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Génotoxicité des hydrocarbures aromatiques polycycliques en melanges, une classe majeure de polluants atmosphériques

Abstract : Polycyclic Aromatic Hydrocarbons (PAH) represent a family of ubiquitous atmospheric pollutants produced upon incomplete combustion and thus present in polluted atmosphere of the cities, in cigarette smoke and in certain industries. Exposure to HAP can cause lung, skin and bladder cancers. For this reason, some PAHs are suspected or recognized carcinogenic to humans, especially Benzo[a]pyrene (B[a]P), through their ability at inducing the formation of DNA damage after metabolization. In spite of the systematic emission of PAHs in mixtures, the majority of the studies was interested in the genotoxic effect of pure PAH and mainly B[a]P. In order to provide mechanistic data on the genotoxicity and the mode of action of PAH mixtures, we designed an in vitro study using cell lines representative of lungs (A549), bladder (T24) and liver (HepG2). DNA damage was investigated through the quantification of adducts by HPLC-MS/MS and of oxidative damage by the Comet assay. In addition, the metabolism was studied by analyzing genes induction by RT-qPCR and enzymatic activities of phase I CYP540 (EROD) and phase II (GST). First, the use of B[a] P, as a reference compound showed a quasi-total absence of metabolization and genotoxicity for T24. In contrast, the formation of DNA adducts formation and the induction of metabolization was highlighted for A549, with a bell-shaped dose-response curve similar to those observed in other lungs models. Then we extended this approach to 12 priority PAH and analyzed their metabolization and the possible formation of adducts focusing on the pulmonary cell line A549. The combination of these HAP to B[a]P in binary mixtures or in complex mixtures representative to environmental exposures led to a strong inhibition in adducts formation induced by B[a]P without outbreak of adducts from other PAH. In addition, we observed, in the case of complex mixtures, a good correlation between the EROD activity and the formation of adducts in DNA, while phase I genes were always overexpressed after exposure to mixtures when compared to pure B[a]P. The mechanisms involved in the inhibition of DNA adducts remain to be elucidated but PAHs metabolization represents a key step in the mixtures genotoxicity through inhibition or competition of CYP resulting in an inhibition of EROD activity. It is thus clear that the study of the HAP in an individual way is not sufficient to understand the genotoxicity of complex mixtures. The TEF Approach, usually used to asses the risk related to PAH mixtures exposure, relies on toxic effects additivity and ignores metabolic interactions between the various PAH. The improvement of this prediction tool is essential and involves necessarily the study of the underlying mechanisms which connect mixtures composition, their metabolization and their genotoxicity.
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Camille Genies. Génotoxicité des hydrocarbures aromatiques polycycliques en melanges, une classe majeure de polluants atmosphériques. Médecine humaine et pathologie. Université de Grenoble, 2013. Français. ⟨NNT : 2013GRENV053⟩. ⟨tel-01561073⟩

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