The single cell gel electrophoresis assay for induced DNA damage (comet assay): measurement of tail length and moment

Cultured hepatocytes have been treated with either DMSO or dimethylnitrosamine(NDMA) for either 1 or 2 h and the cells assessed for DNA-damageusing the single cell alkaline gel electrophoresis assay (cometassay). A strong positive test response was observed producingcomet tails of a length and DNA content not observed in eitherviable or dead control cells. A stronger test response was observedafter a 2 h, as opposed to a 1 h, incubation of hepatocyteswith NDMA. The method of processing the image of the comet isdiscussed and it is proposed that measurement of the lengthof the comet tail should commence at the estimated trailingedge of the cell, rather than at the leading edge or the estimatedcentre of the cell. Using this criterion, many control cellshave no comet tails thereby enabling chemically induced tailsto be more readily assessed. A simplified version of definingthe comet tail moment is proposed. ³To whom correspondence should be addressed