Exploring the health impacts of the organic fraction of PM2.5: uncovering novel biomarkers of exposure through in vitro and ex vivo models

This PhD project focuses on the identification of novel biomarkers associated with exposure to urban atmospheric particulate matter (PM), with the overarching goal of defining molecular indicators capable of charactere health risks and supporting preventive strategies. Air pollution is a complex and dynamic mixture of solid particles, liquid droplets, and gases arising from numerous anthropogenic sources, such as industrial emissions, vehicular exhaust, agricultural practices, and waste combustion. Among these pollutants, fine particulate matter (PM₂.₅) plays a central role due to its ability to penetrate deep into the respiratory tract, enter the bloodstream, and reach multiple organs. Classified by the International Agency for Research on Cancer as a Group 1 human carcinogen, PM₂.₅ is strongly linked to respiratory and cardiovascular diseases through mechanisms involving oxidative stress, genotoxicity, inflammation, and cell death. In this context, my research investigated the biological effects of the organic fraction of PM₂.₅ on different cellular models in order to explore its potential involvement in chronic diseases such as pulmonary fibrosis and atherosclerosis. PM₂.₅ samples collected from suburban areas characterized by distinct pollution sources were chemically extracted and tested for mutagenic potential. Although not overtly genotoxic, the samples were found to be mildly mutagenic in Ames tests and able to induce oxidative stress and inflammatory responses in exposed cells. In lung fibroblasts, exposure to these extracts led to a significant production of reactive oxygen species (ROS) and modulation of pro-inflammatory cytokines (IL-6, IL-8, TNF-α), without affecting cell viability, suggesting that particulate chemical composition strongly influences toxicological outcomes. To further investigate cardiovascular implications, macrophage models were employed to study the effects of PM₂.₅ exposure on inflammation and lipid metabolism. The results showed that both PM₂.₅ extracts triggered ROS production and cytokine release and modulated the expression of genes involved in foam cell formation, including CD36, SRA1, ABCA1, and ABCG1. These findings support the hypothesis that chronic exposure to low concentrations of particulate matter may not cause acute cytotoxicity but can alter key regulatory pathways linked to the development of atherosclerosis. Further experiments on primary peritoneal macrophages confirmed that PM₂.₅ induces differential cytokine release depending on macrophage activation state and exposure duration, revealing complex dose–response dynamics that may reflect hormetic effects. Overall, this work contributes to a deeper understanding of how exposure to atmospheric particulate matter influences cellular oxidative and inflammatory processes and highlights the potential of specific molecular markers to serve as early indicators of environmentally induced pathologies.