Chromosomal Aberration Analysis

Structural chromosome aberrations are apparent breaks and/or rearrangements within or between chromosomes. These breaks and rearrangements are visible through a light microscope and are observed in metaphase chromosomes. They are a consequence of cellular exposure to a chromosome breaking agent (clastogen) resulting in a break followed by failure or error of repair mechanisms. These induced lesions in the chromosome persist for one or more cell cycles. The lesions are visible in a metaphase chromosome as strand breaks or rejoin inappropriately.

Most cells exposed to chemical clastogens must undergo a period of DNA synthesis to convert initial DNA lesions into chromosome alterations visible at mitosis. At defined intervals after exposure to the clastogen, the cells are treated with a metaphase-arresting substance, Colcemid ®, then harvested and stained. Metaphase cells are subsequently analyzed microscopically for the presence of chromosomal aberrations.

	"The structural chromosome aberration assay is part of the current battery of genetic toxicology tests recommended by global regulatory agencies." Pat Curry, PhD Senior Biologist

Many mutagens do not act directly on DNA but require conversion to reactive intermediates by enzymes found in the liver; that is, the original compound or promutagen must be metabolized to the ultimate mutagenic chemical structure. Cells in culture typically have little or no capacity to metabolize test articles (depending on the cell type). Induced rat hepatic microsomes with cofactors are included in culture medium during treatment to provide bioactivation, thereby enhancing the ability of the assay to detect clastogenic metabolites.

Numerical changes in the chromosomes are not determined by this protocol. However, the occurrence of polyploidy or endoreduplication, which will be recorded, may indicate that the test article has the potential to induce numerical aberrations.