Translating nanoparticle dosimetry from conventional in vitro systems to occupational inhalation exposures

Overview of in vitro-in vivo extrapolation approaches for the risk assessment of nanomaterial toxicity

Nanomaterials are increasingly used in many applications due to their enhanced properties. To ensure their safety for humans and the environment, nanomaterials need to be evaluated for their potential risk. The risk assessment analysis on the nanomaterials based on animal or in vivo studies is accompanied by several concerns, including animal welfare, time and cost needed for the studies. Therefore, incorporating in vitro studies in the risk assessment process is increasingly considered. To be able to analyze the potential risk of nanomaterial to human health, there are factors to take into account. Utilizing in vitro data in the risk assessment analysis requires methods that can be used to translate in vitro data to predict in vivo phenomena (in vitro-in vivo extrapolation (IVIVE) methods) to be incorporated, to obtain a more accurate result. Apart from the experiments and species conversion (for example, translation between the cell culture, animal and human), the challenge also includes the unique properties of nanomaterials that might cause them to behave differently compared to the same materials in a bulk form. This overview presents the IVIVE techniques that are developed to extrapolate pharmacokinetics data or doses. A brief example of the IVIVE methods for chemicals is provided, followed by a more detailed summary of available IVIVE methods applied to nanomaterials. The IVIVE techniques discussed include the comparison between in vitro and in vivo studies, methods to rene the dose metric or the in vitro models, allometric approach, mechanistic modeling, Multiple-Path Particle Dosimetry (MPPD), methods using organ burden data and also approaches that are currently being developed.

Disruption of phosphofructokinase activity and aerobic glycolysis in human bronchial epithelial cells by atmospheric ultrafine particulate matter

Exposure to ambient ultrafine particulate matter (UPM) causes respiratory disorders; however, the underlying molecular mechanisms remain unclear. In this study, we synthesized simulated UPM (sUPM) with controlled physicochemical properties using the spark-discharge method. Subsequently, we investigated the biological effects of sUPM using BEAS-2B human bronchial epithelial cells (HBECs) and a mouse intratracheal instillation model. High throughput RNA-sequencing and bioinformatics analyses revealed that dysregulation of the glycolytic metabolism is involved in the inhibited proliferation and survival of HBECs by sUPM treatment. Furthermore, signaling pathway and enzymatic analyses showed that the treatment of BEAS-2B cells with sUPM induces the inactivation of extracellular signal-regulated kinase (ERK) and protein kinase B (PKB, also known as AKT), resulting in the downregulation of phosphofructokinase 2 (PFK2) S483 phosphorylation, PFK enzyme activity, and aerobic glycolysis in HBECs in an oxidative stress-independent manner. Additionally, intratracheal instillation of sUPM reduced the phosphorylation of ERK, AKT, and PFK2, decreased proliferation, and increased the apoptosis of bronchial epithelial cells in mice. The findings of this study imply that UPM induces pulmonary toxicity by disrupting aerobic glycolytic metabolism in lung epithelial cells, which can provide novel insights into the toxicity mechanisms of UPM and strategies to prevent their toxic effects.

Modelled lung deposition and retention of welding fume particles in occupational scenarios: a comparison to doses used in vitro

Translating particle dose from in vitro systems to relevant human exposure remains a major challenge for the use of in vitro studies in assessing occupational hazard and risk of particle exposure. This study aimed to model the lung deposition and retention of welding fume particles following occupational scenarios and subsequently compare the lung doses to those used in vitro. We reviewed published welding fume concentrations and size distributions to identify input values simulating real-life exposure scenarios in the multiple path particle dosimetry (MPPD) model. The majority of the particles were reported to be below 0.1 μm and mass concentrations ranged between 0.05 and 45 mg/m³. Following 6-h exposure to 5 mg/m³ with a count median diameter of 50 nm, the tracheobronchial lung dose (0.89 µg/cm²) was found to exceed the in vitro cytotoxic cell dose (0.125 µg/cm²) previously assessed by us in human bronchial epithelial cells (HBEC-3kt). However, the tracheobronchial retention decreased rapidly when no exposure occurred, in contrast to the alveolar retention which builds-up over time and exceeded the in vitro cytotoxic cell dose after 1.5 working week. After 1 year, the tracheobronchial and alveolar retention was estimated to be 1.15 and 2.85 µg/cm², respectively. Exposure to low-end aerosol concentrations resulted in alveolar retention comparable to cytotoxic in vitro dose in HBEC-3kt after 15-20 years of welding. This study demonstrates the potential of combining real-life exposure data with particle deposition modelling to improve the understanding of in vitro concentrations in the context of human occupational exposure.

Combined in vitro-in vivo dosimetry enables the extrapolation of in vitro doses to human exposure levels: A proof of concept based on a meta-analysis of in vitro and in vivo titanium dioxide toxicity data

Evaluating the potential risks of nanomaterials on human health is fundamental to assure their safety. To do so, Human Health Risk Assessment (HHRA) relies mostly on animal studies to provide information about nanomaterials toxicity. The scarcity of such data, due to the shift of the nanotoxicology field away from a phenomenological, animal-based approach and towards a mechanistic understanding based on in vitro studies, represents a challenge for HHRA. Implementing in vitro data in the HHRA methodology requires an extrapolation strategy; combining in vitro dosimetry and lung dosimetry can be an option to estimate the toxic effects on lung cells caused by inhaled nanomaterials. Since the two dosimetry models have rarely been used together, we developed a combined dosimetry model (CoDo) that estimates the air concentrations corresponding to the in vitro doses, extrapolating in this way in vitro doses to human doses. Applying the model to a data set of in vitro and in vivo toxicity data about titanium dioxide, we demonstrated CoDo's multiple applications. First, we confirmed that most in vitro doses are much higher than realistic human exposures, considering the Swiss Occupational Exposure Limit as benchmark. The comparison of the Benchmark Doses (BMD) extrapolated from in vitro and in vivo data, using the surface area dose metric, showed that despite both types of data had a quite wide range, animal data were overall more precise. The high variability of the results may be due both to the dis-homogeneity of the original data (different cell lines, particle properties, etc.) and to the high level of uncertainty in the extrapolation procedure caused by both model assumptions and experimental conditions. Moreover, while the surface area BMDs from studies on rodents and rodent cells were comparable, human co-cultures showed less susceptibility and had higher BMDs regardless of the titanium dioxide type. Last, a Support Vector Machine classification model built on the in vitro data set was able to predict the BMD-derived human exposure level range for viability effects based on the particle properties and experimental conditions with an accuracy of 85%, while for cytokine release in vitro and neutrophil influx in vivo the model had a lower performance.