1 / 57

Reactive Toxicity : Progress Report on Filling the Gap G ilman Veith Logan UT March 23-24,2010

Reactive Toxicity : Progress Report on Filling the Gap G ilman Veith Logan UT March 23-24,2010. Facilitate promising QSAR technologies for setting priorities (TIMES-SS, Multipath, ASTER, OECD Toolbox)

bern
Download Presentation

Reactive Toxicity : Progress Report on Filling the Gap G ilman Veith Logan UT March 23-24,2010

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Reactive Toxicity: Progress Report on Filling the GapGilman VeithLogan UTMarch 23-24,2010

  2. Facilitate promising QSAR technologies for setting priorities (TIMES-SS, Multipath, ASTER, OECD Toolbox) Encourage the expansion of public domain databases and software for QSAR applications (ECOTOX, ER mediated toxicity) Develop high quality databases for QSAR modeling (inhalation for fish and rodents, nucleophile reactivity profiles) Provide QSAR training for regulators, business experts and students QSAR Foundation Goals

  3. Review progress on developing a systematic database for GSH reactivity Review progress on linking GSH reactivity to important hazard assessment endpoints Explore progress and options in selecting the next model nucleophile Explores possibilities for creating next systematic reactivity database. Logan Workshop Goals

  4. Review the context for using QSAR in regulatory safety assessments in relation to drug design Summarize hazard assessment endpoints which can be modeled by QSAR methods and those that cannot. Review our conceptual framework for modeling long-term adverse outcomes needed in risk assessment Summarize progress on integrating QSAR with toxicity pathways for predictive hazard identification. Purpose of this Overview

  5. -Screening Information Datasets – SIDS -Globally Harmonised System of C&L – GHS -Registration, Evaluation, Authorisation and Restriction of Chemicals – REACH -PMNs – OPPT (predictive hazard identification)Testing Requirements – OPP Initial Hazard Assessments

  6. QSAR Endpoints (SIDS) Physicochemical Properties and Fate • Melting Point • Boiling Point • Vapour Pressure • Log K o/w • Log K orgC/w • Water Solubility • Biodegradation Rates • Hydrolysis Rates • Atmospheric Oxidation Rates • Bioaccumulation

  7. QSAR Endpoints (~SIDS) Human Health Effects • Acute Oral Toxicity • Acute Inhalation Toxicity • Acute Dermal Toxicity • Skin/Eye Irritation • Skin Sensitisation • Repeated Dose Toxicity • Reproductive Toxicity • Developmental Toxicity • Genotoxicity (in vitro) • Genotoxicity (in vitro, non bacterial) • Genotoxicity (in vivo) • Carcinogenicity

  8. QSAR Endpoints (SIDS) Ecological Effects • Acute Lethality – Fish (many species) • Chronic Toxicity - Fish • Acute Lethality - Daphnid • Phytotoxicity, Growth Inhibition - Algae • Repeated Dose Effects - Mammals

  9. Gaps in QSAR Models • QSAR models have been developed for well-defined in vivo endpoints (steady-state exposures) • “Well-defined” excludes most long-term in vivo endpoints and most mammalian tests • >10,000 QSAR models for in vitro endpoints not yet reliably scaled to in vivo potency • QSAR-based Chemical Categories bridge some of these gaps while toxicity pathways are developed

  10. Estimating Aquatic Toxicity 2 LC50-96hr MATC-30 day Water Solubility 0 -2 Log Molar Concentration -4 -6 -8 -2 0 2 4 6 8 Log P

  11. Estimating Aquatic Toxicity 2 LC50-96hr Water Solubility 0 -2 Log Molar Concentration -4 -6 -8 -2 0 2 4 6 8 Log P

  12. LogLC50for fish or rat vs Solubility in water or air

  13. Framework for Estimating Toxicity 2 LC50-96hr Water Solubility 0 Baseline Toxicity -2 “Excess” Toxicity Log Molar Concentration -4 -6 -8 -2 0 2 4 6 8 Log P

  14. Which Conformation should we use to model interactions?

  15. Why “Reactive Toxicity”? • Nonspecific Narcosis QSAR in 1980 • Covers 60-70% of Industrial Chemicals • Hundreds of QSARs for Physical Toxicity • Largest Gap is Nonspecific Reactive Chemicals • Little Progress in Modeling Reactive Toxicity • Many Effects Endpoints for of Reactive Chemicals

  16. Our Conceptual Framework Chemical Speciation and Metabolism Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical

  17. Our Conceptual Framework Speciation and Metabolism Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical Response Pathways Chemistry/ Biochemistry QSAR 1. Identify Plausible Molecular Initiating Events 2. Design Database for Abiotic Binding Affinity/Rates 3. Develop QSARs to Predict Initiating Event from Structure 4. Quantify Response Pathways to Downstream Effects

  18. Conceptual Framework Chemical Speciation and Metabolism Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical Mortality -systemictoxicity -disease -cancer Impaired Development -terata -prenatal deficits Reproductive Fitness -fertility -viable offspring • Interaction • Mechanisms • -Nonspecific • Targets • Atom Centers • Targets • -Receptor • Targets Chemical Inventories and Categories (~200,000)

  19. At the Molecular Initiating Event Chemical Speciation and Metabolism Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical The QSAR Question is: “How many other chemicals can interact at this target?” While the Toxicology Question is: “What are the known biological effects from this altered target… cell type, organ, species ”

  20. From the Library of Initiating Events Chemical Speciation and Metabolism Library Of Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical OECD Toolbox Chemical Profiler Handles the Chemistry for QSAR Models Conformations Targets Interactions Metabolic Simulators Inventories Structural Requirements

  21. From the Library of Initiating Events Chemical Speciation and Metabolism Library Of Molecular Initiating Events Measurable Biological Effects Adverse Outcomes Parent Chemical Altered Gonad Development Gene Activation ER Binding Impaired Reproduction Protein Production

  22. Molecular Initiating Event Macro -Molecular Interactions Toxicant Chemical Reactivity Profiles Receptor, DNA, Protein Interactions Biological Responses Mechanistic Profiling The Adverse Outcome Pathway

  23. Molecular Initiating Event Biological Responses Macro -Molecular Interactions Toxicant Cellular Chemical Reactivity Profiles Receptor, DNA, Protein Interactions Gene Activation Protein Production Signal Alteration NRC Toxicological Pathway The Adverse Outcome Pathway

  24. Molecular Initiating Event Biological Responses Macro -Molecular Interactions Toxicant Cellular Organ Chemical Reactivity Profiles Receptor, DNA, Protein Interactions Gene Activation Protein Production Signal Alteration Altered Function Altered Development Mechanistic Profiling In Vitro & HTP Screening The Adverse Outcome Pathway

  25. Molecular Initiating Event Biological Responses Macro -Molecular Interactions Toxicant Cellular Organ Organism Population Chemical Reactivity Profiles Receptor, DNA, Protein Interactions Gene Activation Protein Production Signal Alteration Altered Function Altered Development Lethality Sensitization Birth Defect Reproductive Impairment Cancer Structure Extinction Mechanistic Profiling In Vitro & HTP Screening In Vivo Testing The Adverse Outcome Pathway

  26. Major Pathways for Reactive Toxicity from Moderate Electrophiles Interaction Mechanisms Molecular Initiating Events In vivo Endpoints Exposed Surface Irritation Michael Addition Schiff base Formation SN2 Acylation Atom Centered Irreversible (Covalent) Binding Necrosis: Which Tissues? Pr-S Adducts GSH Oxidation GSH Depletion NH2 Adducts RN Adducts DNA Adducts Oxidative Stress Systemic Responses Skin Liver Lung Systemic Immune Responses Dose-Dependent Effects

  27. Representation ofER binding pocket (LBD), with 3 sites of interaction shown (A, B, C), and recepter protein amino acids involved in interactions with chemical ligands. T 347 C C E 353 H 524 A B R 394 J. Katzenellenbogen

  28. A_B Interaction T 347 C E 353 H 524 H CH3 H A B HO OH R 394 H H Distance = 10.8 for 17-Estradiol J. Katzenellenbogen

  29. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements across levels of biological organization In vivo INDIVIDUAL Reproductive Impairment

  30. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements across levels of biological organization In vivo POPULATION INDIVIDUAL Skewed Sex Ratios; Yr Class Sex reversal; Altered behavior; Repro.

  31. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements across levels of biological organization In vivo POPULATION TISSUE/ORGAN INDIVIDUAL Skewed Sex Ratios; Yr Class Liver Altered gene products (timing, amt) Gonad Ova-testis; Sex-reversed; Fecundity Sex reversal; Altered behavior; Repro.

  32. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements across levels of biological organization In vivo POPULATION CELLULAR Response TISSUE/ORGAN INDIVIDUAL Skewed Sex Ratios; Yr Class Liver Altered gene products (timing, amt) Gonad Ova-testis; Sex-reversed; Fecundity Sex reversal; Altered behavior; Repro. Liver Cells Altered Protein Expression (marker) (effect) Vitellogenin

  33. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements across levels of biological organization In vivo POPULATION CELLULAR Response TISSUE/ORGAN MOLECULAR Target INDIVIDUAL Skewed Sex Ratios; Yr Class Liver Altered gene products (timing, amt) Gonad Ova-testis; Sex-reversed; Fecundity Sex reversal; Altered behavior; Repro. Liver Cells Altered Protein Expression (marker) (effect) Vitellogenin Receptor Binding ER-Chemical Binding

  34. Adverse Outcome Pathway ER-mediated Reproductive Impairment Measurements made across levels of biological organization QSAR focus area In vitroAssay focus area Risk Assessment Relevance Toxicological Understanding In vivo POPULATION CELLULAR Response TISSUE/ORGAN MOLECULAR Target INDIVIDUAL Skewed Sex Ratios; Yr Class Liver Altered proteins Gonad Ova-testis; Sex-reversed; Fecundity Sex reversal; Altered behavior; Repro. Liver Cells Altered Protein Expression Vitellogenin Receptor Binding ER Binding Chemicals

  35. In-vitro pathway Schmieder et.al. Cellular Organ Individual Population Molecular • AAN bindingto ER • Altered reproduction • Altered development • Liver sliceVtg (mRNA) • Liver slice toxicity • ER transcription factor Decreased numbers of animals ER-mediated Adverse-outcome Pathway Amylaniline (AAN) In-vivo pathway Multigen assay Individual Molecular Cellular Organ Population ♂ Liver Vtg (mRNA) dose: Sex reversal (altered gamete ratios) AAN bindingto ER ER transcriptionfactors Altered sex-ratios ? Anal fin papillae ? dose: Mixed-sex gonad ? Gonadal morphology Population reduction ? ? dose: Reduced fecundity AAN bindingto Hbg ? ? Splenic/head-kidney pathology ? dose: Reduced growth

  36. Thyroid MOAs

  37. Hearing Loss from Dioxins, Furans and PCBs (Planar Risk) Binding to PXR Hepatic Parent or Metabolite Exposure Hepatic Phase II Enzymes Binding to AhR Alter TR Mediated Proteins Loss of cochlear hair cells  Serum T4 & T3  Tissue T3 Hearing Loss

  38. “Narcosis”Pathways for Volatile Anesthetics Primary Brain Region Ion Channel Receptor Behavioral Effects Cellular Response Tissue Response GABAA Increased channel-open time Facilitated inhibitory transmission Cortex - Thalamus Light Sedation Amnesia Anxiolysis Heavy Sedation Slow responses nACh Reduced excitatory transmission Decreased channel-open time Hippocampus Agent Increasing Depth of Anesthesia Reduced membrane current Brain Stem Reduced excitatory transmission Unconsciousness Loss of perceptual awareness NMDA Glycine Increased duration of mIPSCs Facilitated inhibitory transmission Spinal Cord Immobility Loss of pain response Kinetics Dynamics

  39. ImmobilityPathway for Isoflurane Increasing Depth of Anesthesia Primary Brain Region Ion Channel Receptor Behavioral Effects Cellular Response Tissue Response GABAA Increased channel-open time Cortex - Thalamus Light Sedation Amnesia Anxiolysis Facilitated inhibitory transmission Heavy Sedation Slow responses nACh Reduced excitatory transmission Decreased channel-open time Hippocampus Agent Reduced membrane current Brain Stem Reduced excitatory transmission Unconsciousness Loss of perceptual awareness NMDA Glycine Increased duration of mIPSCs Facilitated inhibitory transmission Spinal Cord Immobility Loss of pain response Kinetics Dynamics

  40. Amnesia Pathway for Isoflurane Increasing Depth of Anesthesia NMDA Primary Brain Region Ion Channel Receptor Behavioral Effects Cellular Response Tissue Response GABAA Increased channel-open time Cortex - Thalamus Light Sedation Amnesia Anxiolysis Facilitated inhibitory transmission Heavy Sedation Slow responses nACh Reduced excitatory transmission Decreased channel-open time Hippocampus Agent Reduced membrane current Brain Stem Reduced excitatory transmission Unconsciousness Loss of perceptual awareness Glycine Increased duration of mIPSCs Facilitated inhibitory transmission Spinal Cord Immobility Loss of pain response Kinetics Dynamics

  41. Effectopedia Cause Link Effect

  42. Pathways for Reactive Toxicity Molecular Initiating Events In vitro Endpoints Interaction Mechanisms In vivo Endpoints Membrane Alteration _ _ _ Oxidative Stress _ _ _ Genotoxicity Death Impaired Growth Impaired Development Impaired Reproduction Michael Addition Schiff base Formation SN2 Acylation Atom Centered Irreversible (Covalent) Binding Pr-S Adducts GSH Oxidation GSH Depletion NH2 Adducts RN Adducts DNA Adducts Dose-Dependent Pathways Species/Sex/Life-Stage

  43. Two Questions for Building Pathways Direct Reaction Effect #1 Pr-S Adducts GSH Oxidation GSH Depletion NH2 Adducts RN Adducts DNA Adducts Altered Synthesis Effect #2 Oxidation Effect #3 How Many Ways to Deplete GSH? How Many Downstream Effects?

  44. Delineation of Toxicity Pathways Linkages Across Levels of Biological Organization In vivo Methods In vitro Methods In Silico Methods Molecular/ Subcellular Electronic Cell Tissue Organ Individual Exposure/ Metabolism Penetration Routes Detoxification Pathways Activation Pathways Chemical Reactivity Profiles Reversible Nonspecific Binding Reversible Specific Binding Covalent Binding Response Pathways Regulatory Endpoints Chemical Inventories Molecular Initiating Events Membranes Energy Charge Nuclear Receptors Protein Synthesis DNA Integrity Lethality Growth Development Reproduction More Relevant Endpoints Intrinsic Chemical Attributes Better Defined Endpoints

  45. Major Pathway for Reactive Toxicants To Fish Vulnerable Organ Pathology Molecular Initiating Events Interaction Mechanisms In vivo Endpoints Pathogenesis Michael Addition Schiff base Formation SN2 Acylation Atom Centered Irreversible (Covalent) Protein Binding Death from Suffocation “Any Exposed Surface” Changes Necrosis of the Gill Epithelium Complexes Membranes, etc

  46. Pathways for Reactive Toxicity from Soft Electrophiles Mechanisms Molecular Initiating Events In vivo Endpoints Michael Addition Schiff base Formation SN2 Acylation Atom Centered Irreversible (Covalent) Protein Binding Exposed Surface Irritation Necrosis Skin Lung/Gills GI Tract No Immunogenic Systemic Immune Responses Systemic Responses Skin Liver Lung Yes

More Related