Toxic Effects of the Major Components of Diesel Exhaust in Human Alveolar Basal Epithelial Cells (A549)

Abstract

We investigated the toxicity of benzo[a]pyrene (B[a]P), 1-nitropyrene (1-NP) and 3-nitrobenzanthrone (3-NBA) in A549 cells. Cells were treated for 4 h and 24 h with: B[a]P (0.1 and 1 μM), 1-NP (1 and 10 μM) and 3-NBA (0.5 and 5 μM). Bulky DNA adducts, lipid peroxidation, DNA and protein oxidation and mRNA expression of CYP1A1, CYP1B1, NQO1, POR, AKR1C2 and COX2 were analyzed. Bulky DNA adducts were induced after both treatment periods; the effect of 1-NP was weak. 3-NBA induced high levels of bulky DNA adducts even after 4-h treatment, suggesting rapid metabolic activation. Oxidative DNA damage was not affected. 1-NP caused protein oxidation and weak induction of lipid peroxidation after 4-h incubation. 3-NBA induced lipid peroxidation after 24-h treatment. Unlike B[a]P, induction of the aryl hydrocarbon receptor, measured as mRNA expression levels of CYP1A1 and CYP1B1, was low after treatment with polycyclic aromatic hydrocarbon (PAH) nitro-derivatives. All test compounds induced mRNA expression of NQO1, POR, and AKR1C2 after 24-h treatment. AKR1C2 expression indicates involvement of processes associated with reactive oxygen species generation. This was supported further by COX2 expression induced by 24-h treatment with 1-NP. In summary, 3-NBA was the most potent genotoxicant, whereas 1-NP exhibited the strongest oxidative properties.

Genotoxicity of fine and coarse fraction ambient particulate matter in immortalised normal (TT1) and cancer‐derived (A549) alveolar epithelial cells

“…Levels of BaP‐DNA adducts in TT1 cells were 66‐fold lower than 3‐NBA‐DNA adducts. It is noteworthy that the observed BaP‐DNA adduct levels in TT1 cells are low compared to other published studies [Hockley et al, ; Rossner et al, ; Shi et al, ]. In this study, we showed induction of CYP1A1 in TT1 cells and not a genotoxic response, and hence, this might be reflective of increased repair of BaP‐DNA adducts in the TT1 cell line in the timeframe studied, or a stronger detoxifying effect of CYP1A1; further work is warranted to understand this.…”

“…Finally, the concentrations used in the study are higher than humans would be exposed to under realistic exposure scenarios. For example, Rossner et al [] suggested that for an ambient concentration of BaP of 0.1–10 ng/m 3 in air this would represent femtomolar concentrations of BaP in culture medium. On the other hand, human lungs are typically chronically exposed to low levels of air pollutants, which is difficult to mimic in any cell culture models.…”

Environmental carcinogenesis and pH homeostasis: Not only a matter of dysregulated metabolism

“…In general, most of the parent compounds are detoxified. However, PAH metabolism can be harmful to cells, through the production of highly reactive electrophilic metabolites as well as reactive oxygen species (ROS) which then damage cellular macromolecules such as DNA, lipids or proteins [39][40][41][42][43]. The diol-epoxide metabolites are considered to be the most mutagenic and tumorigenic, notably through the formation of DNA-adducts [44][45][46].…”

“…The diol-epoxide metabolites are considered to be the most mutagenic and tumorigenic, notably through the formation of DNA-adducts [44][45][46]. In addition, the related ROS production may also lead to DNA damage [47,48], through the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) [39,41,43]. Both types of DNA damages, if not repaired, may then lead to important consequences in terms of DNA mutations [43][44][45][46], or to activation of cell death processes [49].…”

Nrf2 and AhR in metabolic reprogramming after contaminant exposure

“…However, AhR is a mediator of the toxicity for several xenobiotics: the PAH prototype benzo[a]pyrene (Ba[P]) is rapidly metabolized by cytochromes P450 and aldo-keto reductases and produces diol-epoxide metabolites that are mutagenic and tumorigenic, notably through the formation of DNA-adducts [10]. Moreover, AhR-dependent detoxification leads to oxidative stress and reactive oxygen species (ROS) production resulting in oxidative damage on cellular macro-molecules such as DNA, lipids or proteins [11][12][13].…”