Latest Publications

@article{andrysik_activation_2011,

title = {Activation of the aryl hydrocarbon receptor is the major toxic mode of action of an organic extract of a reference urban dust particulate matter mixture: the role of polycyclic aromatic hydrocarbons.},

author = {Zdeněk Andrysík and Jan Vondráček and Soňa Marvanová and Miroslav Ciganek and Jiří Neča and Kateřina Pěnčíková and Brinda Mahadevan and Jan Topinka and William M. Baird and Alois Kozubík and Miroslav Machala},

doi = {10.1016/j.mrfmmm.2011.06.011},

issn = {0027-5107},

year  = {2011},

date = {2011-09-01},

journal = {Mutation research},

volume = {714},

number = {1-2},

pages = {53–62},

abstract = {Many of the toxic and carcinogenic effects of urban air pollution have been linked to polycyclic aromatic hydrocarbons (PAHs) adsorbed to airborne particulate matter (PM). The carcinogenic properties of PAHs in complex organic mixtures derived from PM have been chiefly attributed to their mutagenicity. Nevertheless, PAHs are also potent activators of the aryl hydrocarbon receptor (AhR), which may contribute to their nongenotoxic effects, including tumor promotion. As the genotoxicity of carcinogenic PAHs in complex mixtures derived from urban PM is often inhibited by other mixture constituents, the AhR-mediated activity of urban PM extracts might significantly contribute to the carcinogenic activity of such mixtures. In the present study, we used an organic extract of the urban dust standard reference material, SRM1649a, as a model mixture to study a range of toxic effects related to DNA damage and AhR activation. Both the organic extract and its neutral aromatic fraction formed a low number of DNA adducts per nucleotide in the liver epithelial WB-F344 cells model, without inducing DNA damage response, such as tumor suppressor p53 activation and apoptosis. In contrast, we found that this extract, as well as its neutral and polar fractions, were potent inducers of a range of AhR-mediated responses, including induction of the AhR-mediated transcription, such as cytochrome P450 1A1/1B1 expression, and the AhR-dependent cell proliferation. Importantly, these toxic events occurred at doses one order of magnitude lower than DNA damage. The AhR-mediated activity of the neutral fraction was linked to PAHs and their derivatives, as polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls were only minor contributors to the overall AhR-mediated activity. Taken together, our data suggest that more attention should be paid to the AhR-dependent nongenotoxic events elicited by urban PM constituents, especially PAHs and their derivatives.},

note = {Place: Netherlands},

keywords = {Animals, Apoptosis/drug effects, Aryl Hydrocarbon/*metabolism, Cell Line, Cell Proliferation/drug effects, Cytochrome P-450 CYP1A1/metabolism, DNA Adducts/drug effects, DNA Damage/*drug effects, Dose-Response Relationship, Drug, Genes, Liver/drug effects, Mutagens/*toxicity, Organic Chemicals/*toxicity, p53/drug effects, Particulate Matter/*toxicity, Polycyclic Aromatic Hydrocarbons/*toxicity, Rats, Receptors},

pubstate = {published},

tppubtype = {article}

}

@article{trilecova_toxic_2011,

title = {Toxic effects of methylated benzo[a]pyrenes in rat liver stem-like cells.},

author = {Lenka Trilecová and Simona Krčková and Soňa Marvanová and Kateřina Pĕnčíková and Pavel Krčmář and Jiří Neča and Petra Hulinková and Lenka Pálková and Miroslav Ciganek and Alena Milcová and Jan Topinka and Jan Vondráček and Miroslav Machala},

doi = {10.1021/tx200049x},

issn = {1520-5010 0893-228X},

year  = {2011},

date = {2011-06-01},

journal = {Chemical research in toxicology},

volume = {24},

number = {6},

pages = {866–876},

abstract = {The methylated benzo[a]pyrenes (MeBaPs) are present at significant levels in the environment, especially in the sediments contaminated by petrogenic PAHs. However, the existing data on their toxic effects in vitro and/or in vivo are still largely incomplete. Transcription factor AhR plays a key role in the metabolic activation of PAHs to genotoxic metabolites, but the AhR activation may also contribute to the tumor promoting effects of PAHs. In this study, the AhR-mediated activity of five selected MeBaP isomers was estimated in the DR-CALUX reporter gene assay performed in rat hepatoma cells. Detection of other effects, including induction of CYP1A1, CYP1B1, and AKR1C9 mRNAs, DNA adduct formation, production of reactive oxygen species, oxidation of deoxyguanosine, and cell cycle modulation and apoptosis, was performed in the rat liver epithelial WB-F344 cell line, a model of liver progenitor cells. We identified 1-MeBaP as the most potent inducer of AhR activation, stable DNA adduct formation, checkpoint kinase 1 and p53 phosphorylation, and apoptosis. These effects suggest that 1-MeBaP is a potent genotoxin eliciting a typical sequence of events ascribed to carcinogenic PAHs: induction of CYP1 enzymes, formation of high levels of DNA adducts, activation of DNA damage responses (including p53 phosphorylation), and cell death. In contrast, 10-MeBaP, representing BaP isomers substituted with the methyl group in the angular ring, elicited only low levels DNA adduct formation and apoptosis. Other MeBaPs under study also elicited strong apoptotic responses associated with DNA adduct formation as the prevalent mode of toxic action of these compounds in liver cells. MeBaPs induced a weak production of ROS, which did not lead to significant oxidative DNA damage. Importantly, 1-MeBaP and 3-MeBaP were found to be potent AhR agonists, one order of magnitude more potent than BaP, thus suggesting that the AhR-dependent modulations of gene expression, deregulation of cell survival mechanisms, and further nongenotoxic effects associated with AhR activation may further contribute to their tumor promotion and carcinogenicity.},

note = {Place: United States},

keywords = {Animals, Apoptosis/drug effects, Aryl Hydrocarbon/*metabolism, Benzo(a)pyrene/*chemistry/*toxicity, Cell Cycle/drug effects, Cell Line, Checkpoint Kinase 1, DNA Adducts/metabolism, Epithelial Cells/drug effects/metabolism, Gene Expression Regulation/drug effects, Liver/*cytology, Methylation, Mutagens/*chemistry/*toxicity, Oxidative Stress/drug effects, Protein Kinases/metabolism, Rats, Receptors, Stem Cells/drug effects/metabolism, Tumor, Tumor Suppressor Protein p53/metabolism},

pubstate = {published},

tppubtype = {article}

}

@article{vondracek_role_2009,

title = {The role of aryl hydrocarbon receptor in regulation of enzymes involved in metabolic activation of polycyclic aromatic hydrocarbons in a model of rat liver progenitor cells.},

author = {Jan Vondrácek and Pavel Krcmár and Jirina Procházková and Lenka Trilecová and Martina Gavelová and Lenka Skálová and Barbora Szotáková and Martin Buncek and Hana Radilová and Alois Kozubík and Miroslav Machala},

doi = {10.1016/j.cbi.2009.03.011},

issn = {1872-7786 0009-2797},

year  = {2009},

date = {2009-07-01},

journal = {Chemico-biological interactions},

volume = {180},

number = {2},

pages = {226–237},

abstract = {In contrast to hepatocytes, there is only limited information about the expression and activities of enzymes participating in metabolic activation of environmental mutagens, including polycyclic aromatic hydrocarbons (PAHs), in liver progenitor cells. In rat liver "stem-like" WB-F344 cell line, sharing many characteristics with rat liver progenitor cells, PAHs are efficiently activated to their ultimate genotoxic metabolites forming DNA adducts. The present study aimed to characterize expression/activities of enzymes of two major pathways involved in the metabolism of benzo[a]pyrene (BaP): cytochrome P450 (CYP) family 1 enzymes and cytosolic aldo-keto reductases (AKRs). We report here that, apart from induction of CYP1A1 and CYP1B1 expression and the corresponding enzymatic activity, both BaP and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced rat 3alpha-hydroxysteroid dehydrogenase (AKR1C9) expression and activity. In contrast, the aldehyde reductase AKR1A1 was not induced by either treatment. Thus, both CYP1 and AKR metabolic pathways were inducible in the model of liver progenitor cells. BaP and TCDD were efficient inducers of NAD(P)H:quinone oxidoreductase 1 (NQO1) expression and activity in WB-F344 cells, a principal enzyme of cellular antioxidant defense. Both compounds also induced expression of transcription factor NRF2, involved in control of enzymes protecting cells from oxidative stress. However, although BaP induced a significant formation of reactive oxygen species, it did not induce expression of heme oxygenase-1, suggesting that induction of oxidative stress by BaP was limited. Using shRNA against the aryl hydrocarbon receptor (AhR), we found that similar to CYP1A1 and CYP1B1, the AKR1C9 induction was AhR-dependent. Moreover, constitutive AKR1C9 levels in AhR-deficient rat BP8 hepatoma cells were significantly lower than in their AhR-positive 5L variant, thus supporting possible role of AhR in regulation of AKR1C9 expression. Taken together, both CYP1 and AKR1C9 appear to be AhR-regulated metabolic pathways, which may contribute to formation of pro-carcinogenic PAH metabolites in liver progenitor cells.},

note = {Place: Ireland},

keywords = {Animals, Aryl Hydrocarbon/*metabolism, Benzo(a)pyrene/toxicity, Cell Line, Dimethyl Sulfoxide/toxicity, Enzymologic/drug effects, Gene Expression Regulation, Gene Silencing, Hydrogen Peroxide/toxicity, Liver/*cytology/*enzymology, Polychlorinated Dibenzodioxins/analogs & derivatives/toxicity, Polycyclic Aromatic Hydrocarbons/*metabolism, Rats, Reactive Oxygen Species, Receptors, Stem Cells/*drug effects/*metabolism},

pubstate = {published},

tppubtype = {article}

}

@article{pliskova_effects_2005,

title = {Effects of silymarin flavonolignans and synthetic silybin derivatives on estrogen and aryl hydrocarbon receptor activation.},

author = {Martina Plísková and Jan Vondrácek and Vladimír Kren and Radek Gazák and Petr Sedmera and Daniela Walterová and Jitka Psotová and Vilím Simánek and Miroslav Machala},

doi = {10.1016/j.tox.2005.06.020},

issn = {0300-483X},

year  = {2005},

date = {2005-11-01},

journal = {Toxicology},

volume = {215},

number = {1-2},

pages = {80–89},

abstract = {Silymarin, a standardized mixture of flavonolignans, or its major constituents could be effective for prevention and treatment of hepatic damage or skin cancer. However, their potential side effects, such as modulation of endocrine functions via the disruption of estrogen receptor (ER) and/or aryl hydrocarbon receptor (AhR) activation, are largely unknown. In the present study, we investigated impact of silymarin, its constituents and a series of their synthetic derivatives on ER- and AhR-mediated activities using in vitro reporter gene assays. We found that none of the compounds under study affected the AhR-mediated activity in rat hepatoma cells. Contrary to that, several compounds behaved as either partial or full ER agonists. Silymarin elicited partial ER activation, with silybin B being probably responsible for a majority of the weak ER-mediated activity of silymarin; silybin A and other flavonolignans were found to be inactive and potent ER agonist taxifolin is only a minor constituent of silymarin. To our knowledge, this is probably the first time, when receptor-specific in vitro effects of separated diastereomers have been demonstrated. In contrast to silymarin constituents, the synthetic silybin derivatives, potentially useful as chemoprotective agents, did not modulate the ER-mediated activity, with exception of 23-O-pivaloylsilybin. Interestingly, 7-O-benzylsilybin potentiated ER-mediated activity of 17beta-estradiol despite possessing no estrogenic activity. In conclusion, our data suggest that estrogenicity of some silymarin constituents should be taken in account as their potential side effect when considered as chemopreventive compounds. These results also stress the need to study biological activities of purified or synthesized diastereomers of silybin derivatives.},

note = {Place: Ireland},

keywords = {Animals, Aryl Hydrocarbon/*metabolism, Cell Line, Cell Survival/drug effects, Dose-Response Relationship, Drug, Estrogen/*metabolism, Humans, Luciferases/biosynthesis/genetics, Molecular Structure, Rats, Receptors, Silybin, Silymarin/chemistry/pharmacology, Stereoisomerism, Tumor},

pubstate = {published},

tppubtype = {article}

}

@article{vondracek_aryl_2005,

title = {Aryl hydrocarbon receptor-activating polychlorinated biphenyls and their hydroxylated metabolites induce cell proliferation in contact-inhibited rat liver epithelial cells.},

author = {Jan Vondrácek and Miroslav Machala and Vítezslav Bryja and Katerina Chramostová and Pavel Krcmár and Cornelia Dietrich and Ales Hampl and Alois Kozubík},

doi = {10.1093/toxsci/kfi009},

issn = {1096-6080 1096-0929},

year  = {2005},

date = {2005-01-01},

journal = {Toxicological sciences : an official journal of the Society of Toxicology},

volume = {83},

number = {1},

pages = {53–63},

abstract = {Polychlorinated biphenyls (PCBs) exhibit tumor-promoting effects in experimental animals. We investigated effects of six model PCB congeners and hydroxylated PCB metabolites on proliferation of contact-inhibited rat liver epithelial WB-F344 cells. The 'dioxin-like' PCB congeners, PCB 126, PCB 105, and 4'-OH-PCB 79, a metabolite of the planar PCB 77 congener, induced cell proliferation in a concentration-dependent manner. In contrast, the 'non-dioxin-like' compounds that are not aryl hydrocarbon receptor (AhR) agonists, PCB 47, PCB 153, and 4-OH-PCB 187, an abundant noncoplanar PCB metabolite, had no effect on cell proliferation at concentrations up to 10 muM. The concentrations of dioxin-like PCBs leading to cell proliferation corresponded with the levels inducing the expression of cytochrome P450 1A1 mRNA, suggesting that the release from contact inhibition was associated with AhR activation. The effects of PCB 126 and PCB 153 on expression of proteins controlling G0/G1-S-phase transition and S-phase progression were compared. Only PCB 126 was found to upregulate cyclin A and D2 protein levels, and to increase both total cyclin-dependent kinase 2 (cdk2) and cyclin A/cdk2 complex activities. Despite the observed upregulation of cyclin D2, no increase in cdk4 activity was observed. The expression of cdk inhibitor p27Kip1 was not affected by either PCB 126 or PCB 153. These results suggest that dioxin-like PCBs can induce cell proliferation of contact-inhibited rat liver epithelial cells by increasing cyclin A protein levels, a process that then leads to upregulation of cyclin A/cdk2 activity and initiation of DNA replication. This mechanism could be involved in tumor-promoting effects of dioxin-like PCBs.},

note = {Place: United States},

keywords = {Animals, Aryl Hydrocarbon/*metabolism, Cell Line, Cell Proliferation/*drug effects, Cyclin A/biosynthesis, Cyclin D2, Cyclin-Dependent Kinases/biosynthesis, Cyclins/biosynthesis, Dose-Response Relationship, Drug, Epithelial Cells/*drug effects/enzymology/metabolism, Hydroxylation, Liver/*cytology, Polychlorinated Biphenyls/metabolism/*toxicity, Rats, Receptors, Stem Cells/*drug effects/enzymology/metabolism, Up-Regulation},

pubstate = {published},

tppubtype = {article}

}