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Historical vehicle and positive control micronucleus data in mice and rats
G Krishna1, G Urda, J Paulissen
1Department of Worldwide Preclinical Safety, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, 2800 Plymouth Road, Ann Arbor, MI 48105, USA. gopala.krishna@wl.com
Abstract:
The rodent bone marrow micronucleus (MN) assay has been widely used as part of an in vivo genotoxicity test battery in product safety evaluation. In this assay, the historical vehicle and positive control data form an important component in the assay performance and data interpretation. Also, in light of minimizing animal use in research and still obtain required data from a study, the routine use of positive control in every MN assay has been questioned by the scientific community, especially in laboratories which have demonstrated assay reproducibility and conduct studies under Good Laboratory Practice regulations. In this paper, mouse and rat vehicle and positive control MN data, collected manually, are described as a reference for a period of 12 years (1987-1998) in our laboratory. The vehicles generally included a variety of aqueous solutions and suspensions and cyclophosphamide dosed intraperitoneally at 20mg/kg (rats) or 40 mg/kg (mice) served as positive control, in all studies. Based on combined sex data (430 animals), for CD(1) mice, the vehicle control MN polychromatic erythrocyte (PCE) range was 0.9-3.1 with a mean of 1.75 per 1000 PCE and the positive control range (220 animals) was 8.8-42.1 with a mean of 23.1 MNPCE per 1000 PCE. Similarly, for Wistar rats, the vehicle control range (360 animals) was 1.3-5.3 with a mean of 2.6 MNPCE per 1000 PCE and the positive control range (240 animals) was 10.4-33.8 MNPCE per 1000 PCE. Vehicle control ranges reported here are comparable to the literature database and the positive control response was > or = 4-fold over vehicle control, in all studies. These data demonstrate the reproducibility of positive control response in MN assay in our laboratory and support the MN Assay Expert Panel's view that the use of positive control may not be necessary in every study.
Insights
The rodent bone marrow micronucleus (MN) assay is crucial for genotoxicity testing. Historical data show reproducible positive control responses, suggesting routine use may not be necessary, aligning with efforts to minimize animal use in research.
Area of Science:
- Toxicology
- Genetics
- In vivo assays
Background:
- The rodent bone marrow micronucleus (MN) assay is a standard in vivo genotoxicity test for product safety.
- Historical vehicle and positive control data are vital for assay performance and interpretation.
- Minimizing animal use in research has led to questioning the routine use of positive controls in MN assays, especially under Good Laboratory Practice (GLP) regulations.
Purpose of the Study:
- To describe 12 years of historical mouse and rat vehicle and positive control MN data as a reference.
- To evaluate the reproducibility of positive control responses in the MN assay.
- To support the view that positive controls may not be required in every MN assay study.
Main Methods:
- Manual collection of mouse and rat micronucleus (MN) data over 12 years (1987-1998).
- Vehicle controls included various aqueous solutions and suspensions.
- Positive control involved intraperitoneal administration of cyclophosphamide (20mg/kg in rats, 40mg/kg in mice).
Main Results:
- For CD(1) mice (n=430), vehicle control MN polychromatic erythrocyte (PCE) range was 0.9-3.1 (mean 1.75/1000 PCE); positive control (n=220) range was 8.8-42.1 (mean 23.1/1000 PCE).
- For Wistar rats (n=360), vehicle control range was 1.3-5.3 (mean 2.6/1000 PCE); positive control (n=240) range was 10.4-33.8/1000 PCE.
- Positive control responses were consistently ≥4-fold over vehicle controls, demonstrating assay reproducibility.
Conclusions:
- The historical data demonstrate reproducible positive control responses in the MN assay within the laboratory.
- Vehicle control ranges align with existing literature.
- These findings support the MN Assay Expert Panel's perspective that routine positive control use may be unnecessary in every study.