Editor’s Highlight: Mechanistic Toxicity Tests Based on an Adverse Outcome Pathway Network for Hepatic Steatosis

Abstract

Risk assessors use liver endpoints in rodent toxicology studies to assess the safety of chemical exposures. Yet, rodent endpoints may not accurately reflect human responses. For this reason and others, human-based invitro models are being developed and anchored to adverse outcome pathways to better predict adverse human health outcomes. Here, a networked adverse outcome pathway-guided selection of biology-based assays for lipid uptake, lipid efflux, fatty acid oxidation, and lipid accumulation were developed. These assays were evaluated in a metabolically competent human hepatocyte cell model (HepaRG) exposed to compounds known to cause steatosis (amiodarone, cyclosporine A, and T0901317) or activate lipid metabolism pathways (troglitazone, Wyeth-14,643, and 22(R)-hydroxycholesterol). All of the chemicals activated at least one assay, however, only T0901317 and cyclosporin A dose-dependently increased lipid accumulation. T0901317 and cyclosporin A increased fatty acid uptake, decreased lipid efflux (inferred from apolipoprotein B100 levels), and increased fatty acid synthase protein levels. Using this biologically-based evaluation of key events regulating hepatic lipid levels, we demonstrated dysregulation of compensatory pathways that normally balance hepatic lipid levels. This approach may provide biological plausibility and data needed to increase confidence in linking invitro-based measurements to chemical effects on adverse human health outcomes.

Predicting the Probability that a Chemical Causes Steatosis Using Adverse Outcome Pathway Bayesian Networks (AOPBNs)

“…Predictions from the AOPBN for steatosis agreed with the results published in Angrish et al. () (Table ). It is important to recall that the AOPBN is completely independent of the data from Angrish et al.…”

“…Angrish et al. () confirmed that T0901317 and cyclosporin A both caused steatosis; the rest of the chemicals did not.…”

“…In this case, we are using data from Angrish et al. (). Note that the data used for validation were not used in model development.…”

“…Cytosolic fatty acids (measured using fluorescence intensities and the dyes Nile Red and Hoechst 33342, see Angrish et al. () for details) were decreased for only certain chemicals, therefore, those were scored as FALSE. We also used only the results for the highest concentrations as this is a hazard identification case study where we desired to detect any potential ability to cause steatosis.…”

“…Note that the efforts described here and those in Angrish et al. () were completely separate; none of the information from the Angrish et al. () study was used to develop the AOPBN presented here, making that data external to this validation study.…”