Quantitative Adverse Outcome Pathway Assisted Risk Assessment of Mitochondrial Toxicants

Harmful chemicals released into the environment can have negative impacts on human and ecosystems. The current safety assessment of chemicals relies heavily on information obtained from standardized laboratory toxicity tests. However, due to the high number of chemicals (>147 million in the CAS registry), it is not feasible, cost-effective and ethical to perform tests for all chemicals. In addition, a transition towards reduced laboratory animal use with better animal welfare considerations is highly encouraged by both established chemical regulatory frameworks (e.g., REACH) and recent initiatives (e.g., the new Norwegian Animal Welfare Act). New Approach Methodologies (NAMs) with a cost-effective nature and full implementation of the 3R (Replacement, Reduction and Refinement) principles, such as high-throughput cell-based bioassays, high-content genomic tools and computational prediction/extrapolation models (e.g., quantitative Adverse Outcome Pathway/qAOP) are urgently needed to improve current chemical risk assessment and regulatory processes. RiskAOP is a proof-of-concept project aiming to demonstrate how NAMs can be used to refine conventional toxicity tests, and how novel computational/mathematical models such as qAOPs can be developed based on available experimental data and applied to predict the risks of chemicals. The project has a special focus on chemicals causing dysfunctions of the mitochondrion (a key cell organelle for energy production and cell survival) in key freshwater organisms (duckweed, water flea and zebrafish) representing different trophic levels. RiskAOP is hosted by Norwegian Institute for Water Research (NIVA). The project team consists of national and international experts in (eco)toxicology, physiology, chemistry and computational/mathematical modeling with a common goal to reduce laboratory animal tests, refine chemical risk assessment and improve environmental quality for both human and wildlife. RiskAOP has published a number of important articles in high-impact journals such as Environmental Science & Technology and Journal of Hazardous Materials. One of the AOPs has been endorsed by the OECD WPHA/WNT and published on the OECD website. The project participants have been actively involved in various types of workshops and seminars related to alternatives to animal testing and next generation risk assessment approaches. For more information, please visit the project website (https://www.niva.no/en/projectweb/riskaop).

Due to the high number of chemicals and species in the world, it is not possible to assess the risk of every chemical to human and ecosystems. Cost-effective ecotoxicity testing strategies with reduced laboratory animal use are highly demanded. New Approach Methodologies (NAMs), such as high-throughput screening and high-content toxicogenomics tools, in combination with quantitative Adverse Outcome Pathways (qAOPs), mathematical/computational prediction models that capture the complexity of toxicological responses across multiple levels of biological organization, are potential solutions to more cost-efficient ecological risk assessment (ERA) of chemicals and reducing laboratory animal tests. The RiskAOP project is therefore proposed as a proof-of-concept study to develop qAOPs and evaluate their applicability in ERA, using chemical-mediated mitochondrial dysfunction as a demonstrative case. The RiskAOP project has an overarching goal to demonstrate the usefulness of qAOPs and NAMs for ERA and regulatory decision-making. The objectives are: 1) Develop new AOP networks and associated NAMs for testing of mitochondrial toxicants; 2) Generate new experimental data for mechanistic and quantitative understanding of chemical-mediated mitochondrial dysfunction across different trophic levels; 3) Develop novel qAOP network models and evaluate their robustness and applicability for hazard assessment towards regulatory needs; 4) Propose new strategies for qAOP assisted risk assessment and regulatory decision-making. The RiskAOP project has a high ambition level due to its highly innovative nature. The proposed activities and anticipated outputs may potentially have great impact on both research and society, such as generation of new knowledge, tools and concepts, promotion of alternative approaches to animal testing and arousing public awareness on environmental contamination.