Understanding the immunological interactions of engineered nanomaterials: Role of the bio-corona

Engineered nanomaterials are a broad class of materials with the potential for breakthrough applications in many sectors of society not least in medicine. Consequently, safety assessment of nanomaterials and nano-enabled products with respect to human health and the environment is of key importance. To this end, the biological interactions of nanoscale materials must be understood. Here, the dual "identities" of nanomaterials, namely, the material-intrinsic properties or synthetic identity and the acquired, context-dependent properties or biological identity, are discussed in relation to nanomaterial interactions with the immune system, our main defense against foreign intrusion. Specifically, we address whether macrophages and other innate immune cells respond to the synthetic identity or the biological identity of nanomaterials, that is, the surface adsorbed proteins and/or other biomolecules known as the bio-corona, or both? This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Biotransformation of Food-Grade and Nanometric TiO2 in the Oral-Gastro-Intestinal Tract: Driving Forces and Effect on the Toxicity toward Intestinal Epithelial Cells

Background: Oral exposure to titanium dioxide (TiO₂) is common since it is widely used in food and pharmaceutical products. Concern on the safety of this substance has been recently raised, due to the presence of an ultrafine fraction in food-grade TiO₂. Discrepancy exists among data reported in in vitro and in vivo studies on intestinal acute/chronic toxicity of TiO₂. This might be due to the different biological identity of TiO₂ in traditional in vitro test by respect in vivo conditions. Methods: One food-grade TiO₂ and two nanometric TiO₂ samples were treated with a simulated human digestive dystem (SHDS) in order to investigate the bio-transformation occurring to the particles once ingested in term of size distribution (Dynamic Light Scattering—DLS-, Flow Particle Imaging, Asymmetric Flow Field Flow Fractionation-AF4-) and surface modification (Electrophoretic Light Scattering—ELS-, Electron Paramagnetic Resonance Spectroscopy—EPR-). The effect of SHDS on the cyto-, genotoxicity and potential to induce oxidative stress towards human colorectal carcinoma HCT116 cells was also assessed. Results: Aggregation as a consequence of the high ionic strength of the gastric and intestinal simulated fluids was observed, together with the formation of a partially irreversible bio-corona containing phosphate ions and proteins. Such bio-corona led to a partial masking of the TiO₂ particles surface and reactivity. Pristine and treated TiO₂ nanoparticles showed comparable acute toxicity and genotoxicity toward HCT116 cells, whereas a small decrease of the induction of oxidative stress after treatment was observed. Conclusions: Overall the results underline the importance of SHDS as a tool to improve the predictive power of in vitro tests towards intestinal nanomaterial toxicity.

Hide and Seek: Nanomaterial Interactions With the Immune System

Engineered nanomaterials hold promise for a wide range of applications in medicine. However, safe use of nanomaterials requires that interactions with biological systems, not least with the immune system, are understood. Do nanomaterials elicit novel or unexpected effects, or is it possible to predict immune responses to nanomaterials based on how the immune system handles pathogens? How does the bio-corona of adsorbed biomolecules influence subsequent immune interactions of nanomaterials? How does the grafting of polymers such as poly(ethylene glycol) onto nanomaterial surfaces impact on these interactions? Can ancient immune evasion or “stealth” strategies of pathogens inform the design of nanomaterials for biomedical applications? Can nanoparticles co-opt immune cells to target diseased tissues? The answers to these questions may prove useful for the development of nanomedicines.

Lipopolysaccharide Adsorbed to the Bio-Corona of TiO2 Nanoparticles Powerfully Activates Selected Pro-inflammatory Transduction Pathways

It is known that the adsorption of bioactive molecules provides engineered nanoparticles (NPs) with novel biological activities. However, the biological effects of the adsorbed molecules may also be modified by the interaction with NP. Bacterial lipopolysaccharide (LPS), a powerful pro-inflammatory compound, is a common environmental contaminant and is present in several body compartments such as the gut. We recently observed that the co-incubation of LPS with TiO₂ NPs markedly potentiates its pro-inflammatory effects on murine macrophages, suggesting that, when included in a NP bio-corona, LPS activity is enhanced. To distinguish the effects of adsorbed LPS from those of the free endotoxin, a pellet fraction, denominated P25/LPS, was isolated by centrifugation from a mixture of P25 TiO₂ NP (128 µg/ml) and LPS (10 ng/ml) in the presence of fetal bovine serum. Western blot analysis of the pellet eluate indicated that the P25/LPS fraction contained, besides proteins, also LPS, pointing to the presence of LPS-doped NP. The effects of adsorbed or free LPS were then compared in Raw264.7 murine macrophages. RT-PCR was used to evaluate the induction of cytokine genes, whereas active, phosphorylated isoforms of proteins involved in signaling pathways were assessed with western blot. At a nominal LPS concentration of 40 pg/ml, P25/LPS induced the expression of both NF-κB and IRF3-dependent cytokines at levels comparable with those observed with free LPS (10 ng/ml), although with different time courses. Moreover, compared to free LPS, P25/LPS caused a more sustained phosphorylation of p38 MAPK and a more prolonged induction of STAT1-dependent genes. Cytochalasin B partially inhibited the induction of Tnfa by P25/LPS, but not by free LPS, and suppressed the induction of IRF3-dependent genes by either P25/LPS or free LPS. These data suggest that, when included in the bio-corona of TiO₂ NP, LPS exhibits enhanced and time-shifted pro-inflammatory effects. Thus, in assessing the hazard of NP in real life, the enhanced effects of adsorbed bioactive molecules should be taken into account.