Adverse Outcome Pathways: A Framework for Organizing Mechanistic Information to Improve Chemical Assessment

Transcription

1 Adverse Outcome Pathways: A Framework for Organizing Mechanistic Information to Improve Chemical Assessment Kristie Sullivan, MPH Director, Toxicology and Regulatory Testing Issues

2 OUTLINE About Physicians Committee Why AOPs? OECD AOP Programme Case Examples Application to Tobacco Chemicals How to Get Involved

3 Physician-founded in 1985 Aims to increase scientific and ethical standards for medical education and research, and improve the public health Toxicology: modernize and improve

4 TOXICITY TESTING REVOLUTION

5 Toxicity Testing Revolution 5

6 TOXICITY TESTING REVOLUTION

7 Evolution of the Revolution 7

8 AOP: Organizational Framework

9 How are AOPs Used? Organize available evidence into context Link mechanistic data to adverse outcomes Highlight research needs Mechanistic support for chemical grouping and readacross to fill data gaps Put in vitro assays into regulatory context Create testing strategies/frameworks (IATA) Identify assay gaps/needs 9

10 Harmonized test guidelines and docs by >30 member countries Foundation for chemical characterization & tool support QSARs Test Guidelines Integrated Approaches to Testing and Assessment Expert group to develop, guide, and promote: Extended Advisory Group for Molecular Screening and Toxicogenomics (EAGMST) 10

11 AOP Elements KEY EVENTS KEY EVENT RELATIONSHIPS ADVERSE OUTCOME 11

12 AOP-Knowledgebase to collect information and allow collaboration International platform for review and publication Guidance Document and User s Handbook 12

13 AOPKB.org AOPWIKI.org AOP Wiki Collaborative development of AOP descriptions & evidence Effectopedia Detailed development of structured & computational AOPs AOP-KB AOP Xplorer Visualize attribute networks to discover & explore AOPs in a broader context Intermediate Effects DB Put chemical-related AOP components in a regulatory context Slide: Clemens Whittwher, JRC AOP-KB Hub Shared chemical, biological and toxicological ontologies Third party Applications, plugins

14 Figure 2. Overview of the organization of content pages in the AOPwiki relative to sections of the AOP template. Sections 1, 4, 5a, and 7 are found on the main page for an individual AOP. Information related to sections 5b and section 6 are entered into separate content pages that can be linked to multiple individual AOP pages. Section 5b MIE, KE, and AO descriptions Section 1 - Title Section 4 Abstract AOP Page Section 5a Summary of the AOP MIE Linkage table KEs AO KE Pages Description Measurement/ detection Taxonomic applicability MIE Page Chemical initiator(s) Description Measurement/ detection Taxonomic applicability Evidence for chemical initiation Key Event Relationships Applicability domain(s) of the AOP Life-stage Taxonomic Sex Section 7 Overall Assessment of the AOP Modified Bradford Hill Considerations Section 6 Scientific evidence supporting the linkages in the AOP Slide courtesy of Steve Edwards, EPA KER Pages Title Description Biological plausibility Empirical support Inconsistencies and uncertainties Quantitative understanding AO Page Description Measurement/ detection Taxonomic applicability Regulatory relevance AOP Wiki 14

15 PROPOSA L CREATION STATIC VERSION REVIEW Slide: Anne Gourmelon, OECD 15

16 APPLICATION Slide: Anne Gourmelon, OECD ENDORSEMENT AND PUBLICATION 16

17 How Are AOPs Developed? Open, stakeholder-inclusive effort Expert workshop setting By leading experts over time* One main team or lab Crowd-sourced Computationally-predicted 17

18 How Are AOPs Developed? MIE Key Event Key Event Key Event Adverse Outcome MIE Adverse Outcome 18

19 How Are AOPs Developed? AOP elements are interoperable and form networks

20 Pathway networks Chemical 1 MIE1 KE KE KE AO1 Chemical 2 MIE2 KE AO2 KE Chemical 3 MIE3 KE X KE AO3 Chemical 4 MIE4 KE Y KE AO4 Chemical 5 MIE5 KE KE KE AO5 Vulnerability analysis Toxicity of mixtures Alternative test prioritisation Slide: Hristo Aladjov and Joop DeKnecht, OECD Chemical2 Chemical4 Chemical5 concentration

21 AOP Wiki Authors: Malgorzata Nepelska, Sharon Munn, Brigitte Landesmann; Systems Toxicology Unit, Joint Research Centre, European Commission

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23 AOP Wiki

24 AOP Wiki

25 AOP Wiki

26 How are AOPs Developed? Computationally-predicted Automated literature searches Data-base mining High-content or high-throughput data sets Project 1.29: A catalog of putative AOPs that will enhance the utility of US EPA Toxcast high throughput screening data for hazard identification

27 How Are AOPs Developed? OECD Guidance: Guidance document on developing and assessing adverse outcome pathways (#184) + Handbook Villeneuve et al, Adverse Outcome Pathway (AOP) Development I: Strategies and Principles, Tox Sci 142(2), 2014, Villeneuve et al, Adverse Outcome Pathway Development II: Best Practices, Tox Sci, 142(2), 2014,

28 Sensitization of the Respiratory Tract (Project 1.20) Occupational Asthma Acute and chronic symptoms of upper and lower airways Sensitization and elicitation phase Sensitization can occur via dermal exposure Focus: LMW organic compounds 28

29 Sensitization of the Respiratory Tract AOP Project Kent Carlson, CPSC Stella Cochrane, Unilever Katherina Sewald, Fraun. ITEM Kristie Sullivan, PCRM Steve Enoch, LJMU Janine Ezendam, RIVM Ian Kimber, U of Manchester Grace Patlewicz, EPA Erwin Roggen, Novozymes 29

30 Sensitization of the Respiratory Tract AOP Project Motivations Regulatory need for assays to detect and distinguish respiratory sensitizers Mechanisms not as well understood Support development of in silico and in vitro TM 30

31 Initial Issues Sparse literature for LMW RS-chemicals Literature available for related, but separate pathways Skin Sensitization Metal complexes (e.g., chloroplatinates) Proteins Defining the Adverse Outcome Defining elements cohesively with skin AOP 31

32 LMW Organic Chemical Exposure MIE: Covalent Binding to Lysine Residues on Proteins Cellular Danger Signals: Activation of Inflammatory Cytokines and Chemokines and Cytoprotective Gene Pathways (Th2) Dendritic Cell Activation (Th2 Skewed) and Migration T-cell Activation-Proliferation-Polarization (Th2) AO: Sensitisation of the Respiratory Tract and Allergic Asthma upon Challenge

33 Slide: Katherina Sewald and Janine Ezendam Protein LMW agent LAR Effector T-cells Hapten-carrier complex SIGNAL 1 Recognition Uptake Processing of Antigen MIE Eosinophils Local antigen presentation to effector cells Naive dendritic cell KE 3a KE 3b Naive T-cell Matured dendritic cell SIGNAL 2 DANGER SIGNAL KE 2 Protein LMW agent DC-Th2 cell interaction KE 4 T-cell proliferation SIGNAL 3 B-cell activation Adverse Outcome Matured Th cell IL-4, IL-5, IL-13 IgE Mast cells Histamine EAR 33

34 Evaluating the AOP Biological Plausibility of KERs: Moderate Essentiality of KEs: Moderate Some blocking experiments for KEs 2 and 3 Empirical Support for KERs: Moderate Preponderance of evidence supportive Mechanistic studies in the literature are confined to one or a few hallmark sensitizers Temporality and quantitative information has been pursued in only a few studies 34

35 Research Gaps Dendritic cell polarization and T-cell effector response differs from skin sensitization why? There is some indication that binding site and protein preference sets Th2 response into motion Quantitative/Potency considerations Individual variation in attainment of AO 35

36 Chemical Exposure Covalent Binding to Proteins QSAR & structural alerts Peptide Reactivity [Lys/Cys depletion ratio] Cellular Danger Signals Dendritic Cell Activation and Migration Dendritic cellbased assays [surface markers, cytokines, gene expression/pr ofiling] Epithelial cells, Tissues [cytokine release, gene expression, oxidative stress] T-cell Activation- Proliferation- Polarization AO: Sensitisation of the Respiratory Tract In vivo assays: T- cell proliferation, IgE, hypersensitivity response 36

37 Skin and Respiratory AOPs MIE KE 2 KE 3 KE 4 AO Covalent Binding to Cysteine residues Covalent Binding to Lysine residues Cellular Danger Signals: Nrf2-ARE pathway vs. Th2 correlation DC activation Th2- skewed DC activation DC Migration Th1 T- cell Activatio n Th2 T- cell Activatio n Skin sensitiz -ation Resp. sensitiz -ation

38 AOPs for Tobacco Assessment Project 1.25: The Adverse Outcome Pathway from Induction of Secretion of Inflammatory Cytokines Leading to Lung Emphysema Smoke / Ingredient exposure-outcome (KERs) information Complex adverse outcomes amenable to AOP networks w/shared key events Systems toxicology evidence and sbv process can strengthen existing AOPs and connections

39 AOPs for Tobacco Assessment Highlight research needs Illuminate species or genetic differences Identify potential susceptible populations Generate hypotheses Prioritize future research based on essential missing information 39

40 AOPs for Tobacco Assessment Mechanistic support for alternative approaches to assess products Read-across with data from structurally similar constituents Rank constituents based on weight of evidence Rank products to support modified risk Target constituents for replacement 40

41 AOPs for Tobacco Assessment Create testing strategies/frameworks Put in vitro assays into regulatory context Chemical Stressor(s) Inflammation & Oxidative stress Ciliary Dysfunction & Ion Transport Irregularity Goblet Cell Hyperplasi a & Mucus Production Tissue Destruction & Remodeling Adversity vis a vis COPD 41

42 Non-governmental roles Scientific AOP Development Tool development AOP KB Education, outreach, and training Prizes!

43 Kristie Sullivan, MPH YouTube: AOP Learning Channel Thank you for your attention!

44 Willett et al Pathway-based toxicity: history, current approaches and liver fibrosis and steatosis as prototypes. ALTEX. doi: /altex Villeneuve et al 2014a. Adverse Outcome Pathway Development I: Strategies and Principles. Tox Sci. doi: /toxsci/kfu199. Villeneuve et al 2014b. Adverse Outcome Pathway Development II: Best Practices. Tox Sci. doi: /toxsci/kfu200. Adeleye et al Implementing Toxicity Testing in the 21st Century (TT21C): Making safety decisions using toxicity pathways, and progress in a prototype risk assessment. Toxicology. doi: /j.tox Tollefsen et al Applying Adverse Outcome Pathways to support Integrated Approaches to Testing and Assessment. Reg Tox Pharm. doi: /j.yrtph Bal-Price et al International STakeholder NETwork (ISTNET): creating a developmental neurotoxicity (DNT) testing road map for regulatory purposes. Arch Toxicol. doi: /s Patlewicz et al Proposing a scientific confidence framework to help support the application of adverse outcome pathways for regulatory purposes. Reg Tox Pharm. doi: /j.yrtph