the role of genomics in mode-of-action based risk assessment · (2007) rat (wistar) 500 mg/kg/day...
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The Role of Genomics in Mode‐of‐Action Based Risk
Assessment
Ivan Rusyn, M.D., Ph.D.Associate Professor
Department of Environmental Sciences & Engineering
University of North Carolina
Chapel Hill, NC, USA
The genomes of more than 180 organisms have been sequenced since 1995. The Quick Guide includes descriptions of these organisms and has links to sequencing centers and scientific abstracts.
Genomenewsnetworks.org
Toxicogenomics: A routine component of the toxicology investigation
DATA
“Traditional”toxicological evaluation
Modified from Agilent Technologies® and other sources
Submitted by: Jack Vanden Heuvel, PhD
BIOCARTA PATWAY: Basic mechanism of action of PPARα, PPARβ(δ) and PPARγ and effects on gene expression
Cytoscape‐generated NETWORK(also referred to as INTERACTOME)
KEGG PATWAY: PPAR signaling
Ligand Transcription TargetFactor Gene
High‐Dimension Low Sample Size Data
SmartMoney.com
1983 1996 2007 2009
Risk Assessment: The evaluation of scientific information on:•the hazardous properties of environmental agents,•the dose‐response relationship, and •the extent of human exposure to those agents
The product of the risk assessment is a statement regarding the probability that populations or individuals so exposed will be harmed and to what degree
Hazard assessmentDose‐response assessmentExposure assessment
Risk characterization
Laboratory and field observations of
adverse health effects and exposures to particular agents
Information on extrapolation methods for high to low dose, and animal to human
Field measurements, estimated exposures, characterization of
populations
Hazard Assessment(Does the agent cause the
adverse effect?)
Dose‐Response Assessment(What is the relationship
between dose and incidence in humans?)
Exposure Assessment(What exposures are currently experienced or anticipated under different conditions?)
Risk Characterization(What is the estimated incidence of the adverse
effect in a given population?)
Development of regulatory optionsDevelopment of regulatory options
Considerations:•Public health•Statutory/Legal•Political•Economic•Social factors
Considerations:•Public health•Statutory/Legal•Political•Economic•Social factors
AGENCY DECISIONS AND ACTIONSAGENCY DECISIONS AND ACTIONS
RESEARCH RISK ASSESSMENT RISK MANAGEMENT
Modified from National Research Council, 1983
Hazard Assessment: The process of determining whether exposure to a stressor can cause an increase in the incidence of specific adverse health effects (e.g., diseases, cancer, birth defects) and whether the adverse health effect is likely to occur in humans
Sources of DataoStudies in humans:
• controlled exposures in volunteers• epidemiological data
oStudies in animals:• sub‐chronic, chronic and cancer bioassay studies• reproductive and developmental studies• other endpoint‐specific studies
oStudies in model organisms and cell‐based systems:• genotoxicity evaluation• studies of the toxicity pathways
Toxicokinetics Toxicodynamics
MODE OF ACTION:a sequence of key events
and processes, starting with interaction of an agent and a cell, proceeding through operational and anatomical changes, and resulting in a
pathological change
Modified from www.epa.gov
Dose‐Response Assessment:A determination of the relationship between the magnitude of an administered, applied, or internal dose and a specific biological response (measured or observed incidence or change, or the probability of occurrence or change)
Identify one or more principal studies and critical effects
Derive Reference Dose/Concentration:RfD (RfC) = POD / (U1 x U2 x U3)
Evaluate Mode of Action (MOA)
Animal to human dose conversion:scaling or pharmacokinetic modeling with pharmacodynamic adjustment
Derive POD (LED01, BMDL10, etc.) and Slope Factor (e.g., 0.01/POD)
Select Uncertainty/Adjustment Factors:•Intraspecies•Interspecies •Subchronic‐to‐Chronic Duration •Database•LOAEL‐to‐NOAEL
Identify NOAEL or LOAEL, or “Point of Departure (POD)”
MOA unknown Low Dose Linear
Low DoseNon‐linear
NON‐CANCERRisk Assessment
CANCERRisk Assessment
Modified from National Research Council, 2009
Exposure Assessment:• The process of measuring or estimating the magnitude, frequency, and duration of human exposure to an agent in the environment, or estimating future exposures for an agent that has not yet been released
• An exposure assessment includes some discussion of the size, nature, and types of human populations exposed to the agent, as well as discussion of the uncertainties in the above information
MODE OF ACTION:a sequence of key events
and processes, starting with interaction of an agent and a cell, proceeding through operational and anatomical changes, and resulting in a
pathological change
Modified from www.epa.gov
Current Efforts to Utilize Toxicogenomic Data in Risk
Assessment:
• Toxicogenomics informs Mode of Action analysis
• Toxicogenomics informs Dose‐Response
• Toxicogenomics informs interspecies extrapolations
• Toxicogenomics informs intraspecies variability
• TK/TD linkages informed by Toxicogenomic data
Potential uses of toxicogenomics data in chemical screening and risk assessment
EPA/600/R‐09/028F September 2009
From: Natsoulis et al. Molecular Systems Biology 4:175 (2008)
Toxicogenomics data informs chemical prioritization
Compile a large database of data on “known” toxicants profile an “unknown” agent
Toxicogenomics data informs Mode of Action analysis
EPA/600/R‐09/028F September 2009
Toxicogenomics data informs Mode of Action analysis
businessradar.it
Dibutyl Phthalate:Male Reproductive Developmental Toxicant
Known Modes of Action:odecrease in fetal testicular testosterone (T)odecrease in Insulin‐like 3 (Insl3) expression
EPA/600/R‐09/028F September 2009
Toxicogenomics data informs Mode of Action analysis
Case study of Dibutyl Phthalate Risk Assessment research questions:oDo the toxicogenomic data inform the mechanisms and/or modes of action? oDo the toxicogenomic data inform interspecies toxicodynamic differences? oDo the toxicogenomic data inform dose‐response?
Study Strain/species Dibutyl Phthalate dose Treatment interval Microarray RT‐PCR Tissues studied
Liu et al. (2005) Rat (SD) 500 mg/kg/day Gestation Days 12‐19 Affymetrix® Yes Testis
Thompson et al.(2005)
Rat (SD) 500 mg/kg/day(½ ‐24 hrs) on GD 18‐19; or
GD 19Affymetrix® Yes Testis
Plummer et al. (2007)
Rat (Wistar) 500 mg/kg/dayGDs 12.5‐15.5;
12.5‐17.5; or 12.5‐19.5Agilent® Yes
Testis (whole and anatomical regions)
Idh1LhgcrNr4a1SqleStc1Tpm1
Cdkn1cCrabp2Ddit4Dhcr7Dusp6Fabp3Frag1FthfdGrb14Gstm2Hsd3b1
Cyp11a1Cyp17a1Scarb1DdcFdx1Myh6Prdx3StarSvc5
Cyp51
Alas1Aldh2DbiFads1Fdft1FdpsFdxrGsta3HMGcrHmgsc1Idi1Stc2
InhaMe1Nr0b1Pebp1Por
Sc4molScp2
36 65
93Liu et al. (2005)
Thompson et al. (2005) Plummer et al. (2005) Dibutyl Phthalate:Male Reproductive System Toxicity (in the Rat)
Modes of Action:odecrease in fetal testicular testosterone (T)odecrease in Insulin‐like 3 (Insl3) expressionogrowth and differentiationotranscriptionocell adhesionoWnt signalingocytoskeleton remodeling
Newly identified putative pathways
Toxicogenomics data informs INTERspecies differences(Mode of Action considerations)
Heat map of the expression profile of probe sets in rat and human hepatocytes treated with coumarin
Limited overlap in response to Wy‐14,643 at individual gene level but major overlap at pathway level
Gene‐by‐gene comparisons Gene‐by‐gene vs. pathway comparisons
Upregulated genes Downregulated genes
Gene Ontology Gene Set Analysis
Rakhshandehroo et al., PLoS One. 2009 Aug 27;4(8):e6796Uehara et al., Mol Nutr Food Res. 2009 Dec 29;54(2):218‐227
Toxicogenomics data informs INTRAspecies differences(Mode of Action considerations)
~6,500
gene
sAcute treatment induced/All StrainsApoptosisActivation of MAPK signalingProtein phosphorylationIncrease enzyme catalytic activitySub‐chronic repressed/All StrainsTCA cycleAcyl‐CoA metabolismCytoskeleton biogenesis
Treatment‐independent/Strain‐specG protein‐coupled signalingTGFb3 receptor signalingIon channel activityCalmodulin bindingRNA polymerase transcriptionCell migration
Sub‐chronic induced/All StrainsActivation of metabolism (aldehyde dehydrogenase activ.)Innate immune responseG protein‐coupled signalingCytokine productionCell growth
Toxicogenomics data informs Dose‐Response(Mode of Action considerations)
Rouquie et al. Toxicol Sci. 2009 May;109(1):59‐65NOAEL
LOAEL
LOAEL
NOAEL
Standard and Toxicogenomic NOAELs for Rat Testicular Toxicity Induced by Flutamide
No Observed Transcriptional Effect Level
Establishing NOTEL:Human BEAS‐2B bronchial
epithelial cells were exposed to the genotoxic carcinogen N‐hydroxy‐PhIP (N‐hydroxy‐2‐
amino‐1‐methyl‐6‐phenylimidazo[4’5‐b] pyridine at doses spanning 6 orders of
magnitude
Zarbl et al., Chem Biol Interact. 2010 (In press)
dose
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gene B
gene C
pathway
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KEGG00100biosynthesis of steroids
Pathway Dose Response ProfilesBisphenol A exposure (male rat testis gene expression)
µg/kg/day
µg/kg/dayData from Naciff et al., Tox Sciences (2005)
Toxicogenomics data informs Dose‐Response(Mode of Action considerations)
Normal and Patho-biology
-omics
Genetics
Data Analysis Knowledge
Toxicogenomics data is an integral part of Mode of Action evaluation
1983 1996 2007 2009
EPA’s NextGen Risk Assessment:oWhat currently available new data and knowledge are not now used in risk assessment but potentially should be? oHow can this new type of information best be incorporated into risk assessments and utilized to inform risk managers? oWhat new policies and procedures are needed? oHow can we ensure the redesigned process is scientifically robust, consistent across assessments and matched to the risk context?
oWhat is adverse or with what confidence can we predict disease or increased susceptibility based on molecular events?oHow will exposure response be characterized?oHow will variability and uncertainty be evaluated?
ACToRToxCast
NTP Study Reports
ToxRefDB
Sending The Data To The Cyberspace: Who Will Find It?
Chemistry Space ‐Omics Data Space
HTS Data Space
In Vivo Toxicity Data Space