Evaluating the toxicity of polystyrene micro- and nanoplastics in human bronchial epithelial cells: differences and challenges using aerosol and suspension exposures.

Abstract

Objective: Studies investigating toxicity of airborne micro- and nanoplastics (MNPs) are mostly based on conventional submerged cell cultures while limited studies utilize air-liquid interface (ALI) systems. Inherent differences in these culture/exposure modalities, such as particle behavior and deposited dose, likely affect cellular responses. To investigate this, we exposed submerged human bronchial epithelial cells (BEAS-2B) to polystyrene (PS) MNPs vs. aerosol exposure of ALI cultures.

Methods: First, submerged bronchial epithelial cells (BEAS-2B) were exposed to suspensions of PS particles (50 nm or 1 µm) in four different applied concentrations (0.79-50 µg/cm²; 24 h). Second, BEAS-2B cells were cultured at ALI and exposed in a cloud system to PS 1 µm particles (deposited dose: 55.4 µg/cm²; 24 h). Toxicity readouts focused on cytotoxicity (LDH release), inflammation (IL-8 release and transcriptional activation of inflammatory genes), and oxidative stress (DCFH-DA assay, antioxidant gene expression, and assessment of reduced/oxidized glutathione).

Results: In both models, PS exposure did not induce cell death, or an antioxidant response. However, NF-κB transcriptional activity was strongly upregulated in submerged cells in response to both sizes of PS particles in a dose-dependent manner. Gene expression of CXCL1, CXCL2, and CXCL8 increased up to 7-fold after PS microplastic exposure (50 µg/cm²) in the submerged model (which was less pronounced in response to PS nanoplastics) and 2-fold in the ALI model. In contrast, IL-8 secretion increased 1.6-fold for the ALI, but not the submerged model.

Conclusions: Overall, both exposure modalities revealed an inflammatory response toward PS MNPs although with differences, likely due to significant differences in deposited dose.