Fluoranthene enhances p53 expression and decreases mutagenesis induced by benzo[a]pyrene

Dexlansoprazole is an aryl hydrocarbon receptor agonist

Dexlansoprazole, a proton pump inhibitor, is commonly used to treat gastro-esophageal reflux disease and erosive esophagitis. The activated aryl hydrocarbon receptor (AhR) functions as a transcription factor by binding to the aryl hydrocarbon response element (AHRE) of its target genes, with cytochrome P450 (CYP) 1A1 being the most well-known target. In this study, we demonstrated that dexlansoprazole stimulates AhR activity, leading to increased CYP1A1 expression. Our findings indicate that treatment with 2 μM dexlansoprazole is sufficient to induce CYP1A1 mRNA and protein expression, as well as AHRE-mediated transcriptional activity, in both human and mouse cells. Using AhR signal-deficient mutant cells and specific AhR antagonists-SR1, GNF351, and CH-223191-we confirmed that AhR is required for dexlansoprazole-induced CYP1A1 expression. Additionally, we showed that dexlansoprazole promotes AhR nuclear translocation, acting as an AhR agonist. However, due to its lower potency compared to FICZ and ITE in activating AhR, dexlansoprazole suppresses FICZ- and ITE-induced CYP1A1 expression in human liver HepG2 and ovarian granulosa HO23 cell lines, suggesting that it functions as both an AhR agonist and a modulator. This study offers valuable insights into the potential clinical side effects of dexlansoprazole.

Proteomic Analysis of the Protective Effect of Eriodictyol on Benzo(a)pyrene-Induced Caco-2 Cytotoxicity

We evaluated the possible protective effects of six polyphenols on benzo(a)pyrene (BaP)-induced cytotoxicity in Caco-2 cells. We show that treatment with quinic acid, ferulic acid, homovanillic acid, trolox and BaP decreased cell viability, whereas naringenin and eriodictyol affected viability in a bi-phasic manner with low concentrations decreasing viability whereas higher concentrations increase viability. Co-treatment with 20 μM eriodictyol or naringenin reduced BaP-induced cytotoxicity, including cell apoptosis, cell cycle progression, and oxidative stress. Our results show that the protective effect of eriodictyol was superior to that of naringenin. The potential protective mechanisms of eriodictyol on BaP-induced toxicity were investigated by proteomics. We identified 80 differentially expressed proteins (DEPs) with proteins associated with genetic information processing pathway representing the highest proportion and number of proteins responding to eriodictyol treatment, including key proteins such as RPA2, SNRPA, RAD23B, NUP155 and AARS. Our results provide new knowledge on how polyphenols may prevent BaP-induced carcinogenesis.

Cyproterone acetate acts as a disruptor of the aryl hydrocarbon receptor

Prostate cancer is a major cause of death in males. Cyproterone acetate (CPA), the steroidal anti-androgen for part of androgen deprivation therapy, may block the androgen-receptor interaction and then reduce serum testosterone through its weak anti-gonadotropic action. In addition to CPA inducing hepatitis, CPA is known to cause liver tumors in rats also. Aryl hydrocarbon receptor (AhR) is a cytoplasmic receptor and regulates multiple physiological functions. CYP1A1 is an AhR-targeted gene. We found that CPA induced CYP1A1 expression, transcriptional activity of the aryl hydrocarbon response element (AHRE), and the nuclear localization of AhR in mouse Hepa-1c1c7 cells. However, CPA suppressed CYP1A1 mRNA expression and the transcriptional activity of AHRE in human HepG2 and MCF7 cells, and also decreased AhR ligand-induced CYP1A1 protein expression and transcriptional activity of AHRE in HepG2 cells. In summary, CPA is an AhR agonist in mouse cells, but an AhR antagonist in human cells. Accordingly, CPA potentially plays a role as an endocrine disruptor of the AhR. This study helps us to understand why CPA induces acute hepatitis, gene mutation, and many other side effects. In addition, it may trigger further studies investigating the relationships between CPA, glucocorticoid receptor and castration-resistant prostate cancer in the future.

Impact of Mixture Effects between Emerging Organic Contaminants on Cytotoxicity: A Systems Biological Understanding of Synergism between Tris(1,3-dichloro-2-propyl)phosphate and Triphenyl Phosphate

Humans are exposed to many xenobiotics simultaneously, but little is known about the toxic effects based on chemical-chemical interactions. This study aims at evaluating the binary interactions between 13 common environmental organic compounds (resulting in 78 pairs) by observing their cytotoxicity on HepG2 cells. Among all of the tested pairs, the combination of flame-retardant triphenyl phosphate (TPP) and tris(1,3-dichloro-2-propyl)phosphate (TDCPP) exhibited one of the most significant synergistic effects. We further characterized the transcriptome and metabolome after combined exposure to TPP and TDCPP and individual exposure. The results suggested that the coexposure caused many more changes in gene expressions and cellular activities. The transcriptome data showed that the coexposure triggered significant pathway changes including "cholesterol biosynthesis" and "ATF6-Alpha activated chaperone genes", together with distinct gene ontology (GO) terms such as the "negative regulation of the ERK1 and ERK2 cascade". Additionally, coexposure enhanced the biological activity of liver X receptors and nuclear factor erythroid 2-related factor 2 (Nrf2). The metabolome data showed that coexposure significantly elevated oxidative stress and affected the purine and pyrimidine metabolism. Overall, this study showed that interactions, which may enhance or suppress the biological processes, are common among environmental chemicals, although their environmental relevance should be studied in the future.

Benzo(a)pyrene-induced a mitochondria-independent apoptosis of liver in juvenile Chinese rare minnows (Gobiocypris rarus)

To examine the effects of BaP on tissue apoptosis, laboratory studies were conducted using juvenile Chinese rare minnows (Gobiocypris rarus) exposed to 1, 5, 20, and 80 μg/L of BaP for 28 days. The post-treatment pathological findings in the liver were associated with hepatocyte swelling, karyopyknosis, and karyorrhexis. Moreover, an increase in the goblet cells in the intestine, epithelial hyperplasia of the gills and fusion of gill lamellae were observed. Significant increases in hepatocyte apoptosis using the TUNEL stain were observed in the liver tissue but not in the intestine and gills. In addition, BaP exposure significantly up-regulated the mRNA levels of cyp1a1, p53, bax, bcl-2, and caspase-9 in the liver following the 5, 20, and 80 μg/L treatments, whereas the apaf-1 was significantly down-regulated following all treatments. Moreover, the activities of caspase 3 and caspase 8 were markedly elevated, whereas the protein expression levels of Apaf-1 were down-regulated following the 20 and 80 μg/L treatments. Taken together, our results suggested that BaP strongly induces tissue-specific apoptosis in vivo, leading to significant pathological changes. The responsiveness of apoptotic-related genes demonstrates that BaP induced apoptosis in the liver may be through a mitochondria-independent pathway.

Benzo[a]pyrene Induces Autophagic and Pyroptotic Death Simultaneously in HL-7702 Human Normal Liver Cells

As a common polycyclic aromatic hydrocarbon compound, benzo[a]pyrene (BaP) is readily produced in processing of oil and fatty foods. It is not only a strong carcinogen but also a substance with strong immunotoxicity and reproduction toxicity. Autophagy and pyroptosis are two types of programmed cell death. Whether or not BaP damages body tissues via autophagy or pyroptosis remains unknown. The present study investigated the effects of BaP on autophagy and pyroptosis in HL-7702 cells. The results showed that BaP induced cell death in HL-7702 cells enhanced the intracellular levels of ROS and arrested the cell cycle at the S phase. Additionally, BaP resulted in cell death through autophagy and pyroptosis. Compared with the BaP group, the autophagy inhibitor 3-MA significantly (p < 0.01) inhibited the release of LDH by 70.53% ± 0.46 and NO by 50.36% ± 0.80, the increase of electrical conductivity by 12.08% ± 0.55, and the expressions of pyroptotic marker proteins (Caspase-1, Cox-2, IL-1β, IL-18). The pyroptosis inhibitor Ac-YVAD-CM also notably (p < 0.01) blocked BaP-induced autophagic cell death characterized by the increase of autophagic vacuoles and overexpression of Beclin-1 and LC3-II. In conclusion, BaP led to injury by inducing autophagy and pyroptosis simultaneously, the two of which coexisted and promoted each other in HL-7702 cells.

Characteristics, sources, and cytotoxicity of atmospheric polycyclic aromatic hydrocarbons in urban roadside areas of Hangzhou, China

The primary objective of this study is to understand the profiles, sources and cytotoxic effects of atmospheric polycyclic aromatic hydrocarbons (PAHs), which are closely related to urban air contamination and public health, in urban roadside environments. On-road sampling campaigns were conducted from 2014 to 2015 at three urban road sites in Hangzhou, China. Sixteen gaseous and particulate matter (PM) 2.5-bound PAHs were identified and quantified using gas chromatography-mass spectrometry (GC-MS). The total PAH concentrations at the three sites ranged from 750 to1142 ng/m³ and 1050 to 1483 ng/m³ in summer and winter, respectively. Low molecular weight PAHs were the most abundant compounds (77-86%) and primarily existed in gas phase. The concentrations and phase distributions of high molecular weight PAHs were varied at three sites due to the differences in traffic volume, vehicle composition, engine loading, and nearby artificial activity. Diagnostic ratios of the principal mass (m/z,178, 202, 228 and 276) parent PAHs were statistically described to determine the PAH sources to urban roadsides; principal component analysis (PCA) was applied to apportion the sources. The results indicated that high- and low-temperature fuel processes, as well as residential and industrial emissions, were major contributors to roadside PAHs. The cytotoxic potential of the roadside PAHs was evaluated using a human epithelial lung cell line (A549). Cell viability was measured after a direct exposure to PAH extract. The results reflected the profiles of roadside PAHs at the three sites. The cytotoxicity of reference PAHs was evaluated to provide further insights into the cytotoxic potential of PAHs. We found that low molecular weight PAHs, which are less cytotoxic compounds, synergistically promoted the lethal effect of cytotoxic compounds, posing a potential threat to public health.

Synergistic and antagonistic interactions of binary mixtures of polycyclic aromatic hydrocarbons in the upregulation of CYP1 activity and mRNA levels in precision-cut rat liver slices

The current studies investigate whether synergistic or antagonistic interactions in the upregulation of CYP1 activity occur in binary mixtures of polycyclic aromatic hydrocarbons (PAHs) involving benzo[a]pyrene and five other structurally diverse PAHs of varying carcinogenic activity. Precision-cut rat liver slices were incubated with benzo[a]pyrene alone or in combination with a range of concentrations of a second PAH, and ethoxyresorufin O-deethylase, CYP1A1 and CYP1B1 mRNA levels determined. Concurrent incubation of benzo[a]pyrene with either dibenzo[a,h]anthracene or fluoranthene in liver slices led to a synergistic interaction, at least at low concentrations, in that ethoxyresorufin O-deethylase activity was statistically higher than the added effects when the slices were incubated with the individual compounds. In contrast, benzo[b]fluoranthene and, at high doses only, dibenzo[a,l]pyrene gave rise to antagonism, whereas 1-methylphenanthrene had no effect at all concentrations studied. When CYP1A1 mRNA levels were monitored, benzo[b]fluoranthene gave rise to an antagonistic response when incubated with benzo[a]pyrene, whereas all other compounds displayed synergism, with 1-methylphenathrene being the least effective. A similar picture emerged when CYP1B1 mRNA levels were determined, though the effects were less pronounced. In conclusion, it has been demonstrated that the benzo[a]pyrene-mediated upregulation of CYP1, at the mRNA and activity levels, is synergistically and antagonistically modulated by other PAHs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 764-775, 2017.

Inhibition of the formation of benzo[a]pyrene adducts to DNA in A549 lung cells exposed to mixtures of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants, which exhibit carcinogenic properties especially in lungs. In the present work, we studied the effect of mixtures of 12 PAHs on the A549 alveolar cells. We first assess the ability of each PAH at inducing gene expression of phase I metabolization enzymes and at generating DNA adducts. A good correlation was found between these two endpoints. We then exposed cells to either binary mixtures of the highly genotoxic benzo[a]pyrene (B[a]P) with each PAH or complex mixtures of all studied PAHs mimicking by real emissions including combustion of wood, cigarette smoke, and atmospheres of garage, silicon factory and urban environments. Compared to pure B[a]P, both types of mixtures led to reduced CYP450 activity measured by the EROD test. A similar trend was observed for the formation of DNA adducts. Surprisingly, the complex mixtures were more potent than B[a]P used at the same concentration for the induction of genes coding for CYP. Our results stress the lack of additivity of the genotoxic properties of PAH in mixtures. Interestingly, an opposite synergy in the formation of B[a]P adducts were observed previously in hepatocytes. Our data also show that measurement of the metabolic activity rather than quantification of gene expression reflects the actual bioactivation of PAHs into DNA damaging species.

Biological impact of environmental polycyclic aromatic hydrocarbons (ePAHs) as endocrine disruptors

Polycyclic aromatic hydrocarbons (PAHs) are often detected in the environment and are regarded as endocrine disruptors. We here designated mixtures of PAHs in the environment as environmental PAHs (ePAHs) to discuss their effects collectively, which could be different from the sum of the constituent PAHs. We first summarized the biological impact of environmental PAHs (ePAHs) found in the atmosphere, sediments, soils, and water as a result of human activities, accidents, or natural phenomena. ePAHs are characterized by their sources and forms, followed by their biological effects and social impact, and bioassays that are used to investigate their biological effects. The findings of the bioassays have demonstrated that ePAHs have the ability to affect the endocrine systems of humans and animals. The pathways that mediate cell signaling for the endocrine disruptions induced by ePAHs and PAHs have also been summarized in order to obtain a clearer understanding of the mechanisms responsible for these effects without animal tests; they include specific signaling pathways (MAPK and other signaling pathways), regulatory mechanisms (chromatin/epigenetic regulation, cell cycle/DNA damage control, and cytoskeletal/adhesion regulation), and cell functions (apoptosis, autophagy, immune responses/inflammation, neurological responses, and development/differentiation) induced by specific PAHs, such as benz[a]anthracene, benzo[a]pyrene, benz[l]aceanthrylene, cyclopenta[c,d]pyrene, 7,12-dimethylbenz[a]anthracene, fluoranthene, fluorene, 3-methylcholanthrene, perylene, phenanthrene, and pyrene as well as their derivatives. Estrogen signaling is one of the most studied pathways associated with the endocrine-disrupting activities of PAHs, and involves estrogen receptors and aryl hydrocarbon receptors. However, some of the actions of PAHs are contradictory, complex, and unexplainable. Although several possibilities have been suggested, such as direct interactions between PAHs and receptors and the suppression of their activities through other pathways, the mechanisms underlying the activities of PAHs remain unclear. Thus, standardized assay protocols for pathway-based assessments are considered to be important to overcome these issues.

Exposure of sea bream (Sparus aurata) to toxic concentrations of benzo[a]pyrene: possible human health effect

Polycyclic aromatic hydrocarbons (PAHs) can accumulate in the food chain, due to their lipophilic properties. Fish can accumulate contaminants including PAHs and frequent consumption of such contaminated fish can pose risk to human health. The aim of this study was to clarify if acute exposure of sea bream (Sparus aurata, a fish species of great economic importance in the Atlantic and Mediterranean areas) to a PAH, benzo[a]pyrene (B[a]P), at a dose that can induce CYP1A and pathological changes in fish gills, liver and muscle, can induce accumulation in muscle. We investigated the cytotoxic effects (as changes in cell viability, DNA laddering and glutathione content) of in vitro exposure of human peripheral blood mononuclear cells (PBMCs) to organic extracts obtained from muscle of sea breams previously exposed via water to B[a]P (2mg/l, for 12, 24 and 72 h). At this level of exposure, B[a]P caused morphological changes, inflammatory response and CYP1A induction not only in sea bream gills and liver but also in muscle; furthermore, in fish muscle we observed a substantial B[a]P accumulation, which may be associated with the increased CYP1A activity in liver and especially in muscle. However, when PBMCs were exposed to organic extracts obtained from sea bream muscle contaminated with B[a]P, a toxic, although modest effect was revealed, consisting in a significant decrease in cell glutathione levels without alterations in cell viability and DNA laddering. This suggests that consumption of sea breams from B[a]P contaminated waters might represent a risk for human health.

Tumour suppressor protein p53 regulates the stress activated bilirubin oxidase cytochrome P450 2A6

Human cytochrome P450 (CYP) 2A6 enzyme has been proposed to play a role in cellular defence against chemical-induced oxidative stress. The encoding gene is regulated by various stress activated transcription factors. This paper demonstrates that p53 is a novel transcriptional regulator of the gene. Sequence analysis of the CYP2A6 promoter revealed six putative p53 binding sites in a 3kb proximate promoter region. The site closest to transcription start site (TSS) is highly homologous with the p53 consensus sequence. Transfection with various stepwise deletions of CYP2A6-5'-Luc constructs--down to -160bp from the TSS--showed p53 responsiveness in p53 overexpressed C3A cells. However, a further deletion from -160 to -74bp, including the putative p53 binding site, totally abolished the p53 responsiveness. Electrophoretic mobility shift assay with a probe containing the putative binding site showed specific binding of p53. A point mutation at the binding site abolished both the binding and responsiveness of the recombinant gene to p53. Up-regulation of the endogenous p53 with benzo[α]pyrene--a well-known p53 activator--increased the expression of the p53 responsive positive control and the CYP2A6-5'-Luc construct containing the intact p53 binding site but not the mutated CYP2A6-5'-Luc construct. Finally, inducibility of the native CYP2A6 gene by benzo[α]pyrene was demonstrated by dose-dependent increases in CYP2A6 mRNA and protein levels along with increased p53 levels in the nucleus. Collectively, the results indicate that p53 protein is a regulator of the CYP2A6 gene in C3A cells and further support the putative cytoprotective role of CYP2A6.

AKT mediates actinomycin D-induced p53 expression

At high cytotoxic concentrations, actinomycin D (ActD) blocks transcription, decreasing levels of MDM2 and thus causing p53 stabilization. At low cytostatic concentrations, ActD causes ribosomal stress, which decreases MDM2 activity, resulting in p53 stabilization and activation. ActD can thus be used for p53-based cyclotherapy. We analyzed pathways mediating ActD-induced p53 expression. Inhibitors (LY294002, wortmannin, and deguelin) of phosphatidylinositol 3-kinases (PI3K) and AKT, but not inhibitors of MEK1/2, JNK, and p38-MAPK abolished the ActD-induced p53 expression in diverse cell types. RNA interference further supported these results. When AKT was downregulated by small hairpin RNA-AKTs, ActD-induced p53 expression was significantly decreased. ActD caused AKT phosphorylation at Ser473, indicating full activation of AKT. The potential for cancer therapy is discussed.

Polymorphisms of genes involved in polycyclic aromatic hydrocarbons' biotransformation and atherosclerosis

Polycyclic aromatic hydrocarbons (PAHs) are among the most prevalent environmental pollutants and result from the incomplete combustion of hydrocarbons (coal and gasoline, fossil fuel combustion, byproducts of industrial processing, natural emission, cigarette smoking, etc.). The first phase of xenobiotic biotransformation in the PAH metabolism includes activities of cytochrome P450 from the CYP1 family and microsomal epoxide hydrolase. The products of this biotransformation are reactive oxygen species that are transformed in the second phase through the formation of conjugates with glutathione, glucuronate or sulphates. PAH exposure may lead to PAH-DNA adduct formation or induce an inflammatory atherosclerotic plaque phenotype. Several genetic polymorphisms of genes encoded for enzymes involved in PAH biotransformation have been proven to lead to the development of diseases. Enzyme CYP P450 1A1, which is encoded by the CYP1A1 gene, is vital in the monooxygenation of lipofilic substrates, while GSTM1 and GSTT1 are the most abundant isophorms that conjugate and neutralize oxygen products. Some single nucleotide polymorphisms of the CYP1A1 gene as well as the deletion polymorphisms of GSTT1 and GSTM1 may alter the final specific cellular inflammatory respond. Occupational exposure or conditions from the living environment can contribute to the production of PAH metabolites with adverse effects on human health. The aim of this study was to obtain data on biotransformation and atherosclerosis, as well as data on the gene polymorphisms involved in biotransformation, in order to better study gene expression and further elucidate the interaction between genes and the environment.

Benzo(a)pyrene modulates fluoranthene-induced cellular responses in HT-29 colon cells in a dual exposure system

Our environment is contaminated with a diverse array of chemicals; one of which is polycyclic aromatic hydrocarbons (PAHs). While some PAHs are potent by nature, others undergo interactions such as additivity, synergism, antagonism or potentiation to manifest their toxicity. Therefore, the objective of this study was to investigate whether exposure to benzo(a)pyrene (BaP), a PAH compound influences the cytotoxicity and metabolism of fluoranthene (FLA; another PAH compound) using HT-29 cells. Cells cultured in Dulbecco's Modified Eagle Medium were treated with 1, 5, 10, 25μM BaP and FLA (0.01% dimethylsulfoxide as vehicle) individually and in combination over the course of 0-96h. At the end of exposure, cells were stained with propidium iodide and the changes in cell cycle were analyzed using FACS analysis. Apoptosis was determined by caspase-3 assay. Post-incubation, samples were extracted and analyzed for FLA metabolites by reverse-phase HPLC with fluorescence detection. Cells exposed to BaP+FLA showed a marginal decrease in growth as compared to FLA alone and vehicle controls. Also, a decline in the percentage of cells in the S and G2 phases compared to G1 phase of cell cycle was noted when cells were treated with BaP and FLA together, compared to individual FLA treatment. The rate of FLA metabolism was more when cells were exposed to FLA in combination with BaP, compared to FLA alone. The enhanced biotransformation of FLA as a result of concomitant exposure to BaP may have implications for colon cancer risks arising from human dietary exposure to PAH mixtures through consumption of barbecued meat.

Cyprodinil as an activator of aryl hydrocarbon receptor

Cyprodinil is a pyrimidinamine fungicide, used worldwide by agriculture. It is used to protect fruit plants and vegetables from a wide range of pathogens. Benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are toxic environmental pollutants and are prototypes of aryl hydrocarbon receptor (AHR) ligands. Although the structure of cyprodinil distinctly differs from those of BaP and TCDD, our results show that cyprodinil induced nuclear translocation of the AHR, and induced the transcriptional activity of aryl hydrocarbon response element (AHRE). Cyprodinil induced the expression of cytochrome P450 (CYP) 1A1, a well-known AHR-targeted gene, in ovarian granulosa cells, HO23, and hepatoma cells, Hepa-1c1c7. Its induction did not appear in AHR signal-deficient cells, and was blocked by the AHR antagonist, CH-223191. Cyprodinil decreased AHR expression in HO23 cells, resulting in CYP1A1 expression decreasing after it peaked at 9h of treatment in HO23 cells. Dexamethasone is a synthetic agonist of glucocorticoids. Cyprodinil enhanced dexamethasone-induced gene expression, and conversely, its induction of CYP1A1 expression was decreased by dexamethasone in HO23 cells, indicating its induction of crosstalk between the AHR and glucocorticoid receptor and its role as a potential endocrine disrupter. In addition to BaP, TCDD, and an AHR agonist, β-NF, cyprodinil also phosphorylated extracellular signal-regulated kinase (ERK) in HO23 and Hepa-1c1c7 cells, indicating its deregulation of ERK activity. In summary, our results demonstrate that cyprodinil, similar to BaP, acts as an AHR activator, a potential endocrine disrupter, and an ERK disrupter.