Particulate matter toxicity and health effects : in vitro assessment of the mechanisms of action

Urban airborne particulate matter (PM) is known to increase morbidity and mortality due to cardiopulmonary diseases related to inflammatory processes and genotoxic effects. The study of PM-induced toxicity represents a very important field in order to understand the clinical outcomes and define the most harmful components involved. Despite the researchers’ effort, there are still unresolved questions regarding the cell mechanisms inducing the different adverse effects. Moreover, which PM components are more significant in determining the biological responses is still a debated question, although this aspect is of primary importance for the individuation of the most impacting sources, which have to be regulated. Thus, the aims of this thesis were - the analysis of the biological effects induced by PM exposure in cell lines representative of the lung apparatus, to evaluate the role of season, location and size of particles - the understanding of the mechanisms and molecular pathways activated by Milan PM fractions with particular attention to winter PM2.5, linking the outcomes to the particles physical and chemical properties. The results obtained demonstrated that the PM-induced biological effects were related to the site and season of sampling, and directly linked to the specific PM chemical composition. The PMs size was another significant factor in eliciting the toxic potential, not only for the chemical composition of particles of diverse dimension, but also for a different bioavailability of the compounds adsorbed, which is higher for the finest fractions. In particular, summer PM10 resulted to be the most cytotoxic and pro-inflammatory fraction for its high content of endotoxins and metals, known inducers of both these biological effects. Winter PMs, especially the fine ones (PM2.5, PM1 and PM0.4), produced a genotoxic effect and caused alterations of the cell cycle through the induction of DNA damage and acting as mitotic spindle poisons. Organic components, in particular PAHs, were responsible of such effects through ROS production and CYP enzymes-mediated reactive molecules formation. A peculiar aspect evidenced was the formation of abnormal mitotic spindles, and in particular the presence of tripolar spindles, which were able to satisfy the spindle assembly checkpoint and perform cell division. The data reported provide a significant contribution to the knowledge of PM toxicity, describing biological processes that can be involved in the clinical and epidemiological observations widely reported; however a complete understanding of the mechanisms of action at cell level still lacks. A further insight in the comprehension of PM health impact may derive by further investigations on different cell lines, cultures of primary pulmonary cells and by the assembly of an alveolar-capillary barrier for the study of the particles systemic effects.