Graphene oxide is degraded by neutrophils and the degradation products are non-genotoxic.

Neutrophils were previously shown to digest oxidized carbon nanotubes through a myeloperoxidase (MPO)-dependent mechanism, and graphene oxide (GO) was found to undergo degradation when incubated with purified MPO, but there are no studies to date showing degradation of GO by neutrophils. Here we produced endotoxin-free GO by a modified Hummers' method and asked whether primary human neutrophils stimulated to produce neutrophil extracellular traps or activated to undergo degranulation are capable of digesting GO. Biodegradation was assessed using a range of techniques including Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and mass spectrometry. GO sheets of differing lateral dimensions were effectively degraded by neutrophils. As the degradation products could have toxicological implications, we also evaluated the impact of degraded GO on the bronchial epithelial cell line BEAS-2B. MPO-degraded GO was found to be non-cytotoxic and did not elicit any DNA damage. Taken together, these studies have shown that neutrophils can digest GO and that the biodegraded GO is non-toxic for human lung cells.

Fibrillar vs crystalline nanocellulose pulmonary epithelial cell responses: Cytotoxicity or inflammation?

Nanocellulose (NC) is emerging as a highly promising nanomaterial for a wide range of applications. Moreover, many types of NC are produced, each exhibiting a slightly different shape, size, and chemistry. The main objective of this study was to compare cytotoxic effects of cellulose nanocrystals (CNC) and nanofibrillated cellulose (NCF). The human lung epithelial cells (A549) were exposed for 24 h and 72 h to five different NC particles to determine how variations in properties contribute to cellular outcomes, including cytotoxicity, oxidative stress, and cytokine secretion. Our results showed that NCF were more toxic compared to CNC particles with respect to cytotoxicity and oxidative stress responses. However, exposure to CNC caused an inflammatory response with significantly elevated inflammatory cytokines/chemokines compared to NCF. Interestingly, cellulose staining indicated that CNC particles, but not NCF, were taken up by the cells. Furthermore, clustering analysis of the inflammatory cytokines revealed a similarity of NCF to the carbon nanofibers response and CNC to the chitin, a known immune modulator and innate cell activator. Taken together, the present study has revealed distinct differences between fibrillar and crystalline nanocellulose and demonstrated that physicochemical properties of NC are critical in determining their toxicity.