Abstract
Abstract: Background Epidemiological studies, together with experimental studies, have shown a causal relationship between exposure to particulate matter (PM) and elevated morbidity and mortality of respiratory diseases. PM sampled from road tunnel contains particles originate from various sources, including vehicle exhaust, tire wear, and pavement erosion. In the present study, we aimed to examine the pro-inflammatory potency of coarse, fine, and ultrafine (UF) PM, collected from Hell road tunnel in Trondheim, compared to the quartz diorite stone particles used in the pavement of the tunnel and diesel exhaust particles (DEP). Methods The Phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 cells (THP-1 macrophages) were exposed to coarse, fine, and UF fraction of tunnel particles and quartz diorite and DEP for 20 hours. The supernatants were collected and analysed for the cytokine release of CXCL8, IL-1β, and TNFα with Enzyme Linked Immunosorbent Assay (ELISA). At the same time, the cells were harvested, and the messenger RNA (mRNA) expression of CXCL8, IL-1β, TNFα, COX-2, CYP1A1, AhR, and HO-1 was assessed in real-time Reverse Transcriptase Polymerase Chain Reaction (real-time RT-PCR). In addition, the metabolic activity and cytotoxicity of THP-1 macrophages after exposure to different PM were examined by AlamarBlue assay and lactate dehydrogenase (LDH) assay, respectively. Results THP-1 macrophages exposed to PM samples secreted increasing cytokine levels in a concentration- and time-dependent manner, except for quartz diorite and DEP. The pro-inflammatory responses to fine PM were significantly higher for the fine than coarse and ultrafine PM. Furthermore, the responses to all size fractions of tunnel-derived particles were much higher than for quartz diorite and DEP, as reflected in the cytokine responses of CXCL8, IL-1β, and TNFα at the protein and possibly also the gene expression levels. There were observed only slight and insignificant reductions in cytokine release after the addition of AhR antagonist (CH223191) and antioxidant (NAC). Overall, the cell viability, as measured by metabolic activity and LDH release, was affected only to a relatively small extent. Conclusion The pro-inflammatory effects of road tunnel PM were markedly higher than individual constituents PM of quartz diorite and DEP in THP-1 macrophages, suggesting that stone particles and DEP are not the major contributors of the tunnel PM responses. Furthermore, the pro-inflammatory responses seemed not to involve AhR- or ROS-dependent pathways, suggesting that organic compounds do not contribute to cytokine generation.