Australian bushfire-derived particulate matter and polycyclic aromatic hydrocarbons cause senescence and inflammation in precision cut lung slices

Introduction/Aim: Global warming has increased bushfires globally, releasing toxins Particulate Matter (PM) and Polycyclic Aromatic Hydro-carbons (PAHs). The effects of inhaled PMs and/or PAHs are under-studied. We investigated the harmful effects of PMs and/or PAHs from bushfire smoke exposure using precision cut lung slices (PCLS). We aimed to demonstrate size-dependent effects of PMs (1, 2.5, 10μm) and injurious effects of PM and/or PAHs in human and mouse PCLS, respectively.

Method: PCLS from human lung resections (hPCLS, 500μm, N = 3) were treated with media (control), PM1, PM2.5, or PM10 (5μg/ml) every 72h. PCLS from C57/BL6 mice (mPCLS, 400μm, N = 9) were treated with media, LPS (10 ng/mL; positive control), PM1 or PM2.5 (5 or 100 μg/mL); one or all PAHs (Fluoranthene, Phenanthrene, Pyrene, 100–1000μM); or PM2.5 alone or combined with PAHs for 24–48 h. Viability, senescence (immunohistochemistry p21), cytokines (IL-6, IL-8/KC, TNF-α, and IL-1β ELISAs) were assessed.

Results: PMs were viable without cytokine secretion (IL-6, IL-1β, and TNF-α) from hPCLS or mPCLS. PM2.5 and PM10 exposure, but not PM1, increased senescence >2-fold in hPCLS (p < 0.05 cf untreated). Combined PAHs (500 or 1000μM) caused death of mPCLS ( p < 0.05 and 0.01 cf untreated, respectively) so 300 μM PAHs were used. In mPCLS, KC(IL-8) secretion was induced by PAHs alone or in combination (300 μM), with Phenanthrene more potent than Fluoranthene and Pyrene. KC (IL-8) secretion in PAH-treated mPCLS was not further increased by adding PM2.5 (5 or 100 μg/mL).

Conclusion: We are the first to use translational PCLS to investigate the injurious effects of bushfire-derived PMs and PAHs. PMs induced size-dependent increases in senescence in hPCLS. Phenanthrene was the most potent PAH, selectively increasing IL-8 secretion suggestive of neutrophilic inflammation. Future studies should consider natural PM2.5 or PAH (i.e., smoked media) to validate bushfire smoke-induced lung injury contributions. We provide a strong public health message for forestry management in bushfire prone areas.