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Report from working group on in vitro tests for chromosomal aberrations
S M Galloway1, M J Aardema, M Ishidate
1Merck Research Laboratories, West Point, PA 19486.
Mutation Research
|June 1, 1994
Summary
This working group provides consensus guidelines for chromosomal aberration testing, focusing on metabolic activation, exposure limits, and cytotoxicity assessment to ensure reliable genotoxicity data. Key recommendations include standardized S9 activation, defined concentration limits, and concurrent cytotoxicity measurements for accurate aberration scoring.
Area of Science:
- Genotoxicity testing
- In vitro toxicology
- Regulatory science
Background:
- The OECD guideline (473) for in vitro chromosomal aberration assays requires standardized protocols for reliable genotoxicity assessment.
- Working group consensus was sought on critical parameters to ensure reproducibility and accuracy in these assays.
Framework:
- Metabolic activation using S9 from induced animals (Aroclor 1254 or phenobarbital/beta-naphthoflavone) is acceptable; alternative systems require justification.
- Recommended upper testing limit is 10 mM or 5 mg/ml (lower of the two), with justification needed for deviations.
- Cytotoxicity must be assessed concurrently with aberration scoring using cell counts or confluence, not solely mitotic index.
Implementation:
- At least three concentrations should be scored for aberrations (with and without S9), spanning a toxicity range down to minimal cytotoxicity.
- Cytotoxicity at the top dose should ideally exceed 50% of controls, within the concentration limits.
- Consensus was not reached on whether solubility or cytotoxicity should be the primary limiting factor for top dose selection.
Implications:
- Standardized protocols enhance the reliability and comparability of genotoxicity data across laboratories.
- Clear guidelines for exposure concentrations and cytotoxicity assessment improve the accuracy of chromosomal aberration assays.
- Further discussion is needed regarding solubility limits to refine testing protocols.