Human cell-based in vitro systems to assess respiratory toxicity: a case study using silanes

Inhalation is a major route by which human exposure to substances can occur. Resources have therefore been dedicated to optimize human-relevant in vitro approaches that can accurately and efficiently predict the toxicity of inhaled chemicals for robust risk assessment and management. In this study-the IN vitro Systems to PredIct REspiratory toxicity Initiative-2 cell-based systems were used to predict the ability of chemicals to cause portal-of-entry effects on the human respiratory tract. A human bronchial epithelial cell line (BEAS-2B) and a reconstructed human tissue model (MucilAir, Epithelix) were exposed to triethoxysilane (TES) and trimethoxysilane (TMS) as vapor (mixed with N2 gas) at the air-liquid interface. Cell viability, cytotoxicity, and secretion of inflammatory markers were assessed in both cell systems and, for MucilAir tissues, morphology, barrier integrity, cilia beating frequency, and recovery after 7 days were also examined. The results show that both cell systems provide valuable information; the BEAS-2B cells were more sensitive in terms of cell viability and inflammatory markers, whereas MucilAir tissues allowed for the assessment of additional cellular effects and time points. As a proof of concept, the data were also used to calculate human equivalent concentrations. As expected, based on chemical properties and existing data, the silanes demonstrated toxicity in both systems with TMS being generally more toxic than TES. Overall, the results demonstrate that these in vitro test systems can provide valuable information relevant to predicting the likelihood of toxicity following inhalation exposure to chemicals in humans.

An evaluation of reproductive toxicity studies and data interpretation of N-methylpyrrolidone for risk assessment: An expert panel review

An expert panel was assembled to evaluate reproductive toxicology study data and their application to health risk assessment to provide input on the data quality, interpretation, and application of data from three multi-generation reproductive toxicity studies of N-methylpyrrolidone (NMP). Panelists were engaged using a double-blinded, modified Delphi format that consisted of three rounds. Key studies were scored using the U.S. Environmental Protection Agency's (EPA) questions and general considerations to guide the evaluation of experimental animal studies for systematic review. The primary conclusions of the panel are that one of the studies (Exxon, 1991) is not a high-quality study due to several design flaws that includes: (1) exceedance of the maximum tolerable dose in the high dose group; (2) failure to adjust feed concentrations of NMP during the lactation period, resulting in NMP doses that were 2- to 3-fold higher than nominal levels; and/or (3) underlying reproductive performance problems in the strain of rats used. For these reasons, the panel recommended that this study should not be considered for quantitative risk assessment of NMP. Exclusion of this study, and its corresponding data for male fertility and female fecundity, from the quantitative risk assessment results in a change in the identification of the most sensitive endpoint. Instead, changes in rat fetal/pup body weight, an endpoint previously selected by EPA, was identified as an appropriate basis for human health risk assessment based on a consideration of the best available science and weight of scientific evidence supported by the NMP toxicity database.

Use of new approach methodologies (NAMs) to meet regulatory requirements for the assessment of tobacco and other nicotine-containing products

Regulatory frameworks on tobacco and other nicotine-containing products (TNCP) continue to evolve as novel products emerge, including electronic nicotine delivery systems (e.g., electronic cigarettes or vaping products), heated tobacco products, or certain smokeless products (e.g., nicotine pouches). This article focuses on selected regulations for TNCPs that do not make health claims, and on the opportunities to use new approach methodologies (NAMs) to meet regulatory requirements for toxicological information. The manuscript presents a brief overview of regulations and examples of feedback from regulatory agencies whilst highlighting NAMs that have been successfully applied, or could be used, in a regulatory setting, either as stand-alone methods or as part of a weight-of-evidence approach to address selected endpoints. The authors highlight the need for agencies and stakeholders to collaborate and communicate on the development and application of NAMs to address specific regulatory toxicological endpoints. Collaboration across sectors and geographies will facilitate harmonized use of robust testing approaches to evaluate TNCPs without animal testing.

Use of new approach methodologies (NAMs) to meet regulatory requirements for the assessment of industrial chemicals and pesticides for effects on human health

New approach methodologies (NAMs) are increasingly being used for regulatory decision making by agencies worldwide because of their potential to reliably and efficiently produce information that is fit for purpose while reducing animal use. This article summarizes the ability to use NAMs for the assessment of human health effects of industrial chemicals and pesticides within the United States, Canada, and European Union regulatory frameworks. While all regulations include some flexibility to allow for the use of NAMs, the implementation of this flexibility varies across product type and regulatory scheme. This article provides an overview of various agencies’ guidelines and strategic plans on the use of NAMs, and specific examples of the successful application of NAMs to meet regulatory requirements. It also summarizes intra- and inter-agency collaborations that strengthen scientific, regulatory, and public confidence in NAMs, thereby fostering their global use as reliable and relevant tools for toxicological evaluations. Ultimately, understanding the current regulatory landscape helps inform the scientific community on the steps needed to further advance timely uptake of approaches that best protect human health and the environment.

Effects of diethylmaleate on DNA damage and repair in the mouse brain

The enzyme 8-oxoguanine DNA glycosylase 1 participates in the repair of damaged DNA by excising the oxidized base 8-hydroxy-2'-deoxyguanosine. We have previously demonstrated that enzymatic activity of this enzyme is inversely related to the levels of the damaged base in specific brain regions. We now report that the activity of 8-oxoguanine DNA glycosylase 1 is increased in a region-specific manner following treatment with diethylmaleate, a compound that reduces glutathione levels in the cell. A single treatment with diethylmaleate elicited a significant increase ( approximately 2-fold) in the activity of 8-oxoguanine DNA glycosylase 1 in three brain regions with low basal levels of activity (cerebellum, cortex, and pons/medulla). There was no change in the activity of 8-oxoguanine DNA glycosylase 1 in those regions with high basal levels of activity (hippocampus, caudate/putamen, and midbrain). This is the first report to demonstrate that DNA repair capacity can be upregulated in the CNS, and the increased repair activity correlates with a reduction in the levels of DNA damage. The brain region-specific capacity to deal with increased oxidative damage to DNA may be responsible, in part, for the vulnerability of specific neuronal populations with aging, sources of oxidative stress, and neurodegenerative diseases.