U'S' Department of Energy Low Dose Radiation Research Program Developing a Scientific Basis for Radi

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U.S. Department of Energy Low Dose Radiation
Research ProgramDeveloping a Scientific Basis
for Radiation Risk Estimates The Goal of the
DOE Low Dose Research Program
Antone L. Brooks Washington State University-
Tri Cities Richland, Washington 99352
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Presentation Goals

• Outline the Low Dose Program.
• Review Program research progress.
• Discuss paradigm shifts and their potential
  impact on standards.

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Why now?

• Standards have been set from high dose effects,
  but low dose effects have not been measurable
  until now
• New technological developments and biological
  discoveries have made it possible to study low
  dose effects

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Needed Shift in Research Emphasis
Low Dose Alteration of Homeostasis
High Dose Damage and Health Effects
Mechanisms of Action Science-based Standards

Common Pathways for Environmental Interaction
Repair and Protective Mechanisms
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DOE Low-Dose Radiation Research Program

• A 10 year program
• Focused on biological mechanisms of low-dose (lt
  0.1 Gy) and low dose-rate (lt 0.1 Gy / Yr)
  radiation
• International in scope (currently 54 projects)
• To develop a scientific basis for radiation
  standards
• http//lowdose.tricity.wsu.edu

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Key Research Areas

• Technological Advances
• Biological Advances

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Focus Areas of Research for the Program

• Radiation vs Endogeneous Damage
• Bystander Effects
• Radio-adaptive Responses
• Genomic Instability
• Genetic Susceptibility

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Clustered DNA DamagesQuantitative Gel Analysis
Radiation
A
B
Enzyme
Enzyme
C
D
Neutral Agarose Gel Electrophoresis
Sutherland
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Advances in Molecular Cytogenetics
Dose Response
Chromosome Paint
High dose rate
True single exchanges /cell
Low dose rate
3
1
2
Dose (Gy)
Lucas Cornforth
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Bystander Effects
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Cell Transformation
Sawant et al.2000
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Impact of Bystander Effects on Dose and Risk

• Risk of transformation in vitro
• Reponse is independent of the number of hit
  sites in vitro
• Non-uniform distribution of dose in vivo

Sawant et al 2001
Prise et al. 2002
Brooks et al. 1978
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The Influence of 239PuO2 Particle Size on the
Dose-Distribution in the Liver of Chinese
Hamsters
Citrate
0.44µm
0.84µm
0.17µm
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The Influence of Dose-Distribution from 239Pu on
the Induction of Chromosome Aberrations
Brooks et al
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Cumulative Liver Tumor Incidence After 239PuO2 or
239Pu Citrate Exposure
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Radiation-induced Changes in Gene Expression
Low Dose Rate
High Dose
Low Dose
In Vitro
Single dose
Time after exposure
Tissue type
In Vivo
Amundson
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DIFFERENCES IN TRANSCRIPTION PROFILES
BETWEEN LOW AND HIGH DOSE IRRADIATION IN
HUMAN LYMPHOBLASTOID CELLS
HLB Cell Line


1038





0.1 Gy
2Gy



274
68
160







Total gene set contains over 12,000 genes
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What Genes are Responsible for the Adaptive
Response ?
90
80
70
60
Aberrations
50
Observed
40
Expected
30
20
10
0
0
0.5
150
0.5 150
Dose cGy
Shadley and Wolff 1987
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What Genes are Activated at Low Dose to Reduce
Cell Transformation?
Transformation Frequency
0
10
20
30
40
50
60
70
80
90
100
Dose (cGy)
Redpath et al. 2001
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Genomic Instability

• Observed both in vivo and in vitro
• Evidence for thresholds
• Common trait in cancer progression

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Genomic Instability in vitro and in vivo

• Morgan- in vitro
• Cellular and cytogenetic instability induced at
  high and low dose rates
• Ullrich- in vivoLinking cellular and molecular
  instability to whole animals and populations

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Cytogenetic aberrations in colonies derived from
stem cells in marrow suspensions exposed to
?-particles or x-rays
Kadhim et al., 1992
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Genomic Instability Induced by Gamma Rays in
Mouse Mammary Epithelial Cells
R.L. Ullrich B. Ponnaiya, 1998
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Genomic Instability as a Function of Mouse
Strain (Black or White)
R.L. Ullrich B. Ponnaiya, 1998
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Genetic Susceptibility
Who is susceptible to radiation?
Rapid gene sequencing makes identification
possible.
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Genes involved in Radiation Sensitivity and
Cancer Susceptibility

• Can we identify them?
• How many genes are there?
• How prevalent are they in the population?
• How sensitive do they make the people?

Schwartz 2002
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Products of the Program

• Low dose data
• Awareness of unique low dose responses
• Scientific
• Regulatory
• Public
• Major paradigm shifts

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Observations Suggesting Major Paradigm Shifts

• Adaptive response vs additive or synergistic
  effects
• Hit theory vs. bystander effects
• Mutation vs. gene induction
• Single cell vs tissue responses

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How Does Radiation Interact with Cells?

• Past
• Hit theory
• Direct ionization
• Free radical formation

• Present
• Bystander effects
• Cell-cell communication
• Cell-matrix communication

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Mutation vs. Gene Induction
Gene Induction
Gene Mutation
Transient Change
Permanent Change
Gene Expression
Protein Production
Change in Phenotype Apoptosis Cell
Proliferation Cancer
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The Reductionist View
A Heterotypic Cell Biology
Hanahan and Weinberg 2000
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Gene Mutation and Expression in Cancer
Tissue Theory
Mutation Theory
Tissues suppress cancer.
Single cell origin of cancer
Normal
Normal
Gene Activation
Initiation
Down Regulation
Promotion
Progression
Progression
Gene Expression- a common event
Gene Mutation- a rare event
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Potential Impact of Research on Public Perception

• Provide scientific outreach
• Level of understanding increased
• Risk and fear put into perspective
• Scientific basis for standards

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How will this Research Impact Standards?
Genetic Susceptibility
Adaptive Response
Genomic Instability
Bystander Effects
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Summary

• Radiation risks from low levels of radiation
  exposure cannot be predicted with epidemiological
  studies alone.
• Combining advances in technology with those in
  cell and molecular biology make it possible to
  detect biological changes after low doses and
  dose-rates of radiation exposure.
• Understanding the role of these biological
  changes in cancer risk may or may not impact
  radiation protection standards, but will help
  ensure that the standards are based on scientific
  data and are both adequate and appropriate.