Évaluation du 4,5-dihydrodiol-benzo[a]pyrène et du 7,8-dihydrodiol-benzo[a]pyrène en tant que biomarqueurs spécifiques alternatifs d’exposition au benzo[a]pyrène

Benzo[a]pyrene (BaP) is one of the more commonly studied polycyclic aromatic hydrocarbons (PAHs), a group of omnipresent pollutants in the environment formed through incomplete combustion processes. It is listed as a confirmed carcinogen to human beings by the International Agency for Research on Cancer (IARC) and is highly present in many workplaces.  Although presenting a significant health risk to workers, there are currently no convenient compound-specific biomarkers that enable the tracking and monitoring of occupational exposure to BaP. 3-Hydroxybenzo[a]pyrene (3-OHBaP) is the most developed, as a biomarker, amongst the metabolites of BaP. It’s mostly excreted with the faeces, presenting in trace amounts in urine, which makes it difficult to measure; it is also demonstrates renal retention, which adds a layer of complexity in its use as a biomarker because there are many factors to take into consideration when looking at its kinetic time course. 1-Hydroxypyrene (1-OHP), in the other hand, is a urinary metabolite of pyrene that serves as a good representative of PAH presence. It is, however, the metabolite of a non-carcinogenic PAH, and is not fully capable of representing the cancer risk posed in a given scenario.  This thesis sought to detect and assess BaP exposure through tracking its urinary metabolites: 4,5-dihydrodiol-benzo[a]pyrene and 7,8-dihydrodiol-benzo[a]pyrene (4,5-diolBaP and 7,8-diolBaP; diolBaPs). 4,5-DiolBaP and 7,8-diolBaP were evaluated through two studies:  The first study, the “shampoo experiment”, featured a volunteer who self-exposed to PAHs in a controlled setting by using a coal-tar-based shampoo. The study consisted of two experiments. The first focused on a single exposure and the second on multiple exposures. This study was set to evaluate the time course of 7,8-diolBaP in humans and verifying its potential as a biomarker of exposure through a comparison with 1-OHP in the same experimental framework. The second study consisted of a comparative analysis of 4,5-diolBaP, 7,8-diolBaP, 1-OHP and 3-OHBaP in an occupational setting, evaluating the competency of the diolBaPs in a real-world setting alongside established biomarkers of BaP and PAH exposure. Five workers at a carbon anode production plant volunteered to participate in this study. For both of these studies, the urine samples were analysed by ultra-high-pressure liquid chromatography (UHPLC) coupled with fluorescence.  “Shampoo Experiment”: The single and multiple exposures revealed a monoexponential elimination on the part of 7,8-diolBaP, identical to 1-OHP, with similar magnitudes of concentration. 1-OHP was also confirmed to undergo a more rapid elimination from the system, where after each exposure for 7,8-diolBaP, the ensuing peak value is higher. This finding demonstrated evidence of accumulation of 7,8-diolBaP throughout the week, whereas with 1-OHP, the second peak is larger, then the third one is smaller, thus showing less accumulation over the same time frame.  “Worker Study”: The results showed that the analytical method used was unable to properly discern 4,5-diolBaP from other urinary contaminants eluting during the same retention time. 7,8-DiolBaP, on the other hand, eluted at urinary concentrations that were a similar order of magnitude to 1-OHP, as can be seen in all of the workers evaluated. For some workers, the urinary concentration of 7,8-diolBaP was consistently at its peak prior to the start of a shift and elimination took place during the shift, to provide a lower concentration value at the end of the shift. With 1-OHP, the rise was immediate with exposure, peaking at the end of every shift. For other workers, both 7,8-diolBaP and 1-OHP are consistently higher at the end of the shift. These variations are likely to indicate different routes of exposure. This thesis showed the potential use of 7,8-diolBaP as a compound-specific biomarker of exposure for BaP and thus provides a starting point in exploring the quantification of BaP exposure and negative health effects in humans. Confirmation of the compound’s identity is needed through the use of mass spectrometry.

Keyphrases: Benzo[a]pyrene, metabolism, biomarkers, toxicokinetics, 4,5-dihydrodiol-benzo[a]pyrene, 7,8-dihydrodiol-benzo[a]pyrene, 1-hydroxypyrene