In Vivo Test For Chromosomal Damage Using Mammalian Hematopoietic Cells
Micronuclei are cytoplasmic chromatin-containing bodies formed when acentric chromosome fragments or chromosomes lag during anaphase and fail to become incorporated into daughter cell nuclei during cell division. Because genetic damage that results in chromosome breaks, structurally abnormal chromosomes, or spindle abnormalities leads to micronucleus formation, the incidence of micronuclei serves as an index of these types of damage.
It has been established that essentially all agents that cause double strand chromosome breaks (clastogens) induce micronuclei. Because enumeration of micronuclei is much faster and less technically demanding than is scoring of chromosomal aberrations, and because micronuclei arise from two important types of genetic damage (clastogenesis and spindle disruption), the micronucleus assay has been widely used to screen for chemicals that cause these types of damage.
Mammalian erythrocyte micronucleus assay
This in vivo micronucleus test is used for the detection of damage induced by the test substance to the chromosomes or the mitotic apparatus of erythroblasts by analysis of erythrocytes as sampled in bone marrow and/or peripheral blood cells of animals, usually rodents.
The purpose of the micronucleus test is to identify substances that cause cytogenetic damage that results in the formation of micronuclei containing lagging chromosome fragments or whole chromosomes.
Visualization of micronuclei is facilitated in these cells using specific staining techniques and because they lack a main nucleus. An increase in the frequency of micronucleated polychromatic erythrocytes in treated animals is an indication of induced chromosome damage.
Limitations to the use of standard in vivo tests
There are compounds for which standard in vivo tests do not provide additional useful information. This includes compounds for which data from studies on toxicokinetics or pharmacokinetics indicate that they are not systemically absorbed and therefore are not available for the target tissues in standard in vivo genotoxicity tests. In cases where sufficient target tissue exposure cannot be achieved, it may be appropriate to base the evaluation only on in vitro testing.