New insight into artifactual phenomena during in vitro toxicity assessment of engineered nanoparticles: Study of TNF-α adsorption on alumina oxide nanoparticle

Establishing relationships between particle-induced in vitro and in vivo inflammation endpoints to better extrapolate between in vitro markers and in vivo fibrosis

BACKGROUND

Toxicity assessment for regulatory purposes is starting to move away from traditional in vivo methods and towards new approach methodologies (NAM) such as high-throughput in vitro models and computational tools. For materials with limited hazard information, utilising quantitative Adverse Outcome Pathways (AOPs) in a testing strategy involving NAM can produce information relevant for risk assessment. The aim of this work was to determine the feasibility of linking in vitro endpoints to in vivo events, and moreover to key events associated with the onset of a chosen adverse outcome to aid in the development of NAM testing strategies. To do this, we focussed on the adverse outcome pathway (AOP) relating to the onset of pulmonary fibrosis.

RESULTS

We extracted in vivo and in vitro dose-response information for particles known to induce this pulmonary fibrosis (crystalline silica, specifically α-quartz). To test the in vivo-in vitro extrapolation (IVIVE) determined for crystalline silica, cerium dioxide nanoparticles (nano-CeO₂) were used as a case study allowing us to evaluate our findings with a less studied substance. The IVIVE methodology outlined in this paper is formed of five steps, which can be more generally summarised into two categories (i) aligning the in vivo and in vitro dosimetry, (ii) comparing the dose-response curves and derivation of conversion factors.

CONCLUSION

Our analysis shows promising results with regards to correlation of in vitro cytokine secretion to in vivo acute pulmonary inflammation assessed by polymorphonuclear leukocyte influx, most notable is the potential of using IL-6 and IL-1β cytokine secretion from simple in vitro submerged models as a screening tool to assess the likelihood of lung inflammation at an early stage in product development, hence allowing a more targeted investigation using either a smaller, more targeted in vivo study or in the future a more complex in vitro protocol. This paper also highlights the strengths and limitations as well as the current difficulties in performing IVIVE assessment and suggestions for overcoming these issues.

Experimental and Computational Nanotoxicology-Complementary Approaches for Nanomaterial Hazard Assessment

The growing development and applications of nanomaterials lead to an increasing release of these materials in the environment. The adverse effects they may elicit on ecosystems or human health are not always fully characterized. Such potential toxicity must be carefully assessed with the underlying mechanisms elucidated. To that purpose, different approaches can be used. First, experimental toxicology consisting of conducting in vitro or in vivo experiments (including clinical studies) can be used to evaluate the nanomaterial hazard. It can rely on variable models (more or less complex), allowing the investigation of different biological endpoints. The respective advantages and limitations of in vitro and in vivo models are discussed as well as some issues associated with experimental nanotoxicology. Perspectives of future developments in the field are also proposed. Second, computational nanotoxicology, i.e., in silico approaches, can be used to predict nanomaterial toxicity. In this context, we describe the general principles, advantages, and limitations especially of quantitative structure–activity relationship (QSAR) models and grouping/read-across approaches. The aim of this review is to provide an overview of these different approaches based on examples and highlight their complementarity.

Graphene oxide incorporating carbon fibre-reinforced composites submitted to simultaneous impact and fire: Physicochemical characterisation and toxicology of the by-products

The toxicological profile of particulates released from carbon fibre-reinforced composites (CFC) incorporating nanoadditives, under impact and fire conditions (e.g. aircraft crash), is unknown to date. Our aim was to investigate the effects of simultaneous impact and fire on the physicochemical features of the particles released from CFCs produced from a graphene oxide (GO)-reinforced epoxy resin and the consequences on its toxicological profile. CFC samples with (CFC + GO) or without GO (CFC) were subjected to simultaneous impact and fire through a specific setup. Soot and residues were characterised and their toxicity was compared to that of virgin GO. Virgin GO was not cytotoxic but induced pro-inflammatory and oxidative stress responses. The toxicity profile of CFC was similar for soot and residue: globally not cytotoxic, inducing a pro-inflammatory response and no oxidative stress. However, an increased cytotoxicity at the highest concentration was potentially caused by fibres of reduced diameters or fibril bundles, which were observed only in this condition. While the presence of GO in CFC did not alter the cytotoxicity profile, it seemed to drive the pro-inflammatory and oxidative stress response in soot. On the contrary, in CFC + GO residue the biological activity was decreased due to the physicochemical alterations of the materials.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.

Interaction of biologically relevant proteins with ZnO nanomaterials: A confounding factor for in vitro toxicity endpoints

The results of in vitro toxicological studies for manufactured nanomaterials (MNs) are often contradictory and not reproducible. Interference of the MNs with assays has been suggested. However, understanding for which materials and how these artefacts occur remains a major challenge. This study investigated interactions between two well-characterized ZnO MNs (NM-110 and NM-111) and lactate dehydrogenase (LDH), and two interleukins (IL-6 and IL-8). Particles (10 to 640 μg/mL) and proteins were incubated for up to 24 h in routine in vitro assays test conditions. LDH activity (OD_LDH), but not interleukins concentrations, decreased sharply in a dose-dependent manner within an hour after exposure (OD_LDH < 60% of OD_ref for both MNs at 10 μg/mL). A Freundlich adsorption isotherm was successfully applied, indicating multilayer adsorption of LDH. ZnO MNs and LDH had neutral to slightly negative surface charges in dispersion, precluding electrostatic attachment. Particle sedimentation was not a limiting factor. Fast dissolution of ZnO MNs was shown and Zn²⁺ could play a role in the OD_LDH drop. To summarize, ZnO MNs quickly reduced OD_LDH due to concentration-dependent adsorption and LDH inhibition by interaction with dissolved Zn. The control of particle interference in toxicological in vitro assays should become mandatory to avoid misleading interpretation of results.

Biodistribution and toxicity of spherical aluminum oxide nanoparticles

With the rapid development of the nano-industry, concerns about their potential adverse health effects have been raised. Thus, ranking accurately their toxicity and prioritizing for in vivo testing through in vitro toxicity test is needed. In this study, we used three types of synthesized aluminum oxide nanoparticles (AlONPs): γ-aluminum oxide hydroxide nanoparticles (γ-AlOHNPs), γ- and α-AlONPs. All three AlONPs were spherical, and the surface area was the greatest for γ-AlONPs, followed by the α-AlONPs and γ-AlOHNPs. In mice, γ-AlOHNPs accumulated the most 24 h after a single oral dose. Additionally, the decreased number of white blood cells (WBC), the increased ratio of neutrophils and the enhanced secretion of interleukin (IL)-8 were observed in the blood of mice dosed with γ-AlOHNPs (10 mg kg(-1)). We also compared their toxicity using four different in vitro test methods using six cell lines, which were derived from their potential target organs, BEAS-2B (lung), Chang (liver), HACAT (skin), H9C2 (heart), T98G (brain) and HEK-293 (kidney). The results showed γ-AlOHNPs induced the greatest toxicity. Moreover, separation of particles was observed in a transmission electron microscope (TEM) image of cells treated with γ-AlOHNPs, but not γ-AlONPs or α-AlONPs. In conclusion, our results suggest that the accumulation and toxicity of AlONPs are stronger in γ-AlOHNPs compared with γ-AlONPs and α-AlONPs owing their low stability within biological system, and the presence of hydroxyl group may be an important factor in determining the distribution and toxicity of spherical AlONPs.

Adsorption of lactate dehydrogenase enzyme on carbon nanotubes: how to get accurate results for the cytotoxicity of these nanomaterials

Carbon nanotube (CNT) cytotoxicity is frequently investigated using in vitro classical toxicology assays. However, these cellular tests, usually based on the use of colorimetric or fluorimetric dyes, were designed for chemicals and may not be suitable for nanosized materials. Indeed, because of their unique physicochemical properties CNT can interfere with the assays and bias the results. To get accurate data and draw reliable conclusions, these artifacts should be carefully taken into account. The aim of this study was to evaluate qualitatively and quantitatively the interferences occurring between CNT and the commonly used lactate dehydrogenase (LDH) assay. Experiments under cell-free conditions were performed, and it was clearly demonstrated that artifacts occurred. They were due to the intrinsic absorbance of CNT on one hand and the adsorption of LDH at the CNT surface on the other hand. The adsorption of LDH on CNT was modeled and was found to fit the Langmuir model. The K(ads) and n(eq) constants were defined, allowing the correction of results obtained from cellular experiments to get more accurate data and lead to proper conclusions on the cytotoxicity of CNT.