Alternative approaches for acute inhalation toxicity testing to address global regulatory and non-regulatory data requirements: An international workshop report

Abstract

Inhalation toxicity testing, which provides the basis for hazard labeling and risk management of chemicals with potential exposure to the respiratory tract, has traditionally been conducted using animals. Significant research efforts have been directed at the development of mechanistically based, non-animal testing approaches that hold promise to provide human-relevant data and an enhanced understanding of toxicity mechanisms. A September 2016 workshop, "Alternative Approaches for Acute Inhalation Toxicity Testing to Address Global Regulatory and Non-Regulatory Data Requirements", explored current testing requirements and ongoing efforts to achieve global regulatory acceptance for non-animal testing approaches. The importance of using integrated approaches that combine existing data with in vitro and/or computational approaches to generate new data was discussed. Approaches were also proposed to develop a strategy for identifying and overcoming obstacles to replacing animal tests. Attendees noted the importance of dosimetry considerations and of understanding mechanisms of acute toxicity, which could be facilitated by the development of adverse outcome pathways. Recommendations were made to (1) develop a database of existing acute inhalation toxicity data; (2) prepare a state-of-the-science review of dosimetry determinants, mechanisms of toxicity, and existing approaches to assess acute inhalation toxicity; (3) identify and optimize in silico models; and (4) develop a decision tree/testing strategy, considering physicochemical properties and dosimetry, and conduct proof-of-concept testing. Working groups have been established to implement these recommendations.

New Approach Methods to Evaluate Health Risks of Air Pollutants: Critical Design Considerations for In Vitro Exposure Testing

“…This is particularly important for air pollutant research, as many airborne chemicals and mixtures are currently lacking data required for hazard assessment. A few reviews have been published previously on the topic of in vitro models in inhalation toxicology [45,46], including some that were recently published [47,48]. Here, we contribute to this expanding body of literature by reviewing critical elements of study design to incorporate when planning and executing in vitro methods in air pollution research, with the ultimate goal of incorporating these NAMs into chemical hazard and risk assessment applications.…”

“…This method becomes problematic when the testing of insoluble chemicals is needed, as well as airborne particulates and complex mixtures that vary in composition once dissolved in a liquid. Furthermore, the apical media inherently in submerged cell cultures can alter the respiratory epithelial cell phenotype, expression of critical genes, and barrier conditions for gases to contact the cells under evaluation [48]. Although cell-based assays using submerged conditions can still impart useful information surrounding air pollution toxicity, these limitations must be taken into account when designing and interpreting such studies.…”

“…If the main route of exposure in humans is via inhalation for the particular chemical or particle of interest, then it is clearly advantageous to evaluate exposure effects in a similar fashion. It has become widely accepted that exposing cells at the ALI is advantageous to simulate an inhalation exposure [47,48]. Cells in the ALI condition are cultured on porous inserts that contain cell culture medium in the basolateral side to maintain viable cells, while the apical side is directly exposed to the air, permitting a direct exposure [88,89].…”

Nonanimal Approaches to Assessing the Toxicity of Inhaled Substances: Current Progress and Future Promise

“…An excellent example of such a collaborative effort was a 2016 meeting, organized by the NTP Interagency Center for the Evaluation of Alternative Toxicology Methods and the PETA International Science Consortium Ltd., which was summarized in the publication ''Alternative approaches for acute inhalation toxicity testing to address global regulatory and non-regulatory data requirements: An international workshop report.'' 5 The workshop was organized in response to interest in the development, validation, and implementation of effective and efficient approaches that replace animal use for acute inhalation toxicity testing, and was attended by about 50 scientists from regulatory agencies, academia, nongovernmental organizations (NGOs), and industry. The product of this workshop was a strategy to optimize these approaches, with four primary recommendations on how to execute this strategy.…”

Prevalidation of an Acute Inhalation Toxicity Test Using the EpiAirwayIn VitroHuman Airway Model

“…In line with these goals, U.S. government regulatory agencies consider the development and validation of alternative in vitro methods for acute toxicity testing, including acute inhalation toxicity testing, to be a high priority. 13 The U.S. EPA has a stated goal of reducing in vivo testing for the acute toxicity “six-pack,” which includes acute inhalation testing of required tests for pesticides. 14 , 15…”