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

Abstract

The occupational exposure to particles such as crystalline quartz and its impact on the respiratory tract have been studied extensively in recent years. For hazard assessment, the development of physiologically more relevant in-vitro models, i.e., air-liquid interface (ALI) cell cultures, has greatly progressed. Within this study, pulmonary culture models employing A549 and differentiated THP-1 cells as mono-and co-cultures were investigated. The different cultures were exposed to α-quartz particles (Min-U-Sil5) with doses ranging from 15 to 66 µg/cm2 under submerged and ALI conditions and cytotoxicity as well as cytokine release were analyzed. No cytotoxicity was observed after ALI exposure. Contrarily, Min-U-Sil5 was cytotoxic at the highest dose in both submerged mono- and co-cultures. A concentration-dependent release of interleukin-8 was shown for both exposure types, which was overall stronger in co-cultures. Our findings showed considerable differences in the toxicological responses between ALI and submerged exposure and between mono- and co-cultures. A substantial influence of the presence or absence of serum in cell culture media was noted as well. Within this study, the submerged culture was revealed to be more sensitive. This shows the importance of considering different culture and exposure models and highlights the relevance of communication between different cell types for toxicological investigations.

Gene Expression Profiling of Mono- and Co-Culture Models of the Respiratory Tract Exposed to Crystalline Quartz under Submerged and Air-Liquid Interface Conditions

“…The doses for submerged exposures were chosen correspondingly; here, the total deposited doses were considered to comply with the applied nominal doses based on particle size and their rapid sedimentation, which has previously been described in other studies [ 30 ]. Regarding dTHP-1 cells, lower doses were applied due to the higher cytotoxicity when compared to A549 cells [ 27 ]. Furthermore, ALI exposure experiments were not performed with this cell line as these cells do not build a confluent monolayer.…”

“…In this study, we applied a co-culture model comprised of the alveolar epithelial cell line A549 and differentiated macrophage-like dTHP-1 cells to investigate the transcriptional toxicity profiles of quartz particles, following up on a recent report evaluating cytotoxicity and cytokine release after quartz exposure using the same cell culture models [ 27 ]. Within this study, it was our objective to assess potential differences between the co-culture model and the corresponding mono-cultures as well as the classical submerged vs. the ALI exposure with regard to the transcriptional response induced by a well-known test substance, the α-quartz Min-U-Sil5.…”

“…Generally speaking, the effects of Min-U-Sil5 on the gene expression profiles of the applied cell models were rather modest when compared to highly toxic particles such as copper oxide [ 36 , 37 , 38 , 39 ]. This is especially evident considering the high quartz doses, which were able to produce a strong concentration-dependent cytotoxicity in dTHP-1 cells and a moderate cytotoxicity in A549 mono- and A549/dTHP-1 co-cultures under submerged conditions [ 27 ]. The gene induced most strongly after 24 h was IL-8, with an 8-fold, 32-fold, and 16-fold induction in submerged A549 mono-cultures, dTHP-1 mono-cultures and A549/dTHP-1 co-cultures, respectively.…”

“…Furthermore, TEM was performed with a UM910 microscope (Zeiss, Oberkochen, Germany). The results from the DLS measurements as well as the TEM images have already been published in our previous work [ 27 ].…”

“…The particles used for this study were characterized via dynamic light scattering (DLS) und transmission electron microscopy (TEM), which revealed a broad size distribution, peaking at a diameter of 0.95 µm. Its purity of 99.4% and high crystallinity qualified Min-U-Sil5 for mechanistic toxicity studies as well [ 27 ]. Within the present study, we aimed to elucidate underlying molecular mechanisms and signaling pathways triggered by quartz, utilizing the same quartz particles.…”