Cytotoxicity and genotoxicity of urban particulate matter in mammalian cells

Ambient air particulate matter (PM)-associated reactive oxygen species (ROS) have been linked to a variety of altered cellular outcomes. In this study, three different PM samples from diesel exhaust particles (DEPs), urban dust standard reference material SRM1649a and air collected in Manchester have been tested for their ability to oxidise DNA in a cell-free assay, to increase intracellular ROS levels and to induce CYP1A1 gene expression in mammalian cells. In addition, the cytotoxicity and genotoxicity of PM were assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and alkaline comet assay, respectively. All PM samples catalysed the Fenton reaction in a cell-free assay, but only DEP resulted in the generation of ROS as measured by dichlorodihydrofluorescein diacetate oxidation in mammalian cells. However, there was no evidence that increased ROS was a consequence of polycyclic aromatic hydrocarbon metabolism via CYP1A1 induction as urban dust, the Manchester dust samples but not DEP-induced CYP1A1 expression. Urban dust was more cytotoxic in murine embryonic fibroblasts (MEFs) than the other PM samples and also induced expression of GADD45a in the GreenScreen Human Cell assay without S9 activation suggesting the presence of a direct-acting genotoxicant. Urban dust and DEP produced comparable levels of DNA damage, as assessed by the alkaline comet assay, in MEFs at higher levels than those induced by Manchester PM. In conclusion, results from the cytotoxic and genotoxic assays are not consistent with ROS production being the sole determinant of PM-induced toxicity. This suggests that the organic component can contribute significantly to this toxicity and that further work is required to to better characterise the extent to which ROS and organic components contribute to PM-induced toxicity.