Micronucleated cell

The micronucleus assay may be used not only for the detection of acute but also chronic genetic damage. In mice, chromosomal breakage in bone marrow erythroblasts produces an accumulation of micronuclei in normochromatic erythrocytes in peripheral blood and there is little, if any, selective removal of micronucleated cells from circulation. This is not the case with rats, which limits their usefulness in long-term studies using peripheral blood. 

Cytogenetic effects were not found in bone marrow cells from mice treated with 1,4-dichlorobenzene by gavage at levels up to 1,800 mg/kg/day in a 13-week study (NTP 1987). No increase in micronucleated cells occurred even at levels that were extremely toxic to the test animals, resulting in liver toxicity and decreased survival rates. As noted by the authors of that study, the observed carcinogenic activity of... 

No increase in % kinetochore-positive micronuclei compared with controls Supplemented with arachidonic acid increase in both kinetochore-positive and -negative micronucleated cells compared with controls (CREST-... 

Genotoxic, when at least one effluent concentration demonstrated that the median of micronucleated cells was significantly different from that of controls. 

Suspect, when the median of micronucleated cells was double that of control animals although not significantly different. 

Structural/numerical chromosome damage is evaluated by the increase in the number of micronucleated cells, scored out of 1000 cells in three analyzable concentrations. The compound is considered positive if either ... 

Konopacka, M., Rzeszowska-Wolny, J. (2006). The bystander effect-induced formation of micronucleated cells is inhibited by antioxidants, hut the parallel induction of apoptosis and loss of viability are not affected. Mutat. Res. 593 32-8. 

Microcell A cell fragment, containing one to a few chromosomes, formed by the enucleation or disruption of a micronucleated cell. 

Micronucleated cell A cell that has been mitotically arrested and in which small groups of chromosomes function as foci for the reassembly of the nuclear membrane, thus forming micronuclei, the maximum of which would be equal to the total number of chromosomes. 

To ensure that the results of an assay are valid, specific criteria have been determined. The frequency of micronucleated cells need to be within the normal historical control range. The frequency of micronucleated cells in the positive controls need to be significantly increased over the vehicle control. In addition, there must be five surviving animals per group. 

Ballarin C, Sarto F, Giacomelli L, et al. 1992. Micronucleated cells in nasal mucosa of formaldehyde-exposed workers. Mutat Res 280 1-7. 

In the micronucleus test, no mutagenic activity was observed in the bone marrow cells of mice fed diets containing 1330, 5330, or 10,670 ppm annatto daily for 7 days. An increased frequency of micronucleated cells was observed with coadministration of cyclophosphamide in animals fed the highest concentration of annatto, as compared to cyclophosphamide alone (Alves de Lima et al. 2003). 

Stich, H.F., Stich, W., and Parida, B.B., 1982b, Elevated frequency of micronucleated cells in the buccal mucosa of individuals at high risk for oral cancer betel quid chewers, Cancer Lett., in press. 

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