PhD defense of Maguy EL HAJJAR from TIMC EPSP team at monday, the 26th of june, 1:30pm:

" Study of changes in the metabolism of polycyclic aromatic hydrocarbons in mixtures in a rat model. "
 

Jury :

• Christine DEMEILLIERS, Maîtresse de conférences HDR, Université Grenoble Alpes, Supervisor
• Anne MAÎTRE, Professeure des Universités - Praticienne hospitalière, Université Grenoble Alpes, Co-supervisor
   
• Brigitte LEMAGUERESSE-BATTISTONI, Directrice de recherche, INSERM, Reporter
• Nancy HOPF, Chargée de Recherche HDR, Institut Santé Travail de Lausanne, Reporter
• Stéphane REYNAUD, Professeur des Universités, Université Grenoble Alpes, Examiner
• Lydie SPARFEL, Professeure des Universités, Université de Rennes1, Examiner

  Keywords

Polycyclic aromatic hydrocarbons ; Cocktail effect ; Benzo[a]pyrene ; Toxicokinetics ; Omics

  Abstract

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants produced in complex mixtures whose composition varies depending on the source of emission. High molecular weight (HMW) PAHs are classified as probable or possible human carcinogens by the International Agency for Research on Cancer (IARC) and benzo[a]pyrene (B[a]P) is the only PAH classified as a definite carcinogen. To exert their carcinogenic effect, PAHs must be metabolized. Biomonitoring of PAH exposure, which is very important for estimating health risks in populations, is done by analyzing urinary PAH metabolites. However, due to a lack of epidemiological data, there are no toxicological reference values (TRV) for these pollutants. Hence the importance of animal models to establish these TRVs.Thus the question arises: How to choose the right animal protocol to study the toxicokinetics of PAH in mixtures? Can genetic and environmental factors impact the results of these studies?
To answer these questions and to be able to extrapolate our results to humans, two animal protocols were carried out with realistic exposures (low doses, real mixture, short or repeated exposure). The first protocol consisted in exposing Sprague Dawley (SD) rats by gavage to low doses (0.02 and 0.2 mg.kg-1.d-1) of B[a]P alone or included in an industrial mixture of PAHs (adjusted to 0.2 mg.kg-1.d-1of B[a]P) 5 times.week-1 during 10 weeks. The second protocol consisted in exposing Wistar (W) rats by gavage to B[a]P alone (0.2 mg.kg-1.d-1) or included in an industrial mixture of PAHs (adjusted to 0.2 mg.kg-1.d-1 B[a]P) for 4 days. In addition to the determination of urinary metabolites of B[a]P and HMW PAHs, we developed the analysis of PAHs and/or their metabolites in blood, feces and organs (liver and kidneys) by HPLC-Fluo and GC-MSMS-NCI after different types of extraction depending on the matrices and compounds.
No difference in the toxicokinetics of B[a]P was found with the two doses used.
The mixture or cocktail effect was: increased absorption of B[a]P, altered intestinal metabolism with increased bioactivation pathway, decreased hepatic metabolism due to enzyme saturation/competition.
The effect of repeated exposure for 10 weeks was: increased PAH absorption after exposure to B[a]P and PAH mixture without change in intestinal metabolism, increased hepatic metabolism only after exposure to B[a]P alone at low dose (0.02 mg.kg-1.d-1).
The inter-strain variability between SD and W showed that the absorption and intestinal metabolism of fluoranthene and pyrene were identical between the 2 strains. However, absorption of HMW PAHs was lower in SD with intestinal metabolism of B[a]P directed toward the bioactivation pathway. Hepatic metabolism was higher in SD.
A large inter-individual variability was observed between W rats exposed to the PAH mixture in the intestinal absorption of HMW PAHs and their hepatic metabolism. There were different patterns of metabolite formation at the liver, whereas intestinal metabolism was comparable between rats.
Fasting increased the absorption of B[a]P but intestinal and hepatic metabolism were decreased and/or modified with an increase in the bioactivation pathway.
This work contributes to the reflection on the choice of the animal model and the exposure conditions for the determination of TRVs and the risk assessment of populations in a context of poly-exposures which is much more complex than a simple additive effect.