The Extreme Variety of Genotoxic Response to Benzo[a]pyrene in Three Different Human Cell Lines from Three Different Organs

Camille Genies,Emmanuel Lefèbvre,Marianne Chopard-Lallier,Anne Maître,Thierry Douki,Amandine Jullien,Robert W Sobol

doi:10.1371/journal.pone.0078356

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are associated with occupational exposure and urban atmospheric pollution. Determination of the genotoxic properties of these compounds is thus of outmost importance. For this purpose a variety of cellular models have been widely used. Reliable results can however only be obtained with models reflecting the specific sensitivity of different organs towards PAHs. In this work, we compared the response to benzo[a]pyrene in cell lines from human lungs (A549) and bladder (T24); two important target organs for PAHs-induced cancer. Human hepatocytes (HepG2) were used as a reference, although liver is not a concern for PAHs carcinogenesis. Adducts arising from the ultimate diol-epoxide metabolite of B[a]P, BPDE, were found to be produced in a dose-dependent manner in HepG2. BPDE DNA adducts were not detected in T24 and in A549 their formation was found to be most efficient at the lowest concentration studied (0.2 µM). These results are probably explained by differences in induction and activity of phase I metabolization enzymes, as well as by proteins eliminating the B[a]P epoxide in A549. In addition to BPDE adducts, oxidative DNA damage, namely strand breaks and oxidized purines were measured and found to be produced only in minute amounts in all three cell lines. In summary, our results emphasize the large differences in the response of cells originating from different organs. Our data also point out the importance of carefully selecting the doses used in in vitro toxicological experiments. The example of A549 shows that working at high doses may lead to an underestimation of the risk. Finally, the choice of method for evaluating genotoxicity appears to be of crucial importance. The comet assay does not seem to be the best method for a compound like B[a]P which induces stable adducts causing limited oxidative damage.

Highlights

Atmospheric pollution concerns numerous occupations and the general population and includes a wide variety of chemical substances
While adduct formation was dose dependent for HepG2 from 0.2 to 5 mM, the pattern observed in A549 was a bell-shaped response (Fig 1A)
It should be emphasized that the amount of DNA adducts at 0.2 mM B[a]P was larger in A549 than in HepG2

Summary

Introduction

Atmospheric pollution concerns numerous occupations and the general population and includes a wide variety of chemical substances. The different PAHs are not all carcinogenic and basic toxicological data cannot be extrapolated from one to the other. Another specificity of PAHs is that they are always emitted in complex mixtures whose composition depends on the source. Animal studies appear to be powerful tools for this purpose. Such studies are cumbersome and expensive, and regulations tend to limit their use. In vitro approaches are attractive alternatives [5] Such investigations may be informative but should take into consideration the target organs of the studied compounds

Methods

Results

Discussion

Conclusion