title: Adverse outcome pathway development II: best practices.
abstract: Organization of existing and emerging toxicological knowledge into adverse outcome pathway (AOP) descriptions can facilitate greater application of mechanistic data, including those derived through high-throughput in vitro, high content omics and imaging, and biomarker approaches, in risk-based decision making. The previously ad hoc process of AOP development is being formalized through development of internationally harmonized guidance and principles. The goal of this article was to outline the information content desired for formal AOP description and some rules of thumb and best practices intended to facilitate reuse and connectivity of elements of an AOP description in a knowledgebase and network context. For example, key events (KEs) are measurements of change in biological state that are indicative of progression of a perturbation toward a specified adverse outcome. Best practices for KE description suggest that each KE should be defined as an independent measurement made at a particular level of biological organization. The concept of "functional equivalence" can help guide both decisions about how many KEs to include in an AOP and the specificity with which they are defined. Likewise, in describing both KEs and evidence that supports a causal linkage or statistical association between them (ie, a key event relationship; KER), best practice is to build from and contribute to existing KE or KER descriptions in the AOP knowledgebase rather than creating redundant descriptions. The best practices proposed address many of the challenges and uncertainties related to AOP development and help promote a consistent and reliable, yet flexible approach.
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium villeneuve.dan@epa.gov.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Villeneuve
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Doug
authors.initials: D
authors.lastname: Crump
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Natàlia
authors.initials: N
authors.lastname: Garcia-Reyero
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Markus
authors.initials: M
authors.lastname: Hecker
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Hutchinson
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Carlie A
authors.initials: CA
authors.lastname: LaLone
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Brigitte
authors.initials: B
authors.lastname: Landesmann
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Teresa
authors.initials: T
authors.lastname: Lettieri
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Sharon
authors.initials: S
authors.lastname: Munn
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Nepelska
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Ottinger
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Lucia
authors.initials: L
authors.lastname: Vergauwen
authors.affiliation: *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville, MS 39762, School of the Environment and Sustainability and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada SK S7N 5B3, School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, UK, Water Resources Center, University of Minnesota, St. Paul, MN 55108, European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy, Department of Biology and Biochemistry, University of Houston, Houston, TX 77004, Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium *US EPA Mid-Continent Ecology Division, 6201 Congdon Blvd, Duluth, MN 55804, Environment Canada, Ecotoxicology and Wildlife Health Division, Ottawa, Ontario, Canada K1A 0H3, Institute for Genomics, Biocompu
authors.forename: Maurice
authors.initials: M
authors.lastname: Whelan
mesh_terms: D000818:Animals; D035843:Biomedical Research / Q000379:methods* / Q000706:statistics & numerical data; D016208:Databases, Factual; D006801:Humans; D008954:Models, Biological; D014116:Toxicology / Q000379:methods* / Q000706:statistics & numerical data
keywords: adverse outcome pathway; extrapolation; knowledgebase; predictive toxicology; regulatory toxicology