There is an increasing need for new approach methodologies (NAMs) for safety assessment of nanomaterials (NMs) in order to keep pace with innovation. In vitro assays are useful tools during pre-market hazard screening approaches of NMs to prioritize safe(r) candidate NMs and reduce the amount of regulatory testing required. For pre-regulatory hazard screening applications, it is crucial that in vitro assays have the capacity to distinguish between NMs based on their hazard potency and have the ability to provide accurate hazard rankings. In this paper, four types of silica particles (crystalline, pyrogenic, colloidal, and silane functionalized colloidal) were subjected to twenty-four in vitro assays to obtain hazard rankings using dose–response modelling. The assays were chosen for their relevance in the mechanism of action towards pulmonary inflammation upon inhalation of silica particles. The hazard rankings of silica particles were affected by cell type (alveolar or bronchial epithelial cells, macrophages), read-out method (cell viability, release of pro-inflammatory mediators, reactive oxygen species), and exposure method (submerged, air–liquid interface), complicating the assessment of the actual human hazard. Of particular note was an often muted in vitro response to the crystalline silica used in this study (DQ12), when in vivo data ranked this material as high hazard, due to the chronic and persistent in vivo inflammatory response to crystalline silica, highlighting an important functional discord between these models. However, the potency ranking of the silica particles to induce secretion of the pro-inflammatory mediator IL-1β by THP-1 cells differentiated to M0 macrophages as well as red blood cell haemolysis corresponded more closely to the hazard ranking based on data from rat inhalation studies. These assays should be further explored as indicators for human hazard potential of silica particles and other particles following a similar mechanism of action.

This article presents experimental evidence and computed molecular models of a potential interaction between receptor domain D5 of TrkB with the carboxyl-terminal domain of tetanus neurotoxin (Hc-TeNT). Computational simulations of a novel small cyclic oligopeptide are designed, synthesized, and tested for possible tetanus neurotoxin-D5 interaction. A hot spot of this protein-protein interaction is identified in analogy to the hitherto known crystal structures of the complex between neurotrophin and D5. Hc-TeNT activates the neurotrophin receptors, as well as its downstream signaling pathways, inducing neuroprotection in different stress cellular models. Based on these premises, we propose the Trk receptor family as potential proteic affinity receptors for TeNT. In vitro, Hc-TeNT binds to a synthetic TrkB-derived peptide and acts similar to an agonist ligand for TrkB, resulting in phosphorylation of the receptor. These properties are weakened by the mutagenesis of three residues of the predicted interaction region in Hc-TeNT. It also competes with Brain-derived neurotrophic factor, a native binder to human TrkB, for the binding to neural membranes, and for uptake in TrkB-positive vesicles. In addition, both molecules are located together in vivo at neuromuscular junctions and in motor neurons.