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Home Ames Test Mouse Lymphoma Assay Chromosome Aberration Test Micronucleus Test Rat Liver UDS Test Comet Assay ICH and FDA recommendations Links |
Introduction to Comet Assay Comet assay, also known as single cell gel electrophoresis (SCG), is a microgel electrophoresis technique which detects DNA damage and repair in individual cells. The assay gets its name from the appearance of a genetically damaged cell. First, the cell is set in a gel and lysed. Second, an electric current is run across the cell. If the cell's DNA was damaged by double-strand breaks, single strand breaks and/or strand breaks induced by alkali-labile sites in the alkaline version of the assay, there will be some short broken strands. Because DNA is negatively charged, the electric current causes those small broken pieces to migrate through the gel faster and further than larger, unbroken pieces. As a result, a damaged cell takes on the appearance of a comet, with the broken bits of damaged DNA forming the tail. The pieces of DNA are smaller and smaller, the further they migrate from the cell body. Therefore, the longer the tail, smaller the pieces, and the greater the genetic damage. The length and fragment content of the tail is directly proportional to the amount of DNA damage.Comet assay is increasingly being used in genotoxic testing of industrial chemicals, agrochemicals and pharmaceuticals. It is favored in early drug development as a mechanistic and genotoxic predictor. Results are obtained in mere days, the test is easy to perform, requires small amounts of test article (no more than 50 mg) and can be performed in almost any eukaryotic cells (different animal organs). Although it is essentially a method for measuring DNA breaks, lesion-specific endonucleases now allow for the detection ultraviolet (UV)-induced pyrimidine dimers, oxidized bases, and alkylation damage. Outline:
In vivo Comet Assay This is a Tier II assay that provides further information in the event of a positive test result in the initial FDA / ICH GLP genetic toxicology tests. Most importantly, it provides this information at the organ tissue level such as lung, liver, stomach, bone marrow, bladder, kidney, skin and eyes.In vitro Comet Assay This is the version of the test most useful for drug screening in early developmental phases. A number of cell lines have proven useful for this test.Relative to other genotoxicity tests, the comet assay is inexpensive, rapid and simple 
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