Transcript Animal Models for Predicting Sensitization Potential

Animal Models for
Predicting Sensitization
Potential
Judith C. Stadler
Haskell Laboratory, DuPont Company
Newark, DE
Dermal Sensitization
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Regulatory Acceptance
– Guinea Pig
• Buehler
• Maximization Test
– Mouse
• Local Lymph Node Assay
Dermal Sensitization (continued)
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Other Tests
– Guinea Pigs
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Open Epicutaneous
Mauer Optimization Test
Split Adjuvant Technique
Freund’s Complete Adjuvant Test
Draize Sensitization
– Mice
• Mouse Ear Swelling Test
Guinea Pig Tests
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Based on common principles
– Chemical induction
– Rest phase
– Dermal Challenge
– Skin Reaction Assessment
• Erythema, edema,
Guinea Pig Tests
Buehler
Maximization
Induction
Method:
Topical
Application
ID Freunds
Adj. +Topical
Induction
Days:
0, 6-8, 13-15
5-8
Challenge
Method:
Topical, 6 hrs
Topical
Challenge
Days:
27-28
20-22
Rechallenge:
If equivocal
Guinea Pig Tests
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Advantages
– Measures skin reactions similar to human
response
– Large data base for comparison of many
chemicals
– Correlates well to human response
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Disadvantages
– Requires large numbers of animals
– Subjective evaluation
– Assessment of colored materials difficult
Mouse
Local Lymph Node Assay
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Based on responses during
induction rather than elicitation
phase of sensitization
Measures induction of the Tlymphocyte proliferative response in
skin draining lymph nodes
Local Lymph Node Assay
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Sequence of Events
– Topical application, generally to the ear
– Epidermal cells release cytokines
– Mobilize Langerhans’ cells
– Antigen transported from skin to draining
lymph nodes
– Responsive T-cells activated and divide
– Radioactivity incorporated during clonal
expansion
Local Lymph Node Assay
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Advantages
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Smaller numbers of animals required
Quantitative assay
Several doses can be evaluated
Colored materials can be assayed
Disadvantages
– Insoluble or systemically toxic materials may not
test well
– Tests not predictive for metals
Local Lymph Node Assay
Regulatory Status
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U.S. EPA has approved its use as a
stand-alone assay
Europe has approved for registrations if
the assay is positive. If the assay is
negative, a follow-up guinea pig assay
is required
– This requirement expected to change by
the end of 2000
Respiratory Sensitization
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No tests have been validated for
regulatory testing
Use of animal models primarily for
research and mechanistic studies
Evaluation of models for predictive
assays continues
Animal Models of Respiratory
Sensitization
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Some use as
predictive assays
– Mouse
– Guinea pig
– Rat
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Primarily used in
asthma research
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rabbit
dog
sheep
primate
Occupational respiratory allergic
disorders
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Wide spectrum of disease
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asthma
hypersensitivity pneumonitis
Pulmonary infiltrates with eosinophilia
Pulmonary institial fibrosis
Mechanisms
– IgE, IgG4, cell-mediated immunity
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Extent and duration of exposure related to
likelihood of sensitization
Guinea pig
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Similar to humans
– Histaminic bronchoconstriction at antigen
challenge
– Exhibits airways hyperreactivity
– Late-phase responses can be elicited
– Lung eosinophilia
Guinea pig use with chemical and
protein workplace allergens
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Isocyanates
– Various methods of induction
– Inhalation challenge with chemical or the
protein conjugates
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Detergent enzymes
– Inhalation induction model
– Intratracheal test
Guinea pig
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Advantages
– Ease of sensitization
– Immunologically robust
– Multifactorial
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Disadvantages
– IgG-dependent mechanism
– Hyper eosinophilia
– Dissociation between airway hyperreactivity and
eosinophilia
– Biological variability (outbred strains)
– Cost prohibitive
Mouse
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Similarities of the model to human
– Influx of eosinophils and T-cells
– histological features following acute
exposures similar to human
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Epithelial denudation
Interstitial airway edema
Thick basement membrane
Goblet cell hyperplasia
– Mucus hypersecretions
– Repeated exposure results in histological
features of chronic asthma
Mouse
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Advantages
– Molecular and immunological assays available
– Acute bronchoconstriction and airway
hyperreactivity can be elicited from antigen
challenge
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Disadvantages
– Large doses required for antigen challenge
– Difficult to measure eosinophil degranulation,
rarely in airways
Brown Norway Rat
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Similarities to human sensitization
– Serotonergic bronchoconstriction
– IgE mediated
– Early and late phase reactions
– Airway hyperreactivity
– Tissue + BAL accumulation of neutrophils,
eosinophils, lymphocytes
Brown Norway Rat
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Advantages
– Good inflammatory responses
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Disadvantages
– Induction of airway hyperreactivity difficult
Regulatory Status
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No one model has been validated for
prediction of respiratory sensitization
New concerns may place higher priority
on this area and encourage methods
validation
– Children’s Health issues
– Food allergy
Future direction
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Emphasis on structure-activity
relationships
Assay development
– molecular biology
– other in vitro screening
References/Suggested Reading
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OECD Guidelines for the Testing of Chemicals 406 Skin Sensitisation (17-JUL92)
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OPPTS Health Effects Test Guidelines. OPPTS 870.2600 Skin Sensitization (5AUG-98)
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Dearman, R.J. D.A. Basketter, and I. Kimber (1999) Local lymph node assay:
use in hazard and risk assessment REVIEW. J. Appl Toxicol. 19, 299-306.
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Kimber, I, I.L. Bernstein, M.H. Karol, M.K. Robinson, K. Sarlo, and M.K.
Selgrade (1996) Identification of respiratory allergens. Fund. and Appl Tox 33,
1-10.
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Padrid, Philip. Animal models of asthma. in Lung Biol. Health Dis. (1996),
96(Genetics of Asthma), 211-233.
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Selig, William M.; Chapman, Richard W. Asthma. in In Vivo Models of
Inflammation (1999), 111-135.