Oxidation of Cellular DNA Measured with the Comet Assay

The comet assay, or alkaline single-cell gel electrophoresis, originated as a simple and sensitive method for detecting DNA strand breaks in cells such as peripheral blood lymphocytes, cultured cells, and disaggregated tissue, e.g., liver (1 ,2 ). Cells embedded in a thin layer of agarose on a microscope slide are lysed with detergent and high salt, and the resulting nucleoids electrophoresed at high pH. DNA is drawn out of the nucleoid to form a “comet tail” (see Note 1 ). Comets are visualized by fluorescence microscopy, after staining with a suitable DNA-binding dye. The relative amount of DNA in the tail compared with the head reflects the number of DNA breaks present.