OECD TG 475 is the “Mammalian Bone Marrow Chromosomal Aberration Test” standard, i.e., the chromosomal aberration test on mammalian bone marrow, which is included in Section 4 (Health Effects) of the OECD Test Guidelines for the Testing of Chemicals. The test is used to evaluate the potential of a test substance to cause structural chromosomal aberrations in bone marrow cells under in vivo conditions.
The basic principle of the test involves the microscopic examination of changes in chromosome structure in metaphase cells obtained from the bone marrow following administration. The evaluation is typically performed on bone marrow from mice or rats. The test substance is administered via a suitable route; to induce metaphase arrest, colcemid or a similar agent is administered within an appropriate time frame. The bone marrow cells are harvested, and after hypotonic treatment, fixation, smear preparation, and staining, metaphase preparations are made.
The most important structural aberrations examined are:
Chromatid aberrations: chromatid breaks, chromatid exchange
Chromosomal aberrations: chromosomal breaks, fragments, ring chromosomes, discentric chromosomes, exchanges
- If necessary, numerical changes such as polypoidy can also be detected; however, the primary purpose of the test is to detect structural chromosome aberrations.
During data analysis, at least 100 well-spread metaphases per animal are typically examined. In addition, indicators such as the mitotic index may be used to assess the cytotoxic effect on the bone marrow. The experimental design includes a negative control, a solvent control, and appropriate positive control groups; the group size and dose determination are justified in accordance with OECD TG 475 and the relevant regulatory requirements.
Why is the test performed?
OECD TG 475 is conducted for the following scientific and regulatory purposes:
Identification of a genotoxic risk: Assessment of the test substance's potential to cause structural chromosomal aberrations in bone marrow
Evidence of a clastogenic effect: Assessment of clastogenic potential based on chromosome breaks and structural changes
Validation of In Vitro Results: In Vivo Follow-Up of Substances Found to Be Positive or Suspect in In Vitro Genotoxicity Tests
Support for Regulatory Documentation: Use in the Safety Assessment of Chemicals, Drugs, Pesticides, Biocidal Products, Medical Devices, and Biotechnology Products
Approach to Evidential Weight: Contribution to Risk Assessment in Conjunction with Other Genotoxicity Tests, Physicochemical Data, and Exposure Assessment
- Product Safety and Quality Assurance: Documentation of the biosafety profile of raw materials, intermediates, or finished products
OECD TG 475 is not a standalone carcinogenicity test. It is intended to identify a genotoxic risk; the results should be interpreted in conjunction with other in vivo and in vitro genotoxicity data.
As part of our nano-testing services, we conduct tests in accordance with OECD TG 475 with scientific rigor, leveraging our accredited laboratory infrastructure and quality management system. Our scope of services includes the following:
Study Design and Protocol Development
- Preparation of a study protocol in accordance with OECD TG 475
Determination of the dosage range and establishment of the main experimental design based on the physicochemical properties of the test substance
Definition of the negative control, the solvent control, and appropriate positive control groups; scientific justification of the route of administration, dosage levels, duration of administration, and sampling times; compliance with ethical approval and animal welfare requirements
OECD TG 475 assesses structural chromosome aberrations in rapidly dividing tissues such as bone marrow. It may not, on its own, reflect tissue-specific effects or effects occurring only in certain cell types. Sensitivity to numerical chromosome changes may be limited; additional tests, such as the micronucleus test, may be required to assess anogenetic potential. When interpreting the results, the pharmacokinetics of the test substance, its metabolic activation, species differences, and other genotoxicity tests conducted concurrently should be taken into account. The test should not be evaluated in isolation in regulatory decision-making processes but rather as part of a “weight-of-evidence” approach.
For information on test design, sample acceptance criteria, and reporting procedures for your studies in accordance with OECD TG 475, please contact Nano-Test.