Lung Persistence, Biodegradation, and Elimination of Graphene‐Based Materials are Predominantly Size‐Dependent and Mediated by Alveolar Phagocytes

Abstract

Graphene‐based materials (GBMs) have promising applications in various sectors, including pulmonary nanomedicine. Nevertheless, the influence of GBM physicochemical characteristics on their fate and impact in lung has not been thoroughly addressed. To fill this gap, the biological response, distribution, and bio‐persistence of four different GBMs in mouse lungs up to 28 days after single oropharyngeal aspiration are investigated. None of the GBMs, varying in size (large versus small) and carbon to oxygen ratio as well as thickness (few‐layers graphene (FLG) versus thin graphene oxide (GO)), induce a strong pulmonary immune response. However, recruited neutrophils internalize nanosheets better and degrade GBMs faster than macrophages, revealing their crucial role in the elimination of small GBMs. In contrast, large GO sheets induce more damages due to a hindered degradation and long‐term persistence in macrophages. Overall, small dimensions appear to be a leading feature in the design of safe GBM pulmonary nanovectors due to an enhanced degradation in phagocytes and a faster clearance from the lungs for small GBMs. Thickness also plays an important role, since decreased material loading in alveolar phagocytes and faster elimination are found for FLGs compared to thinner GOs. These results are important for designing safer‐by‐design GBMs for biomedical application.

Pulmonary Toxicity of Boron Nitride Nanomaterials Is Aspect Ratio Dependent

“…Overall, the striking contrast between high aspect ratio BNNTs and low aspect ratio h-BN effects highlights their main physical difference, i.e., their dimensional aspect ratio, as the leading cause of their toxicity, in a similar fashion to what was reported before for carbon-based materials when comparing long and rigid carbon nanotubes with small dimension graphene nanoplatelets or GO. 26,27,35 In a comparable study to ours, Xin et al reported acute and chronic adverse effects after pharyngeal aspiration to 40 μg of BNNTs. 11 In line with our findings, they found an influx in neutrophils and eosinophils as well as the presence of lymphocytes in BALF.…”

“…Overall, the striking contrast between high aspect ratio BNNTs and low aspect ratio h -BN effects highlights their main physical difference, i.e. , their dimensional aspect ratio, as the leading cause of their toxicity, in a similar fashion to what was reported before for carbon-based materials when comparing long and rigid carbon nanotubes with small dimension graphene nanoplatelets or GO. ,, …”

“…Altogether, the evidence of chronic inflammation and activation of adaptive immunity for BNNTs suggests that long-term damage may arise in the lungs and other organs, as previously shown after exposure to other high aspect ratio materials, such as MWCNTs. 20,26,35,36 The consistent activation of SAA3 after a single exposure, a biomarker often linked to the risk of cardiovascular diseases, 37,38 further stresses the need to study the impact of repeated exposure to BNNTs beyond the lungs and in particular on the cardiovascular system. Nanotubes but Not 2D Nanosheets Caused Lung Tissue Damage.…”

“…The absence of acute immune response was somewhat surprising because most of the 2D materials tested so far by us and others induced at least an acute lung inflammation after administration to high doses in rodents. 35,39,40 In several studies, single pharyngeal aspiration of graphene nanoplatelets (GNPs) or few-layer graphene (FLGs) caused acute lung inflammation that resolved by day 7 or 28. 39,41−44 Importantly, in most of these studies, the authors did not observe chronic inflammation or tissue damage, although some of these materials were shown to persist in the respiratory tract for a long period.…”

“…[25][26][27]35,39,50,51 In our previous work, the size-dependent differences were ascribed to impaired degradation of micrometric GO sheets in alveolar macrophages compared to nanometric GO sheets, which combined with a reduced clearance of the micrometric materials from the alveolar region led to their biopersistence in the lungs, and therefore a more adverse impact. 35 Additionally, in a recent study specifically designed to evaluate the chronic immune response and impact after multiple challenges with GO sheets, we revealed that the absence of an adaptive immunity activation by GO with small lateral dimensions was a good prognosis of GBM lung biocompatibility and could explain the efficient recovery and absence of tissue damage. 26,27 Herein, it could therefore be inferred that h-BN nanosheets did not cause inflammation not only because of their elimination from the airways but also because of their small lateral dimensions, which together with their relatively small thickness provide them with low aspect ratio physical characteristics.…”