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The WST-1 assay is the most common test to assess the in vitro cytotoxicity of chemicals. Tetrazolium-based assays can, however, be affected by the interference of tested chemicals, including carbon nanotubes or Mg particles. Here, we report a new interference of Mn materials with the WST-1 assay. Endothelial cells exposed to Mn particles (Mn alone or Fe-Mn alloy from 50 to 1600 μg/ml) were severely damaged according to the WST-1 assay, but not the ATP content assay. Subsequent experiments revealed that Mn particles interfere with the reduction of the tetrazolium salt to formazan. Therefore, the WST-1 assay is not suitable to evaluate the in vitro cytotoxicity of Mn-containing materials, and luminescencebased assays such as CellTiter-Glo ® appear more appropriate.

Fe-based materials have increasingly been considered for the development of biodegradable cardiovascular stents. A wide range of in vitro and in vivo studies should be done to fully evaluate their biocompatibility. In this review, we summarized and analyzed the findings and the methodologies used to assess the biocompatibility of Fe materials. The majority of investigators drew conclusions about in vitro Fe toxicity based on indirect contact results. The setup applied in these tests seems to overlook the possible effects of Fe corrosion and does not allow for understanding of the complexity of released chemical forms and their possible impact on tissue. It is in particular important to ensure that test setups or interpretations of in vitro results do not hide some important mechanisms, leading to inappropriate subsequent in vivo experiments. On the other hand, the sample size of existing in vivo implantations is often limited, and effects such as local toxicity or endothelial function are not deeply scrutinized. The main advantages and limitations of in vitro design strategies applied in the development of Fe-based alloys and the correlation with in vivo studies are discussed. It is evident from this literature review that we are not yet ready to define an Fe-based material as safe or biocompatible.

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A growing number of epidemiological studies has linked exposure to traffic-related air pollution (TRAP) to neurological and neurodegenerative diseases. In a previous study, we showed that subchronic inhalation exposure to diesel engine exhaust, as a model of TRAP, aggravates amyloid-β plaque formation and motor function impairment in the 5xFAD transgenic mouse model of Alzheimer’s disease (AD). To further strengthen the epidemiological association between TRAP and AD we exposed 5xFAD and wildtype littermate mice for 5 h/day, 5 days/week during 2 or 4 consecutive weeks at a representative urban traffic-dominated location to: (I) concentrated ambient particles, (II) particle filtered ambient air or (III) clean air (control).  Our study revealed that repeated inhalation exposure to TRAP accelerates plaque formation in the 5xFAD mice. Data also indicated that the gaseous fraction of the air pollutant mixture probably plays only a minor role in this effect. The major outcome of this study substantiates the role of air pollution in AD and suggests that long-term exposure to traffic-related air pollution particles is a risk factor for this debilitating disease. Acknowledgements: The work leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 814978 (TUBE) and a cross-border grant awarded by the Alzheimer Forschung Initiative (AFI, Germany) and Alzheimer Nederland.

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