Crystalline silica particles cause rapid NLRP3-dependent mitochondrial depolarization and DNA damage in airway epithelial cells

Abstract

Background Respirable crystalline silica causes lung carcinomas and many thousand future cancer cases are expected in e.g. Europe. Critical questions are how silica causes genotoxicity in the respiratory epithelium and if new cases can be avoided by lowered permissible exposure levels. In this study we investigate early DNA damaging effects of low doses of silica particles in respiratory epithelial cells in vitro and in vivo in an effort to understand low-dose carcinogenic effects of silica particles. Results We find DNA damage accumulation already after 5–10 min exposure to low doses (5 μg/cm2) of silica particles (Min-U-Sil 5) in vitro. DNA damage was documented as increased levels of γH2AX, pCHK2, by Comet assay, AIM2 induction, and by increased DNA repair (non-homologous end joining) signaling. The DNA damage response (DDR) was not related to increased ROS levels, but to a NLRP3-dependent mitochondrial depolarization. Particles in contact with the plasma membrane elicited a Ser198 phosphorylation of NLRP3, co-localization of NLRP3 to mitochondria and depolarization. FCCP, a mitochondrial uncoupler, as well as overexpressed NLRP3 mimicked the silica-induced depolarization and the DNA damage response. A single inhalation of 25 μg silica particles gave a similar rapid DDR in mouse lung. Biomarkers (CC10 and GPRC5A) indicated an involvement of respiratory epithelial cells. Conclusions Our findings demonstrate a novel mode of action (MOA) for silica-induced DNA damage and mutagenic double strand breaks in airway epithelial cells. This MOA seems independent of particle uptake and of an involvement of macrophages. Our study might help defining models for estimating exposure levels without DNA damaging effects.

Comparing α-Quartz-Induced Cytotoxicity and Interleukin-8 Release in Pulmonary Mono- and Co-Cultures Exposed under Submerged and Air-Liquid Interface Conditions

“…All these results indicate the onset of a cytotoxic response starting at a dose of 60 µg/cm 2 Min-U-Sil5. Similar results of a low or absent cytotoxic response in A549 cells have been reported in several other studies for Min-U-Sil5 [ 39 , 40 ] or other quartz particles such as Norquartz [ 41 ], DQ12 [ 9 ], and NIST1878A [ 15 , 42 ]. In all these cases, cytotoxicity was apparent at a concentration of at least 50 µg/cm 2 , which is in line with our findings.…”

Coal Dust Exposure Triggers Heterogeneity of Transcriptional Profiles in Mouse Pneumoconiosis and Vitamin D Remedies

“…Previous studies have revealed that respirable particles lead to DNA damage once they move or remain in the pulmonary interstitium [55,56,57]. Our in vivo and in vitro study suggests that mouse AT2 cells undergo extensive stimulation and deformation during exposure to coal dust particles.…”

Responses of promyelocytic leukemia HL60 cells as an inflammatory cell lineage model to silica microparticles used to coat blood collection tubes

“…It is generally believed that the cytotoxicity of silica is attributable to the activity of reactive oxygen species (ROS) generated on the surface of silica particles [ 15 , 16 ]. ROS cause direct damage to the plasma membrane and DNA, thereby inducing cell death and tumor formation [ 17 – 19 ]. Given that the half-life of major ROS is relatively short (O •− 2 and 1 O 2 : 10 –6 s, OH • : 10 –9 s) [ 20 ], it is conjected that their detrimental effects are limited to cells that come into immediate contact with silica MPs.…”