Evalution of a challenge assay as na effect biomarker in environmental or occupational biomonitoring studies

Background: Human long-term exposure to environmental or occupational stressors may produce adverse effects, e.g., genotoxic effects that underlie the onset of diseases, among which cancer is the most severe. Besides the instability that a wide variety of genotoxic and carcinogenic agents directly exert on the cell genome, also indirect effects, e.g., interference with the DNA repair capacity deserve to be studied. Such effects have been described for heavy metals, low doses of ionising radiation or complex mixtures, among others. Aim: This work aimed to evaluate the usefulness of the ex vivo challenge assay as a functional biomarker of early biological effects, based on data previously obtained in molecular epidemiology studies. Methods: The first study (S1) comprised a group of individuals with environmental exposure to ionising radiation and heavy metals (IR Group) and a non-exposed group (NIR Group), whereas the second study (S2) included individuals occupationally exposed to environmental tobacco smoke (ETS Group) and the respective control group (NETS Group). In S1, whole blood samples were subjected to 2Gy of ionising radiation before culture set up for translocation analysis through FISH. Blood samples from S2 participants were exposed to an alkylating agent (EMS) and then processed for the comet assay; the level of DNA damage was quantified by the percentage of DNA in tail. The level of chromosome or DNA damage measured after the ex vivo challenge with the genotoxic agents was compared to the basal level obtained for the same individuals in S1 and S2, respectively. Results: The results from both studies showed that peripheral blood lymphocytes (PBLs) exposure to a medium/high dose of a genotoxicant (ionising radiation or EMS), followed by an assessment of chromosome or DNA damage, respectively, allowed to distinguish exposed and control groups. The distinct response consisted of a lower frequency of ionising radiation-induced translocations in the IR comparatively to the NIR group (S1) or a lower level of EMS-induced DNA breaks in the ETS comparatively to the NETS Group (S2). Discussion and Conclusions: The results from both studies agreed in that the use of an ex vivo challenge of PBLs with a genotoxicant allowed the detection of a differential response between the exposed and non-exposed groups. Interestingly, PBLs from exposed individuals were less affected by the ex vivo exposure to a genotoxicant suggesting an adaptive response instead of a reduced DNA repair capacity. These findings are expected to contribute to the development of new biomarkers of early biological effects for human biomonitoring studies.Portuguese Ministry of Health, Calouste Gulbenkian Foundation and Foundation for Science and Technology - ToxOmics (UID/BIM/00009/2013)N/