[Distinguishing apoptotic cells from DNA strand-broken cells by comet assay]

Apoptosis of immature thymocyte of mice induced by dexamethasone and DNA strand-broken cells induced by K2Cr2O7 were tested by comet assay. The results showed that the morphology of apoptotic cells assayed by comet was special. Under the same condition, the time of apoptotic cells running on electrophoresis was shorter than DNA-broken cells. The length of comet tail of DNA strand-broken cells increased in a dose-response relation with the increase of K2Cr2O7, whereas, the apoptotic index increased with the dosage of dexamethasone. While DNA damage was repairing, apoptosis continued to process. The DNA strand-broken cells could be obviously seen while DNA damage was repairing. It was suggested that comet assay could be used to detect DNA strand break sensitively, but also could distinguish different grades of DNA damage, which is helpful for studies on the etiology, progressing and outcome of cancer.