Toxicology of urban particulate matter: In vitro and in vivo bioassays

Exposure to air particulate matter (PM) is epidemiologically associated with increased incidence of respiratory and cardiovascular disease in humans. Although inflammation, oxidative stress and toxicity have been implicated in the pathophysiological response to air pollution, the physicochemical properties of the particles responsible for the adverse effects are yet to be elucidated. In vitro assays are widely used to study the toxicity of particles, however, they have not been comprehensively validated in vivo. This work aimed to evaluate in vitro cytotoxicity and inflammatory cytokine assays as screening tools for relative toxicity of PM, validate their capacity to predict toxicity of PM in BALB/c mice, develop a cell-interaction model for the study of the biological effects of PM, and evaluate its performance in relation to PM effects in animals. Results show that in vitro assays conducted in macrophage (J774A.1) and alveolar epithelial (A549) cell lines can discriminate between PM, based on their cytotoxic and inflammatory potency. SRM- and EHG-type particles were more potent than DWR1 (PM2.5) and mineral particles both in vitro and in vivo, although PM rankings varied considerably between assays. PM with different compositions had different toxic potencies. Combinations of 2 to 4 in vitro assays showed a predictive potential for PM-induced effects in vivo, represented by bronchoalveolar lavage (BAL) neutrophilia in mice. In a co-culture, epithelial (A549) and macrophage (THP-1) cells synergistically modulate their production of pro-inflammatory cytokines (IL-1beta, IL-6, IL-8, MCP-1 and TNF-alpha), ICAM-1 and VEGF in response to PM exposure. Cellular mediators from PM-exposed co-cultures can activate endothelial cells (HPAE) to produce cytokines (IL-6, IL-8, GM-CSF, MCP-1) and adhesion factors (ICAM-1, VCAM-1 and E-selectin). Exposure of mice to EHG6802, DWR1 and SRM-1650 particles led to BAL neutrophilia and elevated cytokines (IL-6, KC, MIP-1alpha, TNF-alpha, with a stronger inflammatory response at 2 hrs then 24 hrs. Statistical comparison of the cell interaction model responses with PM-induced BAL neutrophilia in vivo shows that the co-culture model correlates well with biological effects of particles in mice. Along with its ability to simulate physiologically relevant cell-cell interactions, it is a good model for studying mechanisms of PM toxicity, and for relative toxicity screening of particles