Adverse Outcome Pathways for Regulatory Applications: Examination of Four Case Studies With Different Degrees of Completeness and Scientific Confidence.
Adverse outcome pathways (AOPs) offer a pathway-based toxicological framework to support hazard assessment and regulatory decision-making. However, little has been discussed about the scientific confidence needed, or how complete a pathway should be, before use in a specific regulatory application. Here we review four case studies to explore the degree of scientific confidence and extent of completeness (in terms of causal events) that is required for an AOP to be useful for a specific purpose in a regulatory application: (i) Membrane disruption (Narcosis) leading to respiratory failure (low confidence), (ii) Hepatocellular proliferation leading to cancer (partial pathway, moderate confidence), (iii) Covalent binding to proteins leading to skin sensitization (high confidence), and (iv) Aromatase inhibition leading to reproductive dysfunction in fish (high confidence). Partially complete AOPs with unknown molecular initiating events, such as 'Hepatocellular proliferation leading to cancer', were found to be valuable. We demonstrate that scientific confidence in these pathways can be increased though the use of unconventional information (eg, computational identification of potential initiators). AOPs at all levels of confidence can contribute to specific uses. A significant statistical or quantitative relationship between events and/or the adverse outcome relationships is a common characteristic of AOPs, both incomplete and complete, that have specific regulatory uses. For AOPs to be useful in a regulatory context they must be at least as useful as the tools that regulators currently possess, or the techniques currently employed by regulators.
*Environmental Laboratory, US Army Engineer Research and Development Center, Vicksburg Mississippi; edward.j.perkins@usace.army.mil.
Edward J
EJ
Perkins
Institute of Integrative Biology, University of Liverpool, Liverpool, Merseyside L69 3BX, UK;
Philipp
P
Antczak
*Environmental Laboratory, US Army Engineer Research and Development Center, Vicksburg Mississippi;
Lyle
L
Burgoon
Institute of Integrative Biology, University of Liverpool, Liverpool, Merseyside L69 3BX, UK;
Francesco
F
Falciani
Mississippi State University, Institute for Genomics, Biocomputing and Biotechnology, Starkville, Mississippi;
Natàlia
N
Garcia-Reyero
Unilever, Colworth Science Park, Sharnbrook MK44 1LQ, UK;
Steve
S
Gutsell
Unilever, Colworth Science Park, Sharnbrook MK44 1LQ, UK;
Geoff
G
Hodges
JRC Institute for Health and Consumer Protection, Ispra, Italy.
Aude
A
Kienzler
University of Antwerp, Zebrafishlab, Universiteitsplein 1, 2610 Wilrijk, Belgium;
Dries
D
Knapen
Agilent Technologies, Washington, District of Columbia; and.
Mary
M
McBride
The Humane Society of the United States, Washington, District of Columbia, USA.
Catherine
C
Willett
D000818:Animals; D047072:Aromatase Inhibitors / Q000633:toxicity; D002274:Carcinogens, Environmental / Q000633:toxicity; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D019295:Computational Biology; D003226:Congresses as Topic; D003659:Decision Making, Organizational; D017449:Dermatitis, Allergic Contact / Q000209:etiology / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D054750:Ecotoxicology / Q000331:legislation & jurisprudence / Q000379:methods*; D004785:Environmental Pollutants / Q000633:toxicity*; D055317:Evidence-Based Practice; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000473:pathology; D006801:Humans; D008954:Models, Biological; D066150:Organisation for Economic Co-Operation and Development; D018570:Risk Assessment / Q000379:methods / Q000592:standards; D012867:Skin / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D023382:Toxicity Tests, Acute / Q000592:standards; D036401:Toxicity Tests, Chronic / Q000592:standards
D047072:Aromatase Inhibitors; D002274:Carcinogens, Environmental; D004785:Environmental Pollutants
hazard assessment; mode of action; regulatory toxicology; risk assessment; tox21