Cytogenetic test

Subcllnlcal effects clinical laboratory test alteration (liver function, nerve conduction velocity), mutagenicity testing, cytogenetic testing Requires estimation of eventual likelihood of clinical disease predicted by subcllnlcal abnormalities ... 

OECD (1983). OECD Guidelines for the Testing of Chemicals. No. 475. Genetic toxicology in vivo mammalian bone marrow cytogenetic test chromosomal analysis. Adopted 4 April 1984. 

Galloway, S.M., Bloom, A.D., Resnick, M., Margolin, B.H., Nakamura, F., Archer, R Zeiger, E. (1985) Development of a standard protocol for in vitro cytogenetic testing with Chinese hamster ovary cells Comparison of results for 22 compounds in two laboratories. Environ. Mutag, 1, 1-51... 

There are also differences in cellular sensitivity in the different stages of the cycle. In cytogenetic tests, cells in different stages of the cycle must be treated and analyzed. If the study is to be carried out in vivo on cycling cells or in vitro on asynchronous cells, a single treatment will expose cells in all stages of the cycle. 

Each cytogenetic test system has advantages and disadvantages. For instance, if a very simple determination of a compound s ability to produce chromosomal aberrations in vivo is desired, a bone marrow assay is probably simplest and least expensive. If, however, genetic hazards to future generations are of primary concern, assays of germ cells would be more appropriate. In in vitro assays of peripheral lymphocytes or cell lines, the cells can be made synchronous or fairly synchronous. 

A simpler, quicker, and less expensive cytogenetic test uses sister chromatid exchange (SCE). SCEs are detected in chromosomes that have been treated in such a way that the two sister chromatids of a chromosome differ chemically and thus stain differently. Most chemical mutagens induce SCEs at concentrations lower by a factor of about 100 than those needed to produce significant yields of ordinary chromosomal aberrations. The major exception to this is the small group of chemicals that, like x rays, produce double strand breaks in DNA and induce aberrations at all stages of the cell cycle. 

Like other cytogenetic tests, SCE tests can be performed on cells treated in culture or in vivo. For the in vivo method, cells from treated animals can be excised and cultured in vitro in the presence of BrdUrd or the animal itself can be given an injection or infusion of BrdUrd so that SCE can be observed in bone marrow or spermatogonial cells directly. The latter method is one of the simplest and least expensive ways to observe the effects of chemicals in gonads. The test is not limited to mammalian cells, but has been successfully carried out in plants, insects, and fish. 

Cytogenetic methods with plant root tips206—especially those of Vicia, Allium, and Hordeum—were widely used in the 1950s and 1960s to study the effects of chemicals on chromosomal structure and have played an important part in the development of cytogenetic tests in genetic toxicology. 

Many chromosomal alterations can be detected in plants,149 and, in addition to studies of mitotic cells, methods using microsporocytes (i.e., pollen mother cells) have permitted the study of meiotic cells.263 Although basic research in plant cytogenetics continues, cytogenetic tests in plants have been replaced to some extent in genetic toxicology by mammalian cell-culture tests and tests in whole mammals. 

The decrease in the use of plant cytogenetic tests does not mean that there are no instances where plant cyto-... 

This test is usually much more sensitive, but considerably more expensive and slower, than the dominant-lethal test,131 and it deals with a clearly defined type of mutation that is transmitted to and scored in viable offspring. Males are exposed to the test substance and mated to untreated females. Male progeny (usually derived only from post-sperroatogonial treatments) are tested for translocations by the fertility test or the cytogenetic test. In the fertility test, males are tested, usually with a sequential procedure, to determine fertility rates.137 Animals suspected of having a translocation (because of decreased fertility) are then subjected to cytologic examination. 

Fluothane was negative in two Tier I tests (and not subjected to the third), but was positive in the Drosophila test. If fluothane had also had a negative result in the mammalian cytogenetic test, it would be the only example in this series of a substance that was mutagenic according to the Tier II test but was not detected in Tier I. 

Fertility and early embryonic development rats Developmental rats, rabbits Prenatal and postnatal development rats Genetic toxicology Ames test, in vitro mammalian chromosome aberration assay, in vivo cytogenetic test, FIGPRT test with V79 cells... 

This in vitro cytogenetic test is a clastogenicity test system for the detection of chromosomal aberrations in cultured mammalian cells or primary cultures. Chromosomal aberrations may be either structural or numerical. However, because cytogenetic assays are usually designed to analyze cells at their first posttreatment mitosis and numerical aberrations require at least one cell division to be visualized, this type of aberration is generally not observed in a routine cytogenetic assay. The best estimate of aberration frequency is the first cell division after the start of treatment. Structural aberrations are of two types chromosome or chromatid aberrations. 

Chromosomal aberration tests in vitro (e.g. Cytogenetic test) and in vivo (e.g. Micronucleus test in rodents). 

A test for gene mutations in bacteria An in vitro cytogenetic test in mammalian cells or in vitro mouse lymphoma tk assay... 

Hexachlorophene was not shown to be mutagenic in Salmonella typhimurium in tests reviewed. Cytogenetic tests with cultured human lymphocytes were also negative. 

Thus, SCE tests have been largely discontinued by industry and are recommended by regulatory agencies on a limited basis. However, this assay continues to be used as a research tool and in some regulatory settings. For example, despite its poor concordance, the SCE assay continues to be used by the NTP, in part because SCE techniques are sufficiently similar to those used for in vitro chromosomal aberration assays so that the two tests can efficiently be used in parallel by cytogenetic testing laboratories. 

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