Resolution of MoS2 nanosheets-induced pulmonary inflammation driven by nanoscale intracellular transformation and extracellular-vesicle shuttles

Pulmonary exposure to some engineered nanomaterials can cause chronic lesions as a result of unresolved inflammation. Among two-dimensional (2D) nanomaterials and graphene, MoS2 have received tremendous attention in optoelectronics and nanomedicine. Here we propose an integrated approach to follow up the transformation of MoS2 nanosheets at the nanoscale and their impact on the lung inflammation status over one month after a single inhalation in mice. Analysis of immune cells, alveolar macrophages, extracellular vesicles, and cytokine profiling in bronchoalveolar lavage fluid (BALF) showed that MoS2 nanosheets induced initiation of lung inflammation that was rapidly resolved despite the persistence of various biotransformed molybdenum-containing nanostructures in alveolar macrophages and extracellular vesicles up to one month. Using in situ liquid phase transmission electron microscopy experiments, we could evidence the dynamics of MoS2 nanosheets transformation triggered by reactive oxygen species. Three main transformation mechanisms were observed directly at the nanoscale level: 1) scrolling of the dispersed sheets leading to the formation of nanoscrolls and folded patches, 2) etching releasing soluble MoO4-, and 3) oxidation generating oxidized sheet fragments. Extracellular vesicles released in BALF were also identified as a potential shuttle of MoS2 nanostructures and their degradation products and more importantly as mediators of inflammation resolution.