A Case Study on Integrating a New Key Event Into an Existing Adverse Outcome Pathway on Oxidative DNA Damage: Challenges and Approaches in a Data-Rich Area

Abstract

Adverse outcome pathways (AOPs) synthesize toxicological information to convey and weigh evidence in an accessible format. AOPs are constructed in modules that include key events (KEs) and key event relationships (KERs). This modular structure facilitates AOP expansion and network development. AOP development requires finding relevant information to evaluate the weight of evidence supporting each KER. To do this, the use of transparent/reproducible search methods, such as systematic review (SR), have been proposed. Applying SR to AOP development in a data-rich area is difficult as SR requires screening each article returned from a search. Here we describe a case study to integrate a single new KE into an existing AOP. We explored the use of SR concepts and software to conduct a transparent and documented literature search to identify empirical data supporting the incorporation of a new KE, increase in cellular reactive oxygen species (ROS), upstream of an existing AOP: "Oxidative DNA Damage Leading to Chromosomal Aberrations and Mutations". Connecting this KE to the AOP is supported by the development of five new KERs, the most important being the first adjacent KER (increase in ROS leading to oxidative DNA damage). We initially searched for evidence of all five KERs and screened 100 papers to develop a preliminary evidence map. After removing papers not containing relevant data based on our Population, Exposure, Comparator and Outcome statement, 39 articles supported one or more KERs; these primarily addressed temporal or dose concordance of the non-adjacent KERs with limited evidence supporting the first adjacent KER. We thus conducted a second focused set of searches using search terms for specific methodologies to measure these first two KEs. After screening, 12 articles were identified that contained quantitative evidence supporting the first adjacent KER. Given that integrating a new KE into an existing AOP requires the development of multiple KERs, this approach of building a preliminary evidence map, focusing evidence gathering on the first adjacent KER, and applying reproducible search strategies using specific methodologies for the first adjacent KER, enabled us to prioritize studies to support expansion of this data-rich AOP.

Keywords: DNA damage; adverse outcome pathways; genotoxicity; reactive oxygen species; toxicology.

FIGURE 1

AOPs that converge on KEs associated with genotoxicity were extracted from the AOP-wiki and adapted from those proposed by Sasaki et al. (2020). These AOPs were chosen to demonstrate the growing network of shared KEs and KERs that form a network leading to chromosome damage and mutations. A network of KEs leading to aneuploidy is being developed separately. MIEs: molecular initiating events.

FIGURE 2

Flow diagram of the adverse outcome pathway ‘Oxidative damage leading to mutations and chromosomal aberrations’ (Cho et al., 2022).

FIGURE 3

Flow diagram of the adverse outcome pathway “Oxidative damage leading to mutations and chromosomal aberrations” (Cho et al., 2022) with the inclusion of an upstream KE “increase in cellular ROS”, which represents the eventual consensus ROS KE, occurring after the multiple MIEs by which ROS are produced after toxicant exposure, and the resulting new KERs.

FIGURE 4

Flow chart showing the number of articles included and excluded at each step of the broad literature review.

FIGURE 5

Flow chart showing the number of articles included and excluded at each step of the specific literature search.