronic toxicities. At present, AFB1 is still considered a global concern with negative impacts on health, the economy, and social life. In farm animals, exposure to AFB1-contaminated feed may cause several untoward effects, liver damage being one of the most devastating ones. In the present study, we assessed in vitro the transcriptional changes caused by AFB1 in a bovine fetal hepatocyte-derived cell line (BFH12). To boost the cellular response to AFB1, cells were pre-treated with the co-planar PCB 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), a known aryl hydrocarbon receptor agonist. Three experimental groups were considered: cells exposed to the vehicle only, to PCB126, and to PCB126 and AFB1. A total of nine RNA-seq libraries (three replicates/group) were constructed and sequenced. The differential expression analysis showed that PCB126 induced only small transcriptional changes. On the contrary, AFB1 deeply affected the cell transcriptome, the majority of significant genes being associated with cancer, cellular damage and apoptosis, inflammation, bioactivation, and detoxification pathways. Investigating mRNA perturbations induced by AFB1 in cattle BFH12 cells will help us to better understand AFB1 toxicodynamics in this susceptible and economically important food-producing species.

Polychlorinated biphenyl quinone induces hepatocytes iron overload through up-regulating hepcidin expression

Polychlorinated biphenyls (PCBs) are infamous industry by-products or additives, and increasing evidences demonstrated that their exposure is associate with adverse effects on human health. Liver, as the dominate site for xenobiotic metabolism, is apt to be the primary target of PCBs insult. Although PCBs' hepatic toxic effects have been extensively studied, however, the biotransformation of PCBs in liver and the toxicities of associated PCB metabolites are neglected at some extent. Thus, we choose 2,3,5-trichloro-6-phenyl-[1,4]-benzoquinone (PCB29-pQ), a surrogate PCB29 metabolite, and evaluated its contribution on hepatotoxicity. In the current study, we discovered PCB29-pQ-induced lipid peroxidation and iron overload both in vivo and in vitro. Further mechanistic research confirmed iron overload is caused by reactive oxygen species (ROS)-driven hepcidin disorder in hepatic cells, and the increase of hepcidin is regulated by the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2).

Alterations in viability and CYP1A1 expression in SH SY5Y cell line by pollutants present in Madín Dam, Mexico

Currently one of the problems facing global development is the availability of water. Although water is abundant the planet only a small portion is for human use and consumption. The problem is exacerbated due to different factors, mainly: meteorological phenomena, the presence of contaminants in the water and the increase in the number of inhabitants. Potential effects of pollutants not only can affect freshwater biota but also can be implicated in cancer development and neurodegenerative diseases in humans. The study was conducted in the Madín Dam, a reservoir of economic importance for the geographical area in which it is located, as well as catering to the population of nearby areas, and is a place where recreational activities such as fishing and kayaking are carried out. The aim of this study was to identify the toxic effects that the pollutants present in the water of the Madín Dam can generate on a human cell line (SH SY5Y) evaluating the cell viability and the participation of the Aril Hydrocarbon Receptor (AhR) and Pregnane X receptor (PXR) through of the expression of the CYP1A1 and CYP3A4 (canonical genes). In one of the five sites analyzed, cell viability was up to 50%, in this site a decrease in the normal expression of CYP1A1 was observed (p < 0.05) and the CYP3A4 gene was not expressed in the cells SH SY5Y. These results show that the SH SY5Y cell line is a good biomarker for assessing the human toxicity of environmental pollutants and relating it to neurodegenerative diseases.

CYP2A13 Acts as the Main Metabolic CYP450s Enzyme for Activating Leonurine in Human Bronchial Epithelial Cells

Background

Leonurine is an active component of the traditional Chinese medicine Leonurus japonicus. This study aimed to investigate the effects of overexpressed CYP450s on the metabolic activity of leonurine.

Material/Methods

BEAS-2B cells stably expressing CYP1A1, 1A2, 2A13, 2B6, and 3A4 were constructed. CYP450s expression was identified using reverse-transcription PCR and Western blot assay. CCK-8 assay was used to evaluate the effect of leonurine on cell activity. Leonurine was incubated in vitro with CYP1A1, 1A2, 2A13, 2B6, and 3A4 metabolic enzymes to evaluate the clearance rate of CYP450 enzymes for leonurine. UPLC-MS was used to detect changes of drug concentration and discover the main metabolic enzymes affecting leonurine.

Results

BEAS-2B cells stably expressing CYP1A1, 1A2, 2A13, 2B6, and 3A4 were successfully constructed. According to primary mass spectra and secondary mass spectra of leonurine, the main metabolic enzymes were 312.1550 [H+] and 181.0484. Compared to the control group, residue of leonurine in CYP2A13 group was significantly reduced (F=5.307, p=0.024). Compared to the 0-min group, the clearance rate of leonurine in the CYP2A13-treated group was significantly decreased at 120 min after treatment (F=7.273, p=0.007). CCK-8 results also showed that activity of BEAS-2B cells that overexpress CYP2A13 gradually decreased with increased concentration of leonurine. Although CYP2A13 demonstrated good metabolic activity for leonurine, we found that CYP1A1, 1A2, 2B6, and 3A4 had no metabolic effects on leonurine.

Conclusions

Leonurine can be effectively activated through CYP2A13 enzyme metabolism, and further inhibits activity of human lung epithelial cells (BEAS-2B). Therefore, CYP2A13 is a main metabolic enzyme for leonurine in BEAS-2B cells.

Micronuclei Formation by Promutagens in Metabolism-Incompetent V79 Cells Interacting With Activation-Proficient Cells in Various Experimental Settings

The accessibility of reactive metabolites to test cells is critical for a genotoxic response. However, sulfo-conjugates formed outside may not readily enter cells, and some metabolites formed by cytochromes P450 (CYPs) may not endure transport. This topic was addressed in the present study, using V79 cells engineered for human CYPs and/or a sulfotransferase (SULT). First, 1-methylpyrene, 1-hydroxymethylpyrene, benzo[a]pyrene, and aflatoxin B1 significantly induced micronuclei in V79-hCYP1A2-hSULT1A1, V79-hSULT1A1, V79-hCYP1A1, and V79-hCYP1A2 cells, respectively. Subsequently, we used these cell lines as external activating systems in various experimental settings in combination with V79-derived target cells lacking critical enzymes. 1-Methylpyrene (activated by CYPs and SULTs sequentially) showed an activity similar to that in V79-hCYP1A2-hSULT1A1 cells, in each following model: a mixed V79-hCYP1A2:V79-hSULT1A1 (1:1) culture, exposure of V79-hCYP1A2 to 1-methylpyrene followed by transfer of medium to V79-hSULT1A1 target cells, and V79-hSULT1A1 communicating with V79-hCYP1A2 through 0.4-μm pores and over a 1-mm distance in a unique transwell system. These results suggest ready transfer of 1-hydroxymethylpyrene formed in V79-hCYP1A2 to V79-hSULT1A1 for further activation. In the last two models, with V79-hSULT1A1 for activation and V79-Mz as target, 1-hydroxymethylpyrene induced micronuclei mildly, suggesting limited intercellular transfer of the ultimate genotoxicant, 1-sulfooxymethylpyrene. Benzo[a]pyrene induced micronuclei in V79-Mz communicating with V79-hCYP1A1 via porous membranes, whereas aflatoxin B1 was inactive in V79-Mz communicating with V79-hCYP1A2. Our results suggest that the sulfo-conjugate tested may have difficulty entering cells for a genotoxic effect, and the reactive metabolite of aflatoxin B1, unlike that of benzo[a]pyrene, could not travel an adequate distance to enter cells. Environ. Mol. Mutagen. 61:224-234, 2020. © 2019 Wiley Periodicals, Inc.

Dioxin-like (DL-) polychlorinated biphenyls induced immunotoxicity through apoptosis in mice splenocytes via the AhR mediated mitochondria dependent signaling pathways

Polychlorinated biphenyls (PCBs) would do serious damage to multiple systems, while coplanar polychlorinated biphenyls, the most toxic member of the family, has been widely taken into consideration. In this study, ICR mice were fed with different doses of PCB126 to explore the underlying molecular mechanisms on immunotoxicity. The results showed that PCB126 caused immunosuppression as evidenced by inhibiting the ratios of thymus and spleen weights, changing the organizational structure and decreasing levels and mRNA expression of TNF-α, IFN-γ and IL-2. PCB126 inhibited the SOD activity and spurred the accumulation of MDA in spleen and thymus. Meanwhile, it also disturbed the Nrf2 signaling pathway as evidenced by up-regulating the mRNA expression of Nrf2 and Keap1. Additionally, a remarkable reduction in the mRNA expression of AhR and enhancement in the mRNA expression of Cyp1 enzymes (Cyp1a1, Cyp1a2 and Cyp1b1) were observed, which increased the ROS levels. PCB126 could increase protein expression of Bax, Caspase-3, Caspase-8 and Caspase-9, while the protein expression of Bcl-2 was decreased. In summary, the results indicated that PCB126 modulated the AhR signaling pathway, which interacted with apoptosis and oxidative stress to induce immunotoxicity, enrich the immunotoxicological mechanisms of PCB126.

To freeze, or not to freeze: the impact of subzero temperature on quantifying organic contaminants in ocean sediments

Assessing the extent of ocean bed contamination by anthropogenic organic chemicals requires collecting and preserving the native state of sediments. The latter is particularly important since most sediment analyses are performed away from the sites of samples collection. Preservation, however, is presumptuous since commonly used sediment handling practices such as freezing are structurally disruptive, the impacts of which are not well understood. In this study, the impact of freezing on quantifying the total organic carbon (TOC) contents and the extent of PAH, DDT and PCB contamination in 17 split-paired sediment samples was investigated. The samples were collected from the Santa Monica Bay, California (USA). One-half of each split-pair was frozen at -20 °C and the other half was refrigerated at 4 °C for up to 11 days. The results suggest that no significant differences exist between the frozen and the refrigerated datasets for PCBs (F1,28 = 4.01, p > 0.05), DDTs (n = 16, t-Stat < t-Critical, p > 0.05) or TOC (n = 16, t-Stat < t-Critical, p > 0.05). The results however show that less PAHs were detected in the frozen sediments (F1,24 = 8.18, p < 0.05) than in the refrigerated sediments; the larger PAHs were affected the most. Interestingly, while benzo[a]pyrene, a large PAH molecule, was affected by this apparent temperature-induced difference, its structural isomer, benzo[e]pyrene, was not. Even more interesting was the finding that while non-coplanar PCBs were affected similarly, the coplanar PCBs were not. Overall, sediment freezing within this study's timeframe appears to offer little contextual advantage over sediment refrigeration.