Role of engineered metal oxide nanoparticle agglomeration in reactive oxygen species generation and cathepsin B release in NLRP3 inflammasome activation and pulmonary toxicity

Abstract

Incomplete understanding of the contributions of dispersants and engineered nanoparticles/materials (ENM) agglomeration state to biological outcomes presents an obstacle for toxicological studies. Although reactive oxygen species (ROS) production is often regarded as the primary indicator of ENM bioactivity and toxicity, it remains unclear whether ENM produce ROS or whether ROS is an outcome of ENM-induced cell injury. Phagolysosomal disruption and cathepsin B release also promote bioactivity through inflammasome activation. Therefore, specific particle parameters, i.e. preexposure dispersion status and particle surface area, of two ENM (NiO and CeO₂) were used to evaluate the role of ROS generation and cathepsin B release during ENM-induced toxicity. Male C57BL/6J mice were exposed to 0, 20, 40, or 80 μg of poorly or well-dispersed NiO-NP or CeO₂-NP in four types of dispersion media. At 1- and 7-day postexposure, lung lavage fluid was collected to assess inflammation, cytotoxicity, and inflammasome activation. Results showed that preexposure dispersion status correlated with postexposure pulmonary bioactivity. The differences in bioactivity of NiO-NP and CeO₂-NP are likely due to NiO-NP facilitating the release of cathepsin B and in turn inflammasome activation generating proinflammatory cytokines. Further, both metal oxides acted as free radical scavengers. Depending on the pH, CeO₂-NP acted as a free radical scavenger in an acidic environment (an environment mimicking the lysosome) while the NiO-NP acted as a scavenger in a physiological pH (an environment that mimics the cytosol of the cell). Therefore, results from this study suggest that ENM-induced ROS is not likely a mechanism of inflammasome activation.

Keywords:

• activation
• agglomeration
• cytotoxicity
• engineered nanoparticles
• inflammasome
• inflammation
• pulmonary toxicity
• ROS

Acknowledgements

The authors would like to thank Diane Schwegler-Berry for her assistance on obtaining the TEM and SEM images presented in the MS. Mention of brand name does not constitute product endorsement. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

Declaration of interest

The authors declare that they have no competing interests.

This work was supported by NIH [grant No. F32 ES021341].