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Section E
In Vitro Toxicity Tests: Cellular Toxicity
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Examples of Cell-Based In Vitro Assays
! Hepatocyte/liver slice cultures
- Metabolism, genotoxicity, cytotoxicity
! Fibroblast/cell line cultures
- Cytotoxicity
! Three-dimensional cell cultures
- Skin, eye irritation tests
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Cellular Toxicity
Examples: In Vitro Methods which Replace Animal Use for Toxicity
Testing
In vitro assay
Whole animal
test replaced
Reduction in
animal use
EPIDERMTM skin corrosivity test—
Rabbits
reconstituted human skin
Total*
EPISKINTM corrosivity test
Rabbits
Total*
CorrositexR
Rabbits,
Rodents
Total*–in use by
DOT
Embryonic stem cell test
Rodents
Total*
In vitro 3T3 NRU phototoxicity
test
Rabbits,
Rodents
Total*
* Validated and recommended for regulatory use. See http://ecvam.jrc.it/index.htm, Web site for the European Center
for the Validation of Alternative Methods; See http://iccvam.niehs.nih.gov/, Web site for the U.S. Interagency
Coordinating Committee on the Validation of Alternative Methods.
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Episkin®
! Episkin® was developed by IMEDEX and L’OREAL
- In vitro reconstructed human epithelium
Source: http://www.imedex.fr/Episkin.htm
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Major Advantages of In Vitro Systems
! Reduced cost
! Reduction in animal use
! Greater experimental control over chemical
concentrations, environmental composition
! Uniform biological systems (cell lines)
! Ability to use human tissue/cells
! Potential for use in high-through-put screening assays
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Major Disadvantages of In Vitro Systems
! Loss of organ structure and cell-cell interaction
! Loss of differentiated tissue/cell-specific function
! Short term
! Static regarding nutrient influx, metabolite accumulation
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Toxicity Testing Challenges
! Universe of chemicals that require testing for potential
adverse health and environmental effects is enormous
- 87,000 chemicals candidates for screening for
endocrine disruption activity
- 30,000 chemicals in the REACH program
(Registration, Evaluation and Authorization of
Chemicals in the EU)
! Current assays take too long and are too costly in terms
of dollars and animals
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Future Directions in Toxicity Testing
! NRC/NAS report on “Toxicity Testing in the 21st Century:
A Vision and a Strategy,” 2007
- New in vitro cell systems
- New high-through-put systems
- Dose-response and extrapolation modeling
! PBPK models
- Population-based and human exposure data
! ! Application of “omics” (genomics, transcriptomics,
proteomics, metabolomics) to identify biomarkers
New animal models; humane end points
- Transgenic animals
- Use of less sentient species
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Future Directions in Toxicity Testing
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Additional Challenges: Development and Use of
New Tests
! Research to uncover mechanism-based pathways to
toxicity
! Development of mechanism-based assays
! Sorting out value of correlative vs. mechanism-based
tests
! Validation
! Regulatory acceptance
! Harmonization
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